WO2007149501A2 - Process for preparing dendritic polymers using microwave assisted synthesis - Google Patents

Abstract

The present invention provides an improved process for preparing dendritic polymers where a core is reacted with a branch cell reagent (BR) and/or an extender using microwave radiation wherein, compared with prior processes, the amount of (BR) required is not in large excessive amounts, the time of the reaction is greatly reduced, and the purity of the final dendritic polymer is increased.

Description

PROCESS FOR PREPARING DENDRITIC POLYMERS USING MICROWAVE ASSISTED SYNTHESIS

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to the synthesis of dendritic polymers using microwave assisted synthesis.

Description of Related Art

Dendrimers are highly branched, often spherical molecules in which branches may terminate at charged amino groups that radiate from a central core molecule. Amine- terminated dendrimers have a high density of positively charged amine groups on the surface, such as with PAMAM dendrimers. Due to controlled chemical synthesis, dendrimers have a very precise size and defined shape.

Dendritic polymers have often been thought desirable to make various products because of their unique physical characteristics, such as biocompatibility when desired, interior void space for many such polymers, highly charged surface that is able to be surface modified, solubility features that can be adjusted for the purpose, to name a few.

Currently the processes available to prepare dendritic polymers tend to be time consuming and often require large excesses of one or more of the reactants and solvents. Both disadvantages result in high costs of the processes. In addition, thermal reactions used in these processes often lead to product mixtures and require difficult separations to obtain the desired purity of the product. Thus there is a need for a process that overcomes these issues.

BREEF SUMMARY OF THE INVENTION

The present process for preparing dendritic polymer structures of the present invention provide the advantages of faster preparation time to make the desired product, easier separations and fewer steps, resulting in greater purity of the final product. MWA processes have been found to lead to products with no or little impurities, at almost stoichiometric compositions of the reactants and can be carried out often in minutes rather than days. The present invention concerns a process for preparing a dendritic polymer which comprises reacting a core (C) with at least one branch cell reagent (BR) and/or an extender using MWA synthesis wherein, compared with prior processes, the amount of (BR) required is not in large excessive amounts, the time of the reaction is greatly reduced, and the purity of the final dendritic polymer is increased. Click chemistry can also be used.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the comparison of Sample 3 (right lane) and Sample 7 (left lane) from Table 1. The spot at Rf =0.56 is the desired product. The thermal reaction has many more by-products located at about Rf = 0.1 and the base line is very strong, suggesting a less clean reaction.

Figure 2 shows the TLC for Gl .0-epoxy made by the present process. Figure 3 shows the TLC of the reaction of tetra-azide using stoichiometric amount of NaN3. The left lane is the tetra-azide, and the right lane is the reaction mixture. Compared with the tetra-azide made by adding large excess of NaN₃ at 55⁰C method, the new spot is the desired product.

Figure 4 shows the infrared spectra of PAMAM dendrimer G=3.5 after 1^st (A) and 10^th (C) irradiation. Part (B) is the enlarged indicated portion of Part (A) and Part (D) is the enlarged indicated portion of Part (C).

Figure 5 shows PAGE of microwaved PAMAM G=4 product of Example 11 together with ladder of PAMAM dendrimers G=3 to G=6 with amine surface.

DETAILED DESCRIPTION OF THE INVENTION Glossary

The following terms as used in this application are to be defined as stated below and for these terms, the singular includes the plural.

BR or (BR) means a branch cell

C or (C) means a core of a dendrimer or dendron Celite means diatomaceous earth (Fisher Scientific)

DAB means diaminobutane

DCM means dichloromethane DEA means diethanolamine

DETA means diethylenetriamine

DI water means deionized water

Diglyme means diethylene glycol dimethyl ether DMF means dimethylformamide

DMSO means dimethylsulfoxide

EDA means ethylenediamine; Aldrich

EPI means epichlorohydrin, usually further distilled prior to use eqυiv. means equivalents) EPON 1031 means l,2,2-tetrakis(4-(oxiran-2-ylmethoxy)phenyl)ethane

EX or (EX) means an extender

FF or (FF) means a focal point functionality component of a core

G means dendrimer generation, which is indicated by the number of concentric branch cell shells surrounding the core (usually counted sequentially from the core) g means gram(s)

HPLC means high pressure/performance liquid chromatography

IF or (IF) means interior functionality

IR means infrared spectrometry

L means liter(s) MALDI-TOF means matrix-assisted laser desorption ionization time of flight mass spectroscopy

Me means methyl

MeOH means methanol mg means milligram(s) Mins. means minutes mL means milliliters)

MWA means microwave assisted

NMR means nuclear magnetic resonance

N-SIS means nanoscale sterically induced stoichiometry PAGE means poly(acrylamide) gel electrophoresis

PAMAM means poly(amidoamine), including linear and branched polymers or dendrimers with primary amine terminal groups

PEHAM means poly(etherhydroxylamine) dendrimer PEI means poly(ethyleneimine)

PETGE means pentaerythritol tetraglycidyl ether

Percent or % means by weight unless stated otherwise

Ph means phenyl PIPZ means piperazine

POPAM means a PPI core surrounded by PAMAM dendrons

PPI means poly(propyleneimine)

Rf means relative flow in TLC

RT means ambient temperature or room temperature, about 20-25⁰C SEC means size exclusion chromatography

SIS means sterically induced stoichiometry

TF means a terminal functionality

THF means tetrahydrofuran

TLC means thin layer chromatography TPETGE means tetraphenylolethane tetraglycidyl ether

TREN means -m(2-aminoethyl)amine

TRIS means frø(hydroxyrnethyl)aminomethane

UF means ultrafiltration

UV-vis means ultraviolet and visible spectroscopy W means Watt(s)

This invention describes an improved synthesis of dendritic polymers. Also this invention describes the improved purity, fewer steps and separations needed to obtain these dendritic polymers.

Chemical structures of Dendritic Polymers

The dendritic polymer structures of the present invention maybe any dendritic polymer, including without limitation, PAMAM dendrimers, PEHAM dendrimers, PEI dendrimers, POPAM dendrimers, PPI dendrimers, polyether dendrimers, dendrigrafts, random hyperbranched dendrimers, polylysine dendritic polymers, arborols, cascade polymers, avidimers or other dendritic architectures. There are numerous examples of such dendritic polymers in the literature, such as those described in Dendrimers and other Dendritic Polymers, eds. J.MJ. Frέchet, D. A. Tomalia, pub. John Wiley and Sons, (2001) and other such sources.

These dendritic polymers can be any physical shape, such as for example spheres, rods, tubes, or any other shape possible. The interior structure may have an internal cleavable bond (such as a disulfide) or an internal functionality such as a hydroxide or other group to associate with it. Additionally, the Dendritic polymer can be a dendron. This dendron can have any dendritic polymer constituents desired.

General Syntheses Used to Prepare Dendritic Polymers Most of these dendritic polymers have been taught in the literature. See Dendrimers and other Dendritic Polymers, eds. J.M.J. Frέchet, D. A. Tomalia, pub. John Wiley and

Sons, (2001) where most of these structures are discussed. The PEHAM dendritic polymers have been taught in WO2006/065266 and WO2006/115547.

However, all those dendritic polymer structures were prepared by methods other than that now taught and claimed by this invention.

Syntheses Used to Prepare Dendritic Polymers by the Process of the Present Invention

MWA synthesis has exhibited unexpected and dramatic advantages compared to thermal processing. It was observed that MWA produced higher purity dendritic polymer products (i.e., dendrimers/dendrons) under more mild conditions, shorter reaction times (minutes versus days), while requiring only stoichiometric amounts or slight excess of reacting reagents. The dendritic polymer as the starting material or a desired (C) is reacted with a BR or EX to obtain the desired dendritic polymer product. Suitable solvents can be used, including but not limited to methylene chloride, THF, toluene, methanol, diethyl ether, DMF, DMSO, water, and hexane, if the reactant does not also serve as the solvent. The mild conditions, at temperatures in the range of from about -35°C to 200⁰C, for the reaction compared to that of the prior thermal reaction leads to less by-products with fewer steps for purification of the desired dendritic polymer product. The reaction times are significantly reduced compared to the prior thermal process. For example, approximately an 18 fold reduction in reaction time was noted; wherein a thermal process requiring about 3 days or 72 hours was reduced to 4 hours while producing higher quality products by using these microwave techniques. Thus this MWA synthesis is less expensive to run to make the product desired. For the following examples the various equipment and methods were used to run the various described tests for the results reported in the examples described below.

Equipment and Methods Size Exclusion Chromatography (SEO

A methanolic solution of Sephadex™ (Pharmacia) purified dendrimer was evaporated and reconstituted with the mobile phase used in the SEC experiment (1 mg/mL concentration). All the samples were prepared fresh and used immediately for SEC.

Dendrimers were analyzed qualitatively by the SEC system (Waters 1515) operated in an isocratic mode with refractive index detector (Waters 2400 and Waters 717 Plus Auto Sampler). The analysis was performed at RT on two serially aligned TSK gel columns (Supelco), G3000PW and G2500PW, particle size 10 μm, 30 cm * 7.5 mm. The mobile phase of acetate buffer (0.5M) was pumped at a flow rate of lmL/min. The elution volume of dendrimer was observed to be 11-16 mL, according to the generation of dendrimer.

High Pressure/Performance Liquid Chromatography CHPLCI

High pressure liquid chromatography (HPLC) was carried out using a Perkin Elmer™ Series 200 apparatus equipped with refractive index and ultraviolet light detectors and a Waters Symmetry Ci₈ (5 μm) column (4.6 mm diameter, 150 mm length). A typical separation protocol was comprised of 0.1% aqueous acetic acid and acetonitrile (75:25% v/v) as the eluant and UV light at λ = 480 nm as the detector.

Thin Layer Chromatography (TLO

Thin Layer Chromatography was used to monitor the progress of chemical reactions. One drop of material, generally 0.05M to 0.4M solution in organic solvent, is added to a silica gel plate and placed into a solvent chamber and allowed to develop for generally 10- 15 mins. After the solvent has been eluted, the TLC plate is generally dried and then stained (as described below). Because the silica gel is a polar polymer support, less polar molecules will travel farther up the plate. "Rf" value is used to identify how far material has traveled on a TLC plate. Changing solvent conditions will subsequently change the R_f value. This Rf is measured by the ratio of the length the product traveled to the length the solvent traveled. Materials: TLC plates used were either (1) "Thin Layer Chromatography Plates - Whatman®" PK6F Silica Gel Glass backed, size 20 x 20 cm, layer thickness: 250 μm or (2) "Thin Layer Chromatography Plate Plastic sheets - EM Science" Alumina backed, Size 20 x 20 cm, layer thickness 200 μm. Staining conditions were: (1) Ninhydrin: A solution is made with 1.5 g of ninhydrin,

5 mL of acetic acid, and 500 mL of 95% ethanol. The plate is submerged in the ninhydrin solution, dried and heated with a heat gun until a color change occurs (pink or purple spots indicate the presence of amine). (2) Iodine Chamber: 2-3 g of I₂ is placed in a closed container. The TLC plate is placed in the chamber for 15 mins. and product spots will be stained brown. (3) KMhQ* Stain: A solution is prepared with 1.5 g OfKMnO₄, 10 g of K₂CO₃, 2.5 mL of 5% NaOH, and 150 mL of water. The TLC plate is submerged in KMhO₄ solution and product spots turn yellow. (4) UV examination: An ultraviolet (UV) lamp is used to illuminate spots of product. Short wave (254 nm) and long wave (365 run) are both used for product identification.

MALDI-TOF Mass Spectrometry

Mass spectra were obtained on a Bruker Autoflex™ LRF MALDI-TOF mass spectrometer with Pulsed Ion Extraction. Mass ranges below 20 kDa were acquired in the reflector mode using a 19 kV sample voltage and 20 kV reflector voltage. Polyethylene oxide was used for calibration. Higher mass ranges were acquired in the linear mode using a 20 kV sample voltage. The higher mass ranges were calibrated with bovine serum albumin.

Typically, samples were prepared by combining a 1 μL aliquot of a 5 mg/mL solution of the analyte with 10 μL of matrix solution. Unless otherwise noted, the matrix solution was 10 mg/mL of 2,5-dihydroxybenzoic acid in 3:7 acetonitrile:water. Aliquots (2 μL) of the sample/matrix solution were spotted on the target plate and allowed to air dry at RT.

Dialysis Separation In a typical dialysis experiment about 500 mg of product is dialyzed through a dialysis membrane with an appropriate pore size to retain the product and not the impurities. Dialyses are done in most examples in water (other appropriate dialyzates used were acetone and methanol) for about 21 hours with two changes of dialyzate. Water (or other dialyzate) is evaporated from the retentate on a rotary evaporator and the product dried under high vacuum or lyophilized to give a solid.

Ultrafiltration Separation OIF') A typical ultrafiltration separation protocol was as follows: A mixture of product and undesired compounds was dissolved in the appropriate volume of a solvent for this mixture (e.g., 125 mL of MeOH) and ultrafiltered on a tangential flow UF device containing 3K cutoff regenerated cellulose membranes at a pressure of 20 psi (137.9 kPa) at 25°C. The retentate volume as marked in the flask was maintained at 100-125 mL during the UF collection of 1500 mL permeate (~ 5 hours). The first liter of permeate was stripped of volatiles on a rotary evaporator, followed by high vacuum evacuation to give the purified product. Depending on the specific separation problem, the cut-off size of the membrane (e.g., 3K, 2K or IK) and the volume of permeate and retentate varied.

Sephadex™ Separation

The product is dissolved in the minimum amount of a solvent (water, PBS, or MeOH) and purified through Sephadex™ LH-20 (Pharmacia) in the solvent. After eluting the void volume of the column, fractions are collected in about 2-20 mL aliquots, depending on the respective separation concerned. TLC, using an appropriate solvent as described before, is used to identify fractions containing similar product mixtures. Similar fractions are combined and solvent evaporated to give solid product.

Nuclear Magnetic Resonance (NMR) - ¹H and ¹³C

Sample preparation: To 50-100 mg of a dry sample was add 800-900 μL of a deuterated solvent to dissolve. Typical reference standards are used, i.e., trimethylsilane. Typical solvents are CDCl₃, CD₃OD, D₂O, DMSO-de, and acetone-dβ. The dissolved sample was transferred to an NMR tube to a height of ~ 5.5 cm in the tube.

Equipment: (1) 300MHz NMR data were obtained on a 300MHz 2-channel Varian™ Mercury Plus NMR spectrometer system using an Automation Triple Resonance Broadband (ATB) probe, WX (where X is tunable from ¹⁵N to ³¹P). Data acquisition was obtained on a Sun Blade™ 150 computer with a Solaris™ 9 operating system. The software used was VTMMR vβ.lC. (2) 500MHz NMR data were obtained on a 500MHz 3-channel Varian™ Inova 500MHz NMR spectrometer system using a Switchable probe, H/X (X is tunable from ¹⁵N to ³¹P). Data acquisition was obtained on a Sun Blade™ 150 computer with a Solaris™ 9 operating system. The software used was VNMR v6.1C.

Atomic Force Microscopy (AFM) or Scanning Probe Microscopy (SPM) All images were obtained with a Pico-SPM™ LE AFM (Molecular Imaging, USA) in DI water with tapping mode, using Multi-purpose large scanner and MAC mode Tips [Type π MAClevers, thickness: 3 μm, length: 225 μm, width: 28 μm, resonance frequency: ca 45 KHz and force constant: ca 2.8 N/m (Molecular Imaging, USA)]. Typically, 3 lines/sec, scan speed was used for scanning different areas, with a set point of 0.90 of the cantilever oscillation amplitude in free status. To avoid hydrodynamic effect of thin air gaps, the resonance was carefully measured at a small tip - sample distance.

Polvacrylamide Gel Electrophoresis (PAGE)

Dendrimers that were stored in solvent are dried under vacuum and then dissolved or diluted with water to a concentration about 100 mg in 4 mL of water. The water solution is frozen using dry ice and the sample dried using a lyophilizer (freeze dryer) (LABCONCO Corp. Model number is Free Zone 4.5 Liter, Freeze Dry System 77510) at about -47°C and 60 x 10^"3 mBar. Freeze dried dendrimer (1-2 mg) is diluted with water to a concentration of 1 mg/mL. Tracking dye is added to each dendrimer sample at 10% v/v concentration and includes (1) methylene blue dye (1% w/v) for basic compounds (2) bromophenol blue dye (0.1% w/v) for acid compounds (3) bromophenol blue dye (0.1%w/v) with 0.1% (w/v) SDS for neutral compounds.

Pre-cast 4-20% gradient gels were purchased from ISC BioExpress. Gel sizes were 100 mm (W) X 80 mm (H) X 1 mm (Thickness) with ten pre-numbered sample wells formed in the cassette. The volume of the sample well is 50 μL. Gels not obtained commercially were prepared as 10% homogeneous gels using 30% acrylamide (3.33 mL), 4 X TBE buffer (2.5 mL), water (4.17 mL), 10% APS (100 μL), TEMED (3.5 μL). TBE buffer used for gel electrophoresis is prepared using lr/s(hydroxymethyl)aminomethane (43.2 g), boric acid (22.08 g), disodium EDTA (3.68 g) in 1 L of water to form a solution of pH 8.3. The buffer is diluted 1 :4 prior to use.

Electrophoresis is done using a PowerPac™ 300 165-5050 power supply and BIO- RAD™ Mini Protean 3 Electrophoresis Cells. Prepared dendrimer/dye mixtures (5 μL each) are loaded into separate sample wells and the electrophoresis experiment run. Dendrimers with amine surfaces are fixed with a glutaraldehyde solutions for about one hour and then stained with Coomassie Blue R-250 (Aldrich) for about one hour. Gels are then destained for about one hour using a glacial acetic acid solution. Images are recorded using an hp ScanJet™ 5470C scanner.

Infrared Spectrometry fIR or FTIRI

Infrared spectral data were obtained on aNicolet Fourier™ Transform Infrared

Spectrometer, Model G Series Omnic, System 20 DXB. Samples were run neat using potassium bromide salt plates (Aldrich).

Ultraviolet/Visible Spectrometry (UV/Vis)

UV-VIS spectral data were obtained on a Perkin Elmer™ Lambda 2 UV/VIS

Spectrophotometer using a light wavelength with high absorption by the respective sample. for example 480 or 320 nm.

Microwave CMWA")

Microwave assisted synthesis was done using a multimode design Milestone ETHOS StartSYTH Labstation with a microwave cavity of 35 x 35 x 35 H cm. The labstation is equipped with dual magnetron system using a pyramid diffuser for a homogeneous microwave distribution in the cavity. The installed power is 1600 Watts

(2 magnetons 800 Watts) with a power delivery of 1000 Watts in 10 Watt increments. The unit contains a built — in ASM — 100 magnetic stirrer. Reactions were run in 12 mL or 50 mL glass tubes fitted with 15 bar pressure relief valves. Larger reactions were run in 100 mL and 250 mL capacity Teflon vessels also fitted with 20 bar pressure relief valves.

The invention will be further clarified by a consideration of the following examples, which are intended to be purely exemplary of the present invention.

Example 1: Research MWA click chemistry

A. General procedure and TLC results.

Propargyl triglycidyl ether ( 2 ) (60 mg, 0.165 mmol) was put in a 10 mL vial equipped with a magnetic stir bar. The tri-azide compound (1) (21 mg, 0.05 mmol) was then added to the vial. Solvent was added, followed by the addition of catalyst.

In the case OfCuSO₄ and sodium ascorbate, the catalysts were dissolved in water first and then added to the reaction vial.

The reaction mixtures were stirred well and the reaction vial was put in a 900W domestic microwave and heated for a certain amount of time stated in Table 1 below. Reaction results were checked by TLC immediately after the heating. The TLC ratings are from 0 to 10 (10 is the best result on TLC, but is not meant to mean 100% yield).

Table 1. The TLC rating for different solvents and catalysts using MWA click chemistry

* indicates that this sample was run under thermal conditions ** reaction efficiencies; wherein, 10 is the best rating

From Table 1, it appears that the water/f-butanol with CuSO₄/sodium ascorbate (Sample 3) and DMF with [Cu(MeCN)₄]PFe (Sample 5) are the two best conditions under which to run the title click reactions. Since Sample 3 is less expensive to use, the following studies choose this system as the standard reaction conditions.

Figure 1 shows the comparison of Samples 3 (right lane) and 7 (left lane). The spot at Rf =0.56 is the desired product. The thermal reaction has many more by-products located at about Rf = 0.1 and the base line is very strong, suggesting a less clean reaction. The following scheme illustrates this reaction.

Scheme 1

Example 2: Commercial MWA click chemistry

A. General procedure.

Milestone Ethos E microwave is used for all the following reactions and conditions are listed at each example. Generally, the two reaction components are mixed in the selected solvent and then the catalysts are added. The reaction mixture was stirred well for about 5 mins. The reaction tube was put in the microwave and heated for a certain amount of time as shown. The solvent was removed and the products were purified.

B. Synthesis of G 1.0-epoxy

In a 2.0 cm (O.D.) x 12 cm microwave tube was put 1 (416 mg, 0.964 mmol), then 2 was transferred to the tube in f-butanol. The total volume of f-butanol used was 3.0 mL. The mixture was mixed well. A solution of sodium ascorbate (60.3 mg, 0.304 mmol, in 1.5 mL of DI) was added, followed by the addition of a solution OfCuSO₄-SH₂O (38 mg, 0.152 mmol in 1.5 mL of DI). The reaction was stirred vigorously for 5 mins. Then the reaction tube was placed into the microwave with parameters listed in Table 2 below. Table 2

Solvent was then removed using a rotary-evaporator and the residue was put on high vacuum for 10 min. The residue was then taken up in 20 mL of DCM, washed with water (1x30 mL). The water layer was then extracted with DCM (2x20 mL). The combined organic layer was washed with brine (1x30 mL) and dried with Na₂SO.). The solvent was removed to give the crude product. The product was purified with a silica gel column using acetone:toluene (2:1) as eluent. The product 3 was obtained as a clear oil. (735 mg, 67% yield).

TLC: R_f =0.52 CH₂Cl₂/MeOH (100:7). (See Figure 2.)

MALDI-TOF: Calculated for C₆₆Hi₀₇N₉O₂₇, 1458.60; found, 1461.42(M+H). ¹H NMR (CDCl₃, 300MHz): δ ppm 0.83(t, 3H), 1.36(q, 2H), 2.55(m, 6H), 2.75(m,

6H), 3.08 (m,6H), 3.1 l-3.46(m, 51H), 3.67(m, 6H)₃ 3.74(m, br, 6H), 4.15(m, br, 6H), 4.18(m, br, 6H), 4.56(m, 6H), 7.74(s, 3H).

¹³C NMR: 7.82, 23.13, 43.64, 44.40, 45.79, 51.19, 53.38, 55.21, 69.16, 69.35, 70.13, 71.96, 72.24, 72.72124.15, 145.62 ppm.

Figure 2 shows the TLC for this product 3. The two spots indicate the presence of G = 1.0 (epoxy), structure 3 which were obtained from two fractions isolated from the silica gel column.

The following scheme illustrates this reaction.

03

Scheme 2

C. Synthesis of G2.0-epoxy

In a 2.0 cm (O.D.)x 12 cm microwave tube was put 4 (184.6 mg, 0.10 mmol). Then 2 was transferred to the tube in f-butanol. The total volume of /-butanol used was 1.20 mL. The mixture was mixed well. A solution of sodium ascorbate (42 mg, 0.20 mmol, in 0.25 mL of DI) was added, followed by the addition of a solution of CuSO₄ SH₂O (26 mg, 0.10 mmol in 0.25 mL of DI). The reaction was stirred vigorously for 5 mins. Then the reaction tube was placed into the microwave with parameters listed in Table 3 below.

Table 3

The solvent was then removed using rotary-evaporator and the residue was put on high vacuum for 2 hours with a periodic argon blow. The product was purified with a silica gel column using DCM (10:1) as eluent. The product 5 was obtained as a clear oil (155.4 mg, 55% yield).

TLC: R_f =0.43 CH₂CI₂/MeOH (8:1).

IVIALDI-TOF: Calculated for C₂I₉H₃₅₀N₃₆O₉₀₅4927.31; found, 4926.55(M+H).

¹HMMR (CDCl₃, 300MHz): δ ppm 0.83(t, 3H), 1.35(q, 2H), 2.56(m, 9H), 2.75(m, 9H), 3.08 (m,9H), 3.11-3.46(m, 126H), 3.67(m, 9H), 4.13(s, br, 9H), 4.24(s, br, 6H), 4.36(m, 18H), 4.55(m, 36H), 7.76(s, 9H), 7.82(s, 3H). ¹³CNMR: 7.85, 44.39, 45.74, 45.80, 46.05, 51.18, 53.20, 64.72, 65.17, 69.24, 70.12, 70.23, 72.24, 72.81, 124.32, 124.92, 144.56, 145.42ppm.

The following scheme illustrates this reaction.

Scheme 3

D. Synthesis of G0.5-Tetra-azide

Tetraglycidyl ether (360 mg, 1.0 mmol) (Scheme 4) was put in a microwave tube. Then 0.5mL of DMF was added and mixed well using a magnetic stir bar. A solution of sodium azide (273 mg in 0.75 mL of water, 4.2 mmol, 1.05 equiv./epoxy) was added, followed by the addition of a solution of ammonium chloride (263 mg in 0.75 mL of water). A sticky material precipitated around the stir bar. DMF was added (4x0.5 mL) to make the mixture clear. The mixture was stirred at RT for 3 min. and then put in the microwave with the following parameters as shown in Table 4 below. Table 4

A mini-workup was done. 0.25 mL of reaction mixture was dried and 0.5 mL of DCM and 0.5 mL of water were added to the residue and shaken well. The organic layer was checked by TLC. The result showed that the reaction was completed and clean.

Figure 3 shows the left lane is the tetra-azide, and the right lane is the reaction mixture. Compared with the tetraazide made by adding a large excess of NaN3 at 55 ⁰C, the new spot is the desired product.

The following scheme illustrates this reaction.

Scheme 4

Example 3: Preparation of PEHAM dendrimer, G = 1.0, epoxy surface from pentaerythritol tetra-azide and propargyl triglycidyl ether using MWA Synthesis.

Propargyl triglycidyl ether, 2 (0.684 g, 2.0 mmol) was placed into a 15-mL screw cap vial. A solution of pentaerythritol tetra-azide, 1 (0.266 g, 0.5 mmol) in 2.0 g of t- butanol was added, followed by addition of 2.0 g of water. Sodium ascorbate (0.04 g, 0.2 mmol) (Acros Organics) was added to this reaction mixture, followed by CUSO45H2O powder (0.025 g, 0.1 mmol) (Acros Organics). The vial was closed halfway, mixed well, placed in a microwave oven (Samsung™, Model MW830WA), and heated for 21 seconds at 100OW. The reaction mixture started to boil and turned brick-red in color. The reaction progress was monitored by TLC (2: 1 acetone:toluene; iodine vapor used to visualize the spots). TLC indicated complete reaction and the new spot at R_f= 0.44 was identified as Gl .0 dendrimer. The reaction mixture was transferred into a separatory funnel and diluted first with 30 mL of water, followed by 30 mL of DCM and 30 mL of brine solution. After thorough mixing, the organic layer was separated and the aqueous layer extracted with DCM (2x30 mL). The combined organic layers were dried over Na2SC>4, concentrated on a rotary evaporator to give a pale yellow colored liquid, which was further dried under high vacuum to give the desired G 1.0 dendrimer, 3 (1.145 g). Proton NMR indicated some amount of t- butanol left with the product.

¹H NMR (300 MHz, CDCl₃): δ 2.53-2.57 (12H, m), 2.71-2.75 (12H, m), 3.05-3.10 (12H, m), 3.26-3.32 (H, m), 3.36-3.53 (H, m), 3.66 (H, dd, J=2.70 Hz'), 4.12 (H, m), 4.38 (H, m), 4.57 (H, m), 7.73 (4H, s); and

¹³CNMR (75 MHz, CDCl₃): δ 44.37, 44.40, 45.77, 45.87, 45.92, 46.01, 51.06, 51.15, 53.06, 65.19, 69.16, 70.11, 72.22, 72.66, 73.98, 74.30, 124.21, 145.50; and

IR(Neat): 3357, 3135, 3055, 2999, 2919, 2876, 1647, 1480, 1332, 1252, 1165, 1091,906,844,785 cm^"1.

The following scheme illustrates this reaction.

Scheme 5 Example 4: Preparation of PEHAM dendrimer, G = 1.5, azide surface from PEHAM dendrimer, G = I, epoxy surface using MWA Synthesis.

PEHAM dendrimer G1.0, 3 (0.951 g, 0,5 mmol) (made from Example 3) was placed in a 50-mL microwave glass reaction vessel and 12 mL of DMF and 6.0 mL of water were added. The vessel was equipped with a stir bar, and sodium azide, NaN₃ (0.429 g, 6.6 mmol) (Aldrich) and ammonium chloride, NH₄CI (0.35 g, 6.6 mmol) (EM Science) were added successively. The reaction vessel was closed and irradiated (7 min at 8O⁰C and 500W) using a Milestone Microwave Laboratory systems, ETHOS™ E Series. TLC (2: 1 acetone:toluene) revealed that only a small amount of G1.0 epoxy dendrimer, 3 was still present after this treatment. The reaction mixture was transferred into a 100-mL round bottom flask and heated at 6O⁰C for overnight. The reaction mixture was allowed to cool to RT, and then 30 mL of water and 300 mL of MeOH were added. Insoluble solids were filtered off through a Celite plug. The filtrate was subjected to UF through a IKDa size exclusion membrane in order to remove excess NaN₃ and NH4CI and the side product NaCl. After collecting of 800 mL of permeate, the retentate was withdrawn from the UF and concentrated by rotary evaporation at low temperature (<45°C) to give a olive green colored viscous liquid, which was further dried under high vacuum to give the desired G 1.5 dendrimer, 4 (1.46 g). IR showed a strong stretching vibration at 2098 cm^'1 for the presence of azides, while vibrations for the starting epoxy functionality was absent.

¹H NMR (300 MHz, CD₃OD): δ 3.23-3.36 (H, m), 3.40-3.60 (H, m), 3.80-3.87 (H, m), 4.11-4.16 (H, m), 4.45 (H, m), 4.57 (s, m); and

¹³C NMR (75 MHz, CD₃OD): δ 45.08, 45.56, 45.68, 53.32, 53.83, 58.27, 64.15, 68.13, 68.81, 69.01, 69.51, 69.76, 70.02, 70.47, 72.75, 74.57, 125.16, 144.72; and IR (Neat): 3333, 2919, 2876, 2098, 2036, 1665, 1486, 1449, 1387, 1363, 1276, 1097,924,863,671 cm^"1.

The following scheme illustrates this reaction.

Scheme 6

Example 5: Preparation of PEHAM dendrimer, G = 2.0, epoxy surface from PEHAM dendrimer, G = 1.5, azide surface using MWA Synthesis.

A 50-mL microwave glass reaction vessel was charged with PEHAM dendrimer, G1.5, azide surface, 4 (1.2 g, 0.5 mmol) and 4.0 g of /-butanol and 4.0 g of water. Propargyl triglycidyl ether, 2 (2.052 g, 6.0 mmol) was added to this solution. The reaction vessel was equipped with a stir bar, and sodium ascorbate (0.119 g, 0.6 mmol) (Acros Organics) and C11SO₄.5H₂O (0.075 g, 0.3 mmol) were added. The reaction vessel was closed, placed in a microwave oven (Milestone Microwave Laboratory systems, ETHOS™ E Series), and irradiated for 3min at 70⁰C and 500W. TLC (2:1 acetonertoluene; iodine vapor used to visualize the spots) indicated a new spot with 0.11 for PEHAM dendrimer G2.0, epoxy surface, 5. The absence of the azide vibration in the IR spectrum confirmed complete reaction of all azides. This epoxide was kept as starting material for future reactions without further characterization to protect the reactive epoxy groups.

The following scheme illustrates this reaction.

Scheme 7

Example 6: Preparation of PEHAM dendrimer, G = I, alcohol surface from EPON 1031 and diethanolamine using MWA Synthesis.

A. General Procedure

To a 100-mL glass reaction tube fitted with a pressure relief valve (15 bar, 221 psi) and a stir bar was added EPON 1031 (4 g, 6.43 mmol assuming 100% TPETGE) as a solution in 12 g of ethyleneglycol dimethyl ether. To this mixture was added DEA (3.3 g, 31.4 mmol, 1.2 equiv. based on 100% purity EPON 1031, 1.6 equiv. per epoxide with ~ 60% purity) and 4 g of MeOH . The reaction tube was sealed and fitted with a temperature probe. A end of a Tygon™ tube was attached to a copper coil immersed in isopropanol — dry ice at ~ -78°C with N₂ gently blowing through was placed next to the reaction vessel for cooling. The power of the microwave instrument was set at 500W with the QP set at ~

50%. The irradiation sequence was set at 4 mins. from RT to 100⁰C then 20 mins. at 100°C. Typical irradiation pulses were 22 seconds and summed to a total of 8 mins. per 24 min. interval for a total of 4 intervals to give 10 min. irradiation time. A total irradiation time was 40 mins. This mixture was cooled to RT and the volatiles were removed by a rotary evaporator followed by high vacuum to give 7.4 g of crude material. The reaction was monitored by TLC using 30% NH₄OH in MeOH.

B. Purification by Sephadex™ LH -20

A 2.8 g aliquot of this crude material from Part A was dissolved in 7 g of MeOH and purified on a Sephadex™ LH-20 column in MeOH (void volume: 365 mL) taking

40 fractions of 8 mL each and developing fractions by TLC (10% NH₄OH in MeOH). Fractions 1 - 19 were collected that contained material with a baseline R_f only and found to be free of DEA by TLC. The volatiles of these fractions were stripped on a rotary evaporator followed by high vacuum to give 477 mg. Fractions 20 - 30 contained some baseline R_f material along with material ranging in Rf from 0.1 to 0.7. These fractions were collected and stripped to give 805 mg. Fractions 31 -40 were found to contain only product of Rf ~ 0.8 - 0.9. This material was stripped of volatiles to give 530 mg. Fraction 41 was collected as a volume of 250 mL and was found to contain DEA with some UV active material and was stripped to give 1.1 g. The total weight of product obtained from fractions 1 - 40 was 1.81 g (79% yield based on 100% purity of EPON 1031).

¹H NMR (300MHz, CD₃OD) δ 2.4 - 2.9 ( bm, 6H), 3.4 - 3.7 ( bm, 4H), 3.7 - 4.2 ( bm, 5H), 6.2 - 7.5 ( bm, 9H).

¹³C NMR (75 MHz, CD₃OD) δ 21.70, 57.45, 58.24, 59.61, 68.02, 70.10, 114.17, 129.46, 137.39, 156.96, 158.65. C. Purification by UF

A 2.5 g aliquot of this crude mixture from Part A was dissolved in 150 mL of MeOH and ultrafiltered on a tangential flow UF device containing IK regenerated cellulose membranes at 22 - 25 psi with temperature of the solution maintained at 35 -38^°C. The retentate volume in the flask was kept from 75 — 100 mL during the process while 1 L of permeate was obtained. The retentate was removed and the unit was washed with 3x130 mL of MeOH. The retentate and washes were collected and stripped on a rotary evaporator followed by high vacuum to give 1.51 g (66 % yield based on 100% purity of EPON 1031). The permeate was stripped of volatiles to give 1.9 g of material that contained mostly DEA and some UV active material as determined by TLC (10% NH4OH in MeOH).

¹H NMR (300MHz, CD₃OD) δ 2.4 - 2.8 ( bm, 6H). 3.4 - 3.7 ( bm, 4H), 3.7 - 4.2 ( bm, 5H)₅ 6.4 - 7.5 (bm, 9H).

¹³C NMR (75 MHz₅ CD₃OD) δ 21.29, 57.44, 58.24, 59.618, 68.03, 70.07, 114.02, 129.35, 137.07, 156.91.

D. Purification by Precipitation

A final 2.5 g aliquot of the crude mixture from Part A was dissolved in 6 g of MeOH and added dropwise to 200 mL of mechanically stirred DI. This heterogeneous mixture was allowed to settle for one hour and the yellow homogeneous aqueous layer was filtered through a Whatman No 1. The yellow solid clinging to the walls of the flask was dissolved in MeOH. Some solid that was retained on the filter paper was dissolved in MeOH and combined with the bulk material. The volatiles were removed from the mixture using a rotary evaporator and the yellow solid was evacuated at high vacuum overnight at 25°C to give 1.27 g ( 56% yield based on 100% pure EPON 1031).

¹U NMR (300MHz, CD₃OD) δ 2.4 - 2.8 (bm, 6H), 3.4 - 3.7 (bm, 4H), 3.7 - 4.2 (bm, 5 H), 6.4 - 7.5 (bm, 9H).

¹³C NMR (75 MHz, CD₃OD) δ 21.32, 57.43, 58.23, 59.64, 68.04, 70.05, 70.26, 113.99, 129.35, 137.07, 156.91. The following scheme illustrates this reaction.

C54H82N4O16 Exact Mass: 1042.57

MoI. Wt.: 1043.25 C, 62.17; H, 7.92; N, 5.37; O₁ 24.54

Scheme 8 Example 7: Preparation of PEHAM Dendrimer, G= 1 , Sodium Carboxylate Surface from PETGE and Iminodiacetic Acid Using MWA Synthesis

To a 50-mL reaction tube fitted with a pressure relief valve, a thermowell for a thermocouple, and a stir bar was added iminodiacetic acid (1.3 g, 9.S mmol, 19.5 mmol acid), sodium hydroxide (781 mg, 19.5 mmol) and 4 g of DI. This mixture was stirred to give a homogeneous solution. To this mixture was added PETGE (760 mg, 2 mmol, 8 mmol epoxide) in 2 g of MeOH. This mixture was sealed and irradiated with 500W microwave power for 40 mins. at 100^°C. A TLC of the reaction mixture showed no starting material remaining. This mixture was purified by tangential flow ultrafiltration at 22 psi in DI with 1 K regenerated cellulose membranes with retentate at 3 -5% solids and giving a permeate of 6 recirculations. Evacuation of volatiles using a rotary evaporator followed by high vacuum at 25°C for 18 hours gave 1.89 g ( 89% yield).

¹³C NMR (75 MHz, D₂O) δ 45.47, 57.76, 58.72, 66.91, 70.15, 73.60, 178.50, MALDl-TOF: Calculated for C₃₃H₄₈N₄O₂₄, 1458.60; found, 1461.42(M+H).

The following scheme illustrates this reaction.

a 100° C, 40 min. a Microwave, 500 W water, MeOH

Ci7^H28°8

Exact Mass: 360.18

P

Scheme 9

Example 8: Preparation of Epiiodohydrin from EPI using Sodium Iodide: MWA Synthesis and Workup in Diethyl ether

To a 100-mL Teflon™ reactor vessel containing a stir bar was added sodium iodide (10.8 g, 65 mmol, 1.1 equiv. per EPI), 52 g of acetonitrile (ACROS) and EPI (5.44 g, 58.8 mmol) (ACROS). This mixture was made homogeneous with stirring. The vessel was sealed and placed in a MicroSYN™ microwave reactor irradiating at 500W with temperature set at 80⁰C with stirring. The reaction mixture was irradiated for 45 — 50 mins. at 80°C. Examination of an aliquot of this mixture by ¹³C NMR spectroscopy indicated the complete disappearance of EPI signals and the appearance of the product signals only. This mixture was cooled to 25°C and acetonitrile was removed using a rotary evaporator. This liquid - solid mixture was extracted with diethyl ether 8 x 20 mL until the ether was colorless. The ether layers were collected and stripped of volatiles on a rotary evaporator followed by high vacuum at RT to a constant weight to give 6 g ( 55% yield) of the title compound.

¹H NMR (300MHz, CD₃CN ) δ 2.61 - 2.65 ( m , IH), 2.90 - 2.95 (m , IH), 3.18 - 3.25 ( m, 2H).

¹³C NMR (75 MHz, CD₃CN ) δ 6.53, 50.65, 52.50.

The following scheme illustrates this reaction.

Finkelstein Reaction 1.1 NaI , ^cl _^-<? ¹N^?

CH₃CN

C₃H₅IO

Microwave Exact Mass: 183.94

Epichlorohydrin MoI. WL: 183.98

80⁰C₁ 500 Watts C, 19.59; H. 2.74; I₁ 68.98; O, 8.70

Epiiodohydrin

Scheme 10

Example 9: Preparation of Epiiodohydrin from EPI using Sodium Iodide: MWA Synthesis and Workup in Methylene Chloride

To a 270-mL Teflon™ reactor vessel containing a stir bar was added sodium iodide (43.4 g, 65 mmol, 1.1 equiv. per EPI), 160 g of acetonitrile (ACROS) and EPI (21.7 g, 58.8 mmol) (ACROS). This mixture was made homogeneous with stirring. The vessel was sealed and placed in a MicroSYN™ microwave reactor irradiating at 500W with temperature set at 80⁰C with stirring. The reaction mixture was irradiated for 76 mins. at 80^°C. Examination of an aliquot of this mixture by ¹³C NMR spectroscopy indicated about 5 — 10% of EPI remaining of EPI signals and the appearance of the product signals. This mixture was cooled to 25°C and acetonitrile was removed using a rotary evaporator. This liquid — solid mixture was dissolved with DCM (100 mL). The organic layer was washed with 30 mL of water. The organic layer was drained from the separatory funnel to 90 mL. This layer was dried with anhydrous sodium sulfate, filtered and stripped of volatiles to give 25 g of material. This mixture was evacuated with high vacuum at 25°C to a constant weight of 20 g (47% yield ).

Above Scheme 10 shows this product.

Example 10: Preparation of Epiiodohydrin from EPI using Sodium Iodide: MWA Synthesis and Workup in Diethyl ether

To a 100 mL Teflon™ reactor vessel containing a stir bar was added sodium iodide (11 g, 66 mmol, 1.0 equiv. per EPI), 52 g of acetonitrile (ACROS) and EPI (6.0 g, 64.8 mmol) (ACROS). This mixture was made homogeneous with stirring. The vessel was sealed and placed in a MicroSYN™ microwave reactor irradiating at 500W with temperature set at 80⁰C with stirring. The reaction mixture was irradiated for 75 mins. at 8O⁰C. Examination of an aliquot of this mixture by ¹³C NMR spectroscopy after 47 mins. of irradiation indicated EPI signals in about 40% of the mixture and the appearance of the product signals. After a total of 75 mins. of irradiation a ' H NMR spectrum indicated the mixture contained 22% of EPI and 78% epiiodohydrin. This mixture was cooled to 25°C and acetonitrile was removed using a rotary evaporator. This liquid — solid mixture was extracted with diethyl ether 5 x 40 mL until the ether was colorless. The ether layers were decanted, collected and stripped of volatiles on a rotary evaporator followed by high vacuum at RT to give a constant weight of crude product (8.0 g). Correction for the amount of residual acetonitrile and ether by ¹H NMR spectroscopy indicated a 7.5 g (80% yield) of the desired compound. The weight of inorganic salts was 5.3 g.

Above Scheme 10 shows this product as epiiodohydrin.

Example 11: Preparation of PEHAM dendrimer, G = I, amine surface from EPON 1031 and Bis(methylisobutyliminoethyl)amine using MWA Synthesis

A. Reaction 1

To a 12-mL glass reaction tube fitted with a pressure relief valve (15 bar, 221 psi) and a stir bar was added EPON 1031 (500 mg, 8.04x10-4 mol theory, ~ 70% TPETGE) as a solution in 2.5 g of diglyme. A 2.5 g solution of bis(methylisobutyliminoethyl)amine in methyl isobutyl ketone, 400 mg/1.0 g solution, was weighed and evacuated of volatiles on a vacuum pump to give 1.0 g, 3.74 mmol, 1.2 equiv. per epoxide assuming 100% purity and 1.67 equiv. assuming ~ 70% purity. This amine was dissolved in 2.5 g of MeOH and added to the reaction mixture. The reaction tube was sealed and fitted with a temperature probe. A end of a Tygon™ tube attached to a copper coil immersed in isopropanol - dry ice at ~78°C with N₂ gently blowing through was placed next to the reaction vessel for cooling. The program was set for a ramp up from RT reaction temperature to 4O⁰C for 2 mins. followed by 18 mins. where irradiation occurs until 40⁰C then shuts off until the reaction cooled to this temperature. Typical pulse times were 22 seconds. Thus the irradiation time was computed from a 10 min. irradiation sequence by adding all the pulses together and found to be 7 — 8 mins. The entire procedure took 7 hours. The mixture was transferred to a SO mL round bottom flask with a MeOH rinse and 1 g of DI was added and the mixture stirred and heated at 6O⁰C under N₂ for 18 hours with flask fitted to a reflux condenser. This mixture was stripped of volatiles on a rotary evaporator followed by high vacuum gives 1.2 g of crude material. This material was dissolved in 5 g of MeOH and purified on a Sephadex™ LH-20 column with a void volume of 365 mL in MeOH. A total of 40 fractions were taken of 8 mL each. Product was collected in fractions 1 -20 as determined by TLC (10% NH₄OH in MeOH). These fractions were stripped of volatiles to give 493 mg. Fractions 21-30 were collected and stripped to give 150 mg. ¹H NMR (300 MHz, CD₃OD) δ 2.2 - 2.9 (bm, 12H), 3.6 - 4.2 ( bm, 6H), 6.3 - 7.5

(bm, 9H).

¹³C NMR (75 MHz, CD₃OD) δ 21.72, 38.91, 57.22, 57.69, 68.04, 70.21, 113.96,129.39, 137.14, 156.96.

B. Reaction 2

To a 12-mL glass reaction tube fitted with a pressure relief valve (15 bar, 221 psi) and a stir bar was added EPON 1031 (1.0 g, 1.61 mmol theory, ~ 70% TPETGE) as a solution in 3.0 g of diglyme. A 5 g solution of bis(methylisobutyliminoethyl)amine in methyl isobutyl ketone, 400 mg/l.Og solution, was weighed and evacuated of volatiles on a vacuum pump to give 2.0 g, 3.74 mmol, 1.2 equiv. per epoxide assuming 100% purity and 1.67 equiv. assuming ~ 70% purity. This amine was dissolved in 2.5 g of MeOH and added to the reaction mixture. The reaction tube was sealed and fitted with a temperature probe. A end of a Tygon™ tube attached to a copper coil immersed in isopropanol — dry ice at ~78°C with N₂ gently blowing through was placed next to the reaction vessel for cooling. The irradiation sequence was set at 2 mins. From RT to 100⁰C then 8 mins. at 100°C. Typical irradiation pulses were 22 seconds and summed to a total of 2.5 mins. per 10 min. interval for a total of 4 intervals to give 10 min. irradiation time. A total irradiation time was 40 mins. This mixture was heated at 60⁰C with 10 mL of DI for 18 hours under N₂. The volatiles were removed by rotary evaporator followed by high vacuum to give 2.2 g of crude material. This crude material was dissolved in 6 g of MeOH and purified on a Sephadex™ LH-20 column in MeOH (void volume: 365 mL) taking 40 fractions of 8 mL each and developing fractions by TLC (10% NH4OH in MeOH). Fractions 1 — 35 were collected and found to be free of DETA produced by the hydrolysis of bis(methylisobutyliminoethyl)amine by TLC. The volatiles of these fractions were stripped on a rotary evaporator followed by high vacuum to give 1.3 g. ¹H NMR (300MHz, CD₃OD) δ 2.53 (bs, 6H)₅ 2.64 (bs, 6H), 3.6 - 4.2 (bm, 6H)₅ 6.4

-7.6 (bm, 9H).

¹³C NMR (75 MHz, CD₃OD) δ 38.93, 57.23, 57.70, 68.07, 70.20, 113.97, 129.39, 137.15, 156.96.

The following scheme illustrates this reaction.

Sephadex LH - 20

Scheme 11

Example 12: Preparation of PAMAM Tecto - Dendrimer, G = 5 (G= 2.5 Methyl ester)x from PAMAM dendrimer, DAB Core, G = 5, Amine Surface, Excess PAMAM dendrimer, DAB Core, G = 2.5 methyl ester; MWA Synthesis

To a 12-mL round bottom flask containing a stir bar and fitted with a N2 bubbler was added PAMAM dendrimer, diaminobutane core, G = 2.5 methyl ester surface (1.8 g, 2.97 mmol, 31 equivs. per G = 5 ) and 2.8 g of MeOH. To this homogeneous solution was added lithium chloride (450 mg , 10.6 mmol, ~ 1 equiv. per methyl ester). This mixture was made homogeneous with stirring. To this mixture cooled to 4°C was added PAMAM dendrimer, diaminobutane core, G = 5, amine surface (287 mg, 9.9 x 10^"6 mol) dissolved in 2.0 g of MeOH dropwise over about 2-3 mins. This resulting mixture was warmed to 40^&C and closed with a pressure relief cap containing an immersion well that dipped into the solution. A thermocouple was inserted in the immersion well of the reaction vessel. This mixture was setup in a Milestone ETHOS™ MicroSYNTH™ lab station with the power set at 500W. This reaction mixture was irradiated with microwaves for 2.9 hours at 50^°C. Analysis by SEC indicated all the G = 5 starting material disappeared to form higher molecular weight material that corresponded to a G = 6 — 7 PAMAM dendrimer. This material was irradiated for 26 mins. at 65°C with no further reaction observable by SEC. This size exclusion chromatogram was essentially identical to the same reaction that was stirred and heated at 40⁰C for 25 days in a sealed vessel. This mixture was added dropwise over 3 hours to rapidly stirred TREN (60 g, 411 mmol, 43 equivs. per ester) and 15 g of MeOH cooled at 4^°C. This resulting mixture was stirred at RT for 4 days sealed under a blanket OfN₂. An infrared spectrum of this material indicated the complete disappearance of the ester absorption at 1736 cm^'1. The total weight of the mixture at 92 g was diluted to 2L with Dl and ultrafiltered on a 30 K membrane to give 2L permeate. This mixture was concentrated to IL and ultrafiltered to give 2L permeate (IL concentrate + IL permeate). This mixture was concentrated to 500 mL and ultafiltered to give IL of permeate. This mixture was concentrated to 250 mL and ultrafiltered to give 1.2 L of permeate. The retentate was collected and stripped of volatiles on a rotary evaporator. The resulting residue was dissolved in MeOH. This mixture was stripped of volatiles on a rotary evaporator 3 times. This residue was evacuated at high vacuum at 25°C overnight to give 635 mg.

Example 13: Preparation of PAMAM Dendrimer, Diaminobutane Core, G = 2, Amine Surface, from PAMAM Dendrimer, G = 1.5 methyl ester and 100 Equivalents EDA per ester Using MWA Synthesis

To a 12-mL glass reaction tube fitted with a pressure relief valve (15 bar, 221 psi) and a stir bar was added EDA (5.2 g, 84.9 mmol, 100 equiv. per ester). To this stirred mixture cooled to ~ 6⁰C was added dropwise over ~ 5 mins. PAMAM dendrimer, DAB core, G = 1.5 methyl ester (150 mg, 5.3x10-5 mol, 8.5XlO^"4 mol ester) in 1.3 g of neat MeOH. This mixture was setup in a Milestone ETHOS™ MicroSYNTH™ lab station with the power set at 400W. This reaction mixture was irradiated with microwaves for 24 mins. (irradiation time: ~ 6 mins. at 40^°C). Analysis of the mixture after the first 3 mins. of irradiation at 40⁰C by IR indicated that 80 - 90% of the ester peak at ~ 1735 cm^'1 had disappeared. Further irradiation at 400W then 600W at 40⁰C for 12 mins. each (~ 3 mins. irradiation) showed no significant decrease in the ester peak in the IR spectrum. Further irradiation at 60°C at 600W , 800W and 900W for 12 mins. each ( ~ 4 - 5 mins. irradiation) showed small but noticeable decreases in the ester peak. Finally, irradiation at 900W for 1 hour at 60°C showed a significant decrease in ester carbonyl absorption. Irradiation at IOOOW at 6O⁰C for 1 hour caused the complete disappearance of the ester. This mixture was cooled to RT and stripped of volatiles on a rotary evaporator to give 171 mg of a viscous residue containing trapped EDA. This mixture as a 50% solution in MeOH was placed on a Sephadex™ LH — 20 column in MeOH and eluted with 30 X 4 mL fractions. Product was observed in fractions 2 - 24 as determined by TLC (10% NH4OH - MeOH) and were collected to give 80 mg product.

MALDI-TOF MS: C₁44H292N58 O₂s; CaIc. 3284, found 3278 (perfect structure), 3222 (perfect structure + 1 loop), 3165(perfect structure + 2 loops), 3108 (perfect structure + 3 loops), 3051 (perfect structure + 4 loops), 2993 (perfect structure + 5 loops) amu.

Example 14: Synthesis of PAMAM dendrimer G=4 from G=3.5 and TREN A. 1.1 Equiv. TREN per Ester TREN (653 mg, 146.2 mmol) was put in a microwave glass reaction tube equipped with a magnetic stir bar and cooled to 4°C using an ice-water bath. A solution of PAMAM dendrimer G=3.5, EDA core, ester surface (788 mg, 0.0634 mmol) in 0.5 mL of MeOH was added dropwise to the tube. The dendrimer container was rinsed with MeOH (2 x 0.5 mL) and the solvent added to the microwave tube. The reaction mixture was irradiated in the microwave for a series of times as shown in the Table 5 below. The IR spectrum of the mixture was recorded after each irradiation to monitor the reaction progress. The last irradiation cycle resulted in polymerization of the reaction mixture. 14403

Table 5

B. 10 Equivs. TREN per Ester

TREN (7.54 g, 51.53 mmol) was put in a microwave tube equipped with a magnetic stir bar and cooled to 4°C using an ice-water bath. A solution of PAMAM dendrimer G=3.5, EDA core, ester surface PAMAM dendrimer (1.0 g, 0.105 mmol) in 2.0 mL of MeOH was added dropwise to the tube. The dendrimer container was rinsed with MeOH (2 x 1.0 mL) and the solvent added to the microwave tube. The reaction mixture was irradiated in the microwave for a series of times as shown in Table 6 below. The IR spectrum of the mixture was recorded after each irradiation to monitor the reaction progress. After the reaction was completed as shown by the absence of the ester vibration at 1731 cm^*1 in the IR spectra (Figure 4), 350 mL of MeOH was added and the solution was purified by UF using a 1-KDa regenerated cellulose membrane. Permeate (1750 mL) was collected. Removal of solvent by rotary evaporation gave the product as a foam solid (1.53 g, 96.3% yield).

014403

Table 6

C. PAGE

PAGE of the purified product from Part B showed the formation of PAMAM dendrimer G=4 with some dimer and higher oligomers as by-products (Figure 5). For comparison, the ladder formed by STARBURST™ PAMAM dendrimers G=3 to G=6 with amine surface is also shown in Figure 5. The MALDI-TOF mass spectrum of the product gave the main peak at a mass of 17,030 amu..

The following scheme illustrates this reaction.

PAMAM;G4.θf EDA

Scheme 12 Although the invention has been described with reference to its preferred embodiments, those of ordinary skill in the art may, upon reading and understanding this disclosure, appreciate changes and modifications which may be made which do not depart from the scope and spirit of the invention as described above or claimed hereafter.

Claims

WHAT IS CLAIMED IS:

1. A process for preparing a dendritic polymer which comprises reacting a core (C) with at least one branch cell reagent (BR) and/or an extender (EX) using microwave radiation.

2. The process of claim 1 wherein the amount of (BR) required is stoichiometric or slightly in excess amounts.

3. The process of claim 1 wherein the time of the reaction is greatly reduced compared to prior thermal reactions.

4. The process of claim 1 wherein the reaction can be carried out at lower temperatures compared to prior thermal reactions.

5. The process of claim 1 wherein the purity of the final dendritic polymer is enhanced.

6. The process of any of claims 1-5 wherein the dendritic polymer is a PEHAM dendrimer.

7. The process of any of claims 1-5 wherein the dendritic polymer is a PAMAM dendrimer.

8. The process of any of claims 1 -5 wherein the dendritic polymer is a polylysine dendrimer.

9. The process of any of claims 1-5 wherein the dendritic polymer is a PPI dendrimer or a PEI dendrimer .

10. The process of any of claims 1-5 wherein the dendritic polymer is POPAM dendrimer, or polyether dendrimer.

11. The process of any of claims 1 -5 wherein the dendritic polymer is a dendrigraft, random hyperbranched polymer, arborol polymer, cascade polymer, or avidimer polymer.

12. The process of claim 1 where a suitable solvent is present.

13. The process of claim 1 wherein the BR or EX serves as the solvent.

14. The process of claim 1, 12 or 13 where in the core (C), extender (EX) or the branch cell (BR) contains epoxy, azide or acetylene groups such that these groups can react using click chemistry, in a solvent with a catalyst, then microwaved.