dendrimers and other dendritic polymers (frechet/dendrimers) || laboratory synthesis of...

25

Laboratory Synthesis ofPoly(amidoamine) (PAMAM)DendrimersR. ESFAND AND D. A. TOMALIAUniversity of Michigan, Center for Biologic Nanotechnology, Ann Arbor, MI,USA

1 INTRODUCTION

The divergent growth strategy, now widely used for dendrimer synthesis, wasdiscovered independently in parallel events that occurred in the Vogtle (Univer-sity of Bonn) and the Tomalia laboratories (the Dow Chemical Company) in1978—79. A brief communication from the Vogtle group [1] described thedivergent synthesis of several low molecular weight (i.e. � 1.5 kD) dendriticstructures derived from iterative reactions using acrylonitrile monomer. Asdescribed by the authors [2] and others [3], this critical chemistry was plaguedwith low yields, product isolation and analytical difficulties. More recently, thisprocess was modified to furnish a commercial route to poly(propyleneimine)(PPI) dendrimers (see Chapter 26).An analogous divergent methodology based on acrylate monomers was dis-

covered in 1979 and developed in the Dow Chemical Laboratories during theperiod of 1979—84. It was first reported at the 1st International (JSPS) Confer-ence, Japan Society of Polymer Science in Kyoto (1984) and published in 1985[4]. This approach provided high yields of poly(amidaomine) (PAMAM) den-drimers with molecular weights ranging from several hundred to over 1 millionDaltons (i.e. Generations 1—12) and is presently the preferred commercial routeto Starburst“ PAMAM dendrimers. Several significant advantages offered bythe divergent method include:

1. Allows direct dendritic growth of dendrons from a wide variety of atomic,

Dendrimers and Other Dendritic Polymers. Edited by Jean M. J. Frechet and Donald A. Tomalia© 2001 John Wiley & Sons Ltd

Dendrimers and other Dendritic PolymersEdited by Jean M. J. Frechet and Donald A. Tomalia

Copyright © 2001 John Wiley & Sons LtdISBNs: 0-471-63850-1 (Hardback); 0-470-84582-1 (Electronic)

molecular, polymeric as well as physical objects as cores. Does not require asecond core anchoring step which is sterically limited via the convergentmethod.

2. Adaptable to large volume scale-up (e.g. dendri-PAMAM and dendri-PPI areproduced in multi-kilogram quantities).

3. Low-cost, readily available commoditymonomers (i.e. acrylates, acrylonitrile,alkyleneamines) may be used for synthesis.

4. May be used to prepared high generation (i.e. G� 0—12) dendrimers thatprecede and exceed the ‘de Gennes dense packed’ state.

The procedures described are based on improved modifications from originalpublications [4—8]. They focus on the divergent ‘excess reagent’ syntheses ofdendri-poly(amidoamines) using various alkylenediamine cores. Examples ofboth divergent in situ branch cell methods, as well as divergent ‘preformed’branch cell methods are presented.Many of these dendrimeric nanostructures have shown commercial promise

as gene transfection, drug delivery agents, immunodiagnostics reagents, nano-catalysts, magnetic resonance imaging contrast agents, nanoreactors and nano-calibrators. Dendrimers are expected to play a significant role in the systematicdevelopment of nanoscale chemistry architecture and properties both in biologi-cal, as well as abiotic areas of interest.

2 GENERAL COMMENTS

Laboratory procedures are presented for two divergent methodologies, namely:(1) the in situ branch cell (BC) method, and (2) the preformed (BC) couplingmethod (Scheme 1). The divergent, in situ (BC) method is a two-step iterativeprocess for constructing poly(amidoamine) (PAMAM) dendrimers possessingeither terminal ester or amine groups. A shorthand designation for these struc-tures is as follows: [core]; (Generation)-dendri-PAMAM- (—CO

�Me/ —NH

�)�.

This method involves (a) alkylation with methylacrylate, and (b) amidation withethylenediamine (Scheme l). The alkylation step produces ester terminated (sub-shells) that are referred to as ‘half generations’ and are designated (Gn. 5). Thesecond step involves amidation of the ester terminated (Gn. 5) intermediates withlarge excesses of ethylenediamine to produce amine terminated, full generations,referred to as (Gn). These iteration sequences together with reaction conditionsare catalogued in Figure 25.1. The structures obtained from the first two reactionsequences are ‘starbranched’ PAMAMs. They are designated: [EDA](G:-.5)star-PAMAM—(CO

�Me)

�and [EDA](G:0)star-PAMAM—(NH

�)�, respectively.

The next iteration produces dendritic structures that are designated;[EDA](G:.5)dendri-PAMAM —(CO

�Me)

�and [EDA](G:l)dendri-PAMAM

—(NH�)�, respectively.

588 R. ESFAND AND D. A. TOMALIA

(i) In Situ Branch Cell Method

(ii) Preformed Branch Cell Method

N

NH2

CO2Me

N

CO2Me

CO2Me

CO2Me

CO2Me

N

CNH

CNH

N

CO2Me

CO2Me

Half Generations = Gn.5

Full Generations = Gn

NH2-(CH2)2-NH2

(excess) N

NH2

NH2

NH2

NH2

O

O

(b) Amidation Chemistry

(a) Alkylation Chemistry (Amplification)

N

CO2Me

CO2Me

N

CNH

CNH

O

O

(DMSO)

OH

OHH2NOH

OHOH

OH

OH

K2CO3

Scheme 1

The number of surface groups (Z), branch cells (BC) and molecular weights fora dendrimer series can be calculated with the math expressions shown below.These parameters, as well as hydrodynamic dimensions for the series[EDA](G:0-10)dendri-PAMAM—(NH

�)�are presented in Figure 25.1. The ex-

perimental procedures are general for a wide range of alkylenediamine initiatorcores (e.g., NH

�—(CH

�)—

�NH

�). Characterization data for dendri-PAMAMs de-

rived from these cores are included, where: n � 2, 3, 4, 5, 6.The preformed (BC) method is a one-step process used in this case to introduce

high multiplicity of terminal hydroxy groups. The method involves direct coup-ling of branch cell reagents (i.e. tris(hydroxymethyl)aminomethane (Tris-)) byamidation of ester terminated PAMAM dendrimers. Advancement to the nextgeneration of branch cells occurs in one step.

LABORATORY SYNTHESIS OF POLY(AMIDOAMINE) (PAMAM) DENDRIMERS 589

GenerationGenerationSurface GroupsSurface Groups

(Z)(Z)Molecular Molecular FormulaFormula MWMW Diameter (nm)Diameter (nm)

MW

=

NcNb

G-1

Nb-1

Nb-1

NbG-1

MRU + MtNbGMc + Nc

=

=

BC

Z NcNbG

Number ofBranch Cells

MolecularWeights

:

:

:

Number of CovalentBonds Formed/Generation=

Number ofSurfaceGroups

0 4 C22H48N10O4 517 1.41 8 C62H128N26O12 1,430 1.92 16 C142H288N58O28 3,256 2.63 32 C302H608N122O60 6,909 3.64 64 C622H1248N250O124 14,215 4.45 128 C1262H2528N506O252 28,826 5.76 256 C2542H5088N1018O508 58,048 7.27 512 C5102H10208N2042O1020 116,493 8.88 1,024 C10222H20448N4090O2044 233,383 9.89 2,048 C20462H40928N8186O4092 467,162 11.4

10 4,096 C40942H81888N16378O8188 934,720 ~13.0

G = 4G = 3

G = 2

G = 1

G = 5

ZZZ

ZZ

ZZ

ZZ

ZZ

ZZ

ZZZZZ

ZZZZZZZZZZZZ

CoreG = 0

Surface Group Amplification/Gen.

Dendrimer Core-Shell Mathematics

NbNc

=

Figure 25.1 (a) Dendrimer propagation mathematics; where: Nc, Nb = core,branch cell multiplicities; respectively, and G=generation; (b) mathematicallydefined values for surface groups (Z), molecular formulae and molecularweights (MW) as a function of generation for the (ethylenediamine core),poly(amidoamine) (PAMAM) dendrimer family.

3 EXPERIMENTAL METHODS

All reagents were purchased from Aldrich, Fluka, Sigma or Lancaster Synthesis,and were used after purification, unless otherwise stated. Solvents for reactions,work-up and purification procedures were used as supplied, unless otherwisestated. Solvent purification procedures were generally adopted from the book byPerrin and Armarego. Solutions were dried using anhydrous sodium sulfate ormagnesium sulfate, unless otherwise stated. Combustion analyses were meas-ured on a Perkin Elmer 240B or 240C elemental analyzer. Infrared spectra wererecorded on a Perkin-Elmer 983 InfraRed spectrophotometer. Mass spectrawere recorded by a VG Autospec mass spectrometer with ionization in a matrixof 3-nitrobenzyl alcohol. NMR spectra were recorded in deuterochloroform,unless otherwise stated, with a JEOL GX270 nuclear magnetic resonance spec-trometer (270.5 MHz). GPC was carried out on a Plgel mixed E column, withtetrahydrofuran (THF) as eluent, connected to a Knaur refractive index detectorand a PyeUnicam PU 410 computing integrator. The column was calibratedusing narrow dispersity linear polystyrene standards.


Generational Shells (Gn) and Sub-shells (G.5n)Reagents/ReactionConditions

Gen.dendri-Polyamidoamines

G=3.5

G=3.0

G=2.5

G=2.0

G=1.5

G=1.0

G=0.5

G=0

G=-0.5

Core

PAMAM-(NH2)32

PAMAM-(CO2Me)32

PAMAM-(NH2)16

PAMAM-(CO2Me)16

PAMAM-(NH2)8

PAMAM-(CO2Me)8

PAMAM-(NH2)4

PAMAM-(CO2Me)4

PAMAM-(CO2Me)64MeAcrylate, MeOH(2.4 eq./-NH2); 40…C/24 hrs

MeAcrylate, MeOH(2.4 eq./-NH2); 40…C/24 hrs




EDA, MeOH; 5…C/8 days(808 moles/ester)




(a)

(b)

(a)

(b)

(a)

(b)

(a)

(b)

(-CO2Me)(-CO2Me)(-CO2Me)

(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)

(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)

(-CO2Me)(-CO2Me)

(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)

(-CO2Me)(-CO2Me)

(-CO2Me)

(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)(-CO2Me)

(-CO2Me)(-CO2Me)(-CO2Me)

(-NH2) (-NH2) (-NH2)(-NH2) (-NH2)

(-NH2)(-NH2)

(-NH2)

(-NH2)(-NH2)

(-NH2)(-NH2)(-NH2)

(-NH2)(-NH2)

4

H2N (CH2)n-NH2Where: n = 2

Structures: [1] [2] [3] [4] [5] [6] [7]

0

1

2

3

Generations:

Figure25.2 Core–shell reaction sequence steps: (a) alkylation and (b) amidationsteps for preparation of G.5n and Gn. [NH2–(CH2)2–6–NH2]; (G =0–2.5)-dendri-poly(amidoamines)

3.1 DIVERGENT SYNTHESIS OF PAMAM DENDRIMERS VIAEXCESS REAGENT METHOD PREPARATION OF ESTERTERMINATED PAMAM STAR-BRANCHED PRECURSOR;[NH2-(CH2)2–6-NH2]; (G = -0.5); STAR-PAMAM(CO2ME)4; [1]

A solution of freshly distilled 1,2-diaminoethane (5 g, 5.5 ml, 0.083 mol) inmethanol (20 ml) was added dropwise to a stirred solution of methylacrylate(35 g, 37 ml, 0.407 mol) in methanol (20 ml), under nitrogen, over a period of 2 h.The final mixture was stirred for 30 min at 0°C and then allowed to warm toroom temperature and stirred for a further 24 h. The solvent was removed underreduced pressure at 40°C using a rotary evaporator and the resulting colourlessoil dried under vacuum (10�� mm Hg, 50°C) overnight to give the final product(32 g, 95%).

(�CH��CH

�)[N(�CH

��CH

��CO

��CH

�)�]�

Spectral characterization: IR v��/cm��: 1740 (C——O); �H NMR (CDCl

�) �

�: 3.61

(12H, s, e), 2.63 (8H, t, b), 2.41 (4H, s, a), 2.29 (8H, t, c); ��C NMR (CDCl�) �

�:

174.12 (d), 52.15 (e), 50.27 (b), 45.23 (a), 31.56 (c); Mass spectrum (FAB): m/z 405(MH), 427 (MNa); Elemental analysis: C

��H

��N

�O

�Calcd (%) C, 53.5; H,


Dendrimer [core] %Yield MW FAB-Ms (MH) GPC M/M

�

H2N—C�H

�—NH

�99 404 405 1.08

H2N—C�H

—NH

�95 418 419 1.01

H2N—C�H

�—NH

�96 432 433 1.03

H2N—C�H

��—NH

�91 445 447 1.01

H2N—CH

��—NH

�98 460 471 1.01

Analytical data for star-PAMAM(CO�Me)

�.

8.0; N, 6.9. Found (%) C, 53.2; H, 8.4; N, 7.1. Gel chromatography:M� 816.2,

M�

� 800.2, PD� 1.08.

3.2 PREPARATION OF AMINE TERMINATED PAMAMSTAR-BRANCHED PRECURSOR; [NH2–(CH2)2–6–NH2];(G =0); star-PAMAM(NH2)4; [2]

A solution of (G� 0.5); star-PAMAM](CO�Me)

�; [1] precursor (10 g, 0.025

mol) in methanol (20 ml) was carefully added to a vigorously stirred solution of1,2-diaminoethane (75 g, 85 ml, 1.248 mol) in methanol (100 ml) at 0°C. The rateof addition was such that the temperature did not rise above 40°C. Aftercomplete addition the mixture was stirred for 96 h at room temperature at whichtime no ester groups was detectable by NMR spectroscopy. The solvent wasremoved under reduced pressure maintaining the temperature no higher than40°C. The excess 1,2-diaminoethanewas removed using an azeotropicmixture oftoluene and methanol (9: 1). The remaining toluene was removed by azeotropicdistillation using methanol. Finally, removal of the remaining methanol undervacuum (10�� mm Hg, 40°C, 48 h) gave the tetra-amine terminated G� 0precursor as a colorless oil (12.5 g, 98%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

��NH

�)�]�

Spectral characterization: IR v��/cm��: 1640 (C——O), 3200 (NH

�), 3400 (NH);

�HNMR (CDCl�) �

�: 8.05 (4H, bt, e), 3.31 (8H, bq, f), 2.71 (8H, t, b), 2.57 (8H, t,.c),

2.53 (4H, s, a), 2.45 (8H, t, h), 2.25 (8H, p, g); ��C NMR (CDCl�) �

�: 175.15 (d),

51.31 (b), 48.25 (a), 45.32 (f), 35.18 (c), 31.25 (g); Mass spectrum (FAB): m/z 518(MH), 540 (MNa); Elemental analysis: C

��H

��N

��O

�Calcd (%) C, 51.1;

H, 9.3; N, 27.1. Found (%) C, 52.5; H, 9.7; N, 28.2.


Dendrimer [core] %Yield MW FAB-Ms (MH)

H2N—C�H

�—NH

�98 516 517

H2N—C�H

—NH

�95 530 531

H2N—C�H

�—NH

�94 544 545

H2N—C�H

��—NH

�92 558 559

H2N—CH

��—NH

�92 572 573

Analytical data for star-PAMAM(NH�)�.

Note: It is essential to carefully examine the analytical data for the presence ofcyclic compounds as a result of side reactions involved. The cyclization occurs asdendrimer amidation versus bridging amidation are kinetically similar. To pre-vent the intradendrimeric cyclization a large excess (50-fold) of 1,2-ethylenediamine is required. The excesses are removed to an undetectable levelby azeotropic techniques.

Ideal and Non-ideal Amidation of the dendri-PAMAM(CO2Me)4

Ideal growth Non-ideal growth

O

N

OMe

N

O

OMe

MeO

O

MeO

O

N (EDA)

NH2H2N

O

NH

N

O

OCH3

N(

(

N

HH:

O

NH

O

NH

NH

O

NH

N

O

NH2

NH2

H2N

H2N

N

O

N

NH

N

O

NH

N(

(

(EDA)

NH2H2N

[2]

[1]

Scheme 2


Synthesis of PAMAM Dendrimers

[3]

[1]

O

N

OMe

N

O

OMe

MeO

O

MeO

O

N

O

NH

O

NH

NH

O

NH

N

O

NH2

NH2

H2N

H2N

N

MeOHH2N

NH2

OMe

O

[1]

[2]

N OCH3

O

OOCH3

NH

N

O

O

NH

N

OCH3

OCH3

O

O

NH3CO

O

OH3CO

NH

N

O

O

NH

N

H3CO

H3CO

O

O

Scheme 2 (cont.)


[4]

[5]

N NH

NH2

O

O

NH2

NH

NH

N

O

O

NH

N

NH

NHNH2

O

O

NH2

NNH

H2N

O

O

H2N

NH

NH

N

O

O

NH

N

NH

NHH2N

O

O

H2N

NOCH3

O

OOCH3

N NHN

N

OCH3

OCH3

O

O

O

O

NH

NH

N

O

O

NH

N

NH

NH

OCH3

O

O

O

O

OCH3

N

NOCH3

O

O

NOCH3

NH3CO

O

OH3CO NNH

N

N

H3CO

H3CO

O

O

O

O

NH

NH

N

O

O

NH

N

NH

NH

H3CO

O

O

O

O

H3CO

N

NH3CO

O

O

NOCH3

Scheme 2 (cont.)


Dendrimer [core] %Yield MW FAB-Ms (MH) SECM/M

�

H2N—C�H

�—NH

�97 1205 1206 1.00

H2N—C�H

—NH

�92 1219 1220 1.01

H2N—C�H

�—NH

�93 1233 1234 1.05

H2N—C�H

��—NH

�96 1247 1248 1.05

H2N—CH

��—NH

�92 1261 1262 1.05

Analytical data for dendri-PAMAM(CO�Me)

�.

3.3 PREPARATION OF ESTER TERMINATED PAMAMDENDRIMER; [NH2-(CH2)2–6-NH2]; (G= 0.5);dendri-PAMAM(CO2Me)8; [3]

A solution of (G� 0); dendri-PAMAM(NH�)��; [2] precursor (8 g, 0.015mol) in

methanol (20 ml) was added to a stirred solution of methylacrylate (12.9 g, 13.5ml, 0.15 mol) in methanol (20 ml), under nitrogen, over a period of 1 h. The finalmixture was stirred at 0°C for 1 h and then allowed to warm to room tempera-ture and was stirred for a further 24 h. The solvent was removed under reducedpressure at 40°C and the resultant colorless oil vacuum dried (10�� mm Hg,50°C) overnight to give the final product (17.5 g, 92%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

�N(�CH

� CH

��CO

��CH

�)�)�]�

Spectral characterization: IR v��/cm��: 1750 (C——O), 3400 (NH); �H NMR

(CDCl�) �

�: 7.21 (4H, t, e), 3.65 (24H, s, k), 3.25 (8H, q, f), 2.65—2.95 (20H, m,.a, b,

g), 2.55 (16H, t, h), 2.45 (16H, t, i), 2.31 (8H, t, c); ); ��C NMR (CDCl�) �

�: 173.45

(d), 172.23 (j), 53.22 (k), 53.21 (f), 52.22 (b), 51.24 (g); Mass spectrum (FAB): m/z1207 (MH), 1229 (MNa); Elemental analysis: C

��H

�N

��O

��Calcd (%) C,

53.8; H, 8.1; N, 11.6. Found (%) C, 53.5; H, 8.2; N, 11.5. Gel chromatography:M

� 2465.1, M�

� 2471.3, PD� 1.0.

3.4 PREPARATION OF AMINE TERMINATED PAMAMDENDRIMER; [NH2-(CH2)2–6–NH2]; (G= 1.0);dendri-PAMAM (NH2)8; [4]

To a vigorously stirred solution of 1,2-diaminoethane (60 g, 65 ml, 0.994 mol) inmethanol (100 ml), at 0°C under nitrogen, was added a solution of (G� 0.5);dendri-PAMAM(CO

�Me)

�; [3] (5 g, 0.004 mol) in methanol (20 ml). The addi-

tion was controlled such that the temperature did not rise above 40°C. Themixture was stirred at room temperature for 96h, after which time no estergroups were detectable by NMR spectroscopy. The methanol was removed byvacuum distillation at � 40°C, and excess 1,2-diaminoethane was removed byazeotropic distillation using a mixture of toluene and methanol (9: 1). Theremaining toluene was removed by azeotropic distillation with methanol and



H2N—C�H

�—NH

�96 1429 1430

H2N—C�H

—NH

�92 1443 1444

H2N—C�H

�—NH

�92 1457 1458

H2N—C�H

��—NH

�93 1471 1472

H2N—CH

��—NH

�93 1485 1486

Analytical data for dendri-PAMAM(NH�)�.

finally the methanol removed under vacuum (10�� mm Hg, 50°C, 48 h) to givethe amine terminated G� 1.0 dendrimer as a pale yellow oil (5.7 g, 96%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

�N

(�CH� CH

��CO�NH�CH

��CH

��NH

�)�)�]�

Spectral characterization: IR v��/cm��: 1640 (C——O), 3420 (NH) ; �H NMR

(DMSO) ��: 8.03 (12H, bt, e, k), 3.31—3.15 (24H, bq, f, l), 2.65 (8H, t, g), 2.61—2.51

(52H, m,.a, b, c, h, i), 2.45 (16H, t, n), 2.25 (16H, bp, m); ��C NMR (DMSO) ��:

178.21 (d), 174.48 (j), 52.13 (f), 49.15 (l), 46.21 (g), 45.11 (a), 43.18 (b), 42.11 (c), 38.21(h), 35.51 (i); Mass spectrum (FAB): m/z 1430 (MH), 1452 (MNa); Elemen-tal analysis: C

�H

��N

�O

��Calcd (%) C, 52.1; H, 8.9; N, 25.5. Found (%) C,

49.3; H, 10.2; N, 24.2.

3.5 PREPARATION OF ESTER TERMINATED PAMAMDENDRIMER;[NH2-(CH2)2–6-NH2]; (G =1.5); dendri-PAMAM(CO2ME)16; [5]

A solution of (G� 1); dendri-PAMAM(NH�)�; [4] (6.5 g, 0.005 mol) in methanol

(20ml) was added to a stirred solution of methylacrylate (6.7 g, 7ml, 0.077mol) inmethanol (20 ml), under nitrogen, over a period of 2 h. The final mixture wasstirred at 0°C for 1 h and then allowed to warm to room temperature and stirredfor a further 24 h. The solvent was removed under reduced pressure at 40°C andthe resultant pale yellow oil vacuum dried (10��mmHg, 50°C) overnight to givethe final product (11.5 g, 91%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

�N(�CH

� CH

��CO�NH�CH

��C

H�N(�CH

��CH

��CO

��CH

�)�)�)�]�


(CDCl�) �

�: 7.23 (12H, bt, e, k), 3.58 (48H, s, q), 3.31 (24H, bm, f, l), 2.95 (8H, bt,.g),

2.75—2.85 (52H, m, a, b, c, h, i), 2.63 (32H, bt, o), 2.45 (32H, bt, n), 2.25 (16H, bt, m);��CNMR (CDCl

�) �

�: 173.15 (d), 172.55 (j), 171.95 (p); Mass spectrum (FAB):m/z


N

NHO

O

NH2

NH2NHN NH

N

N

NH

NH2

NH

NH2

O

O

O

O

NH

NH

N

O

O

NH

N

NH

N

NH

NH

O

O

O

O

NH2

NH2

NH

N

N

NHNH2

NHNH2

O

O

N

N

NHO

O

H2N

H2NNH NNH

N

N

NH

H2N

NH

H2N

O

O

O

O

NH

NH

N

O

O

NH

N

NH

N

NH

NH

O

O

O

O

H2N

H2N

NH

N

N

NHH2N

NHH2N

O

O

N

NHO

N

N

O

NH

NHO

O

NHN

NHO

NO

NH

O

OCH3

N

OCH3

OO OCH3

NOCH3

ONH

N

O OCH3

OCH3

O

N

O

OCH3

OCH3O

NH

N

ONH

OOCH3

NOCH3

O

NH

O

OCH3

N

OCH3O

NH

NH

NO

OCH3

OCH3O

NH

N

O

OCH3OCH3

O

NNH

O

N

N

O

O

O

N O

O NH

O

NH O

N

N

O

NH

NHO

O

NH N

NHO

NO

NH

O

H3CO

N

H3CO

OOH3CO

NH3CO

ONH

N

OH3CO

H3CO

O

N

O

H3CO

H3COO

NH

N

ONH

OH3CO

NH3CO

O

NH

O

H3CON

H3CO O

NH

NH

NO

H3CO

H3CO O

NH

N

O

H3COH3CO

O

NNH

O

NN

O

O

O

NO

ONH

O

[6]

[7]

Scheme 3



H2N—C�H

�—NH

�97 2808 2809

H2N—C�H

—NH

�92 2822 2823

H2N—C�H

�—NH

�93 2836 2837

H2N—C�H

��—NH

�96 2850 2851

H2N—CH

��—NH

�92 2863 2864

Analytical data for dendri-PAMAM(NH�Me)

�.

2809 (MH), 2830 (MNa); Elemental analysis: C��H

��N

�O

��Calcd (%)

C, 53.9; H, 8.1; N, 12.9. Found (%) C, 53.7; H, 8.8; N, 13.2.

3.6 PREPARATION OF AMINE TERMINATED PAMAMDENDRIMER; [NH2–(CH2)2–6–NH2]; dendri-PAMAM (NH2)16;[6]

To a vigorously stirred solution of 1,2-diaminoethane (107 g, 118 ml, 1.781 mol)in methanol (150 ml), at 0°C under nitrogen, was added a solution of (G� 1.5);dendri-PAMAM(CO

�Me)

�; [5] (10 g, 0.004 mol) in methanol (30 ml). The

addition was controlled such that the temperature did not rise above 40°C. Themixture was stirred at room temperature for 96 h, after which time no estergroups were detectable by NMR spectroscopy. The methanol was removed byvacuum distillation at � 40°C, and the excess 1,2-diaminoethane was removedby azeotropic distillation using a mixture of toluene and methanol (9: 1). Theremaining toluene was removed by azeotropic distillation with methanol andfinally the methanol removed under vacuum (10�� mm Hg, 50°C, 48 h) to givethe amine terminated G� 2.0 dendrimer as a pale yellow oil (10.9 g, 94%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

�N(�CH

� CH

��CO�NH�CH

��C

H�N(�CH

��CH

��CO

��CH

�)�)�)�]�

Spectral characterization: IR v��/cm��: 3350 (NH

�); �H NMR (CDCl

�) �

�: 8.01

(28H, bm, e, k, q), 3.19—3.45 (56H, bm, f, l, r), 2.61—2.81 (116H, bm, a, b, c, h, i, n, o),2.98—2.93 (24H, bm,.g, m), 2.45 (32H, bt, t), 2.23 (32H, bp, s); ��CNMR (DMSO)��: 171.65 (d), 171.45 (j), 171.34 (p); Mass spectrum (FAB): m/z 3255 (M—H);

Elemental analysis: C��H

��N

��O

��Calcd (%) C, 52.4; H, 8.9; N, 24.9. Found

(%) C, 47.2; H, 9.7; N, 21.5.

3.7 PREPARATION OF ESTER TERMINATED PAMAMDENDRIMER; [NH2–(CH2)2–6–NH2]; (G=2.5);dendri-PAMAM(CO2Me)32; [7]

A solution of (G� 2); dendri-PAMAM(NH�)�; [6] (10 g, 0.003mol) inmethanol

(20ml) was added to a stirred solution of methylacrylate (10.6 g, 11ml, 0.123mol)


in methanol (20 ml), under nitrogen, over a period of 2 h. The final mixture wasstirred at 0°C for 1 h and then allowed to warm to room temperature and stirredfor a further 24 h. The solvent was removed under reduced pressure at 40°C andthe resultant pale yellow oil vacuum dried (10��mmHg, 50°C) overnight to givethe final product (15.6 g, 84%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

�N(�CH

� CH

��CO�NH�CH

��C

H�N(�CH

��CH

��CO�NH�CH

��CH

�N(�CH

��CO

�CH

�)�)�)�)�]�

Spectral characterization: IR v��/cm��: 1700 (C——O); �H NMR (CDCl

�) �

�: 7.26

(28H, bm, e, k, q), 3.62 (96H, s, w), 3.29—3.41 (56H, bm, f, l, r), 2.77—2.56 (56H,bm,.g, m, s), 2.25—2.45 (116H, bm, a, b, c, h, i, n, o); ��C NMR (CDCl

�) �

�: 177.34

(d), 173.07 (j), 172.32 (p), 171.51 (v); Mass spectrum (FAB): m/z 5978 (M-29);Elemental analysis: C

��H

��N

��O

��Calcd (%) C, 53.9; H, 8.1; N, 13.5. Found

(%) C, 51.3; H, 8.4; N, 13.6.

3.8 PREPARATION OF HYDROXY TERMINATED PAMAMDENDRIMER; [NH2-(CH2)2–6-NH2]; (G= 1.0);dendri-PAMAM(OH)12; [8]

An oven-dried flask, with a septum capped nitrogen inlet, was charged with asolution of (G� 0.5); dendri-PAMAM(CO

�Me)

�; [1] precursor (2.5 g, 6.2

mmol) in anhydrous dimethyl sulfoxide (10 ml). A mixture of Tris (tri-hy-droxymethyl aminoethane) (3.76 g, 0.031mol) and anhydrous potassium carbon-ate (2.7 g, 0.031 mol) was added to the suspension. The solution was heated in aparaffin oil bath maintained at 40°C for 96 h. After filtration the excess solventwas removed by vacuum pump (10�� mm Hg, 50°C). The resulting thick, whiteoil was dissolved in a minimum quantity of distilled water and precipitated withpropanone. The suspension was cooled in the freezer, and the solid filtered anddried in a vacuum oven (10��mmHg, 40°C) to give the hygroscopic terminateddendrimer as a white powder (4.5 g, 95%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHC(CH

��OH)

�)�]�

Spectral characterization: IR v��/cm��: 1635 (C——O); �HNMR (DMSO) �

�: 7.56

(4H, bt, e), 3.47 (24H, s, f), 2.65 (8H, t, b), 2.52 (4H, bt, a), 2.29 (8H, t, c); ��CNMR(CDCl

�) �

�: 172.86 (d), 50.25 (f), 50.21 (b), 35.62 (a), 30.21 (c); Mass spectrum

(FAB): m/z 762 (MH).

3.9 PREPARATION OF HYDROXY TERMINATED PAMAMDENDRIMER; [NH2-(CH2)2-6-NH2]; (G=2.0);dendri-PAMAM(OH)24; [9]

An oven-dried flask, with a septum-capped nitrogen inlet, was charged with asolution of (G� 0.5); dendri-PAMAM(CO

�Me)

�; [3] (5 g, 4.2 mmol) in anhyd


Synthesis of Polyhydroxy Terminated PAMAM Dendrimers

dendri-PAMAM(CO2Me)8

[3]

[9]

O

N

OMe

N

O

OMe

MeO

O

MeO

O

N

NHO

ONH

OH

OH

OH

N

OH

OH

OH

NHO

ONH

N

HO

HO

HO

HO

HO

HO

NHO

NHO

O

NH

OH

OH

OH

HO OHOH

N

NHO

N

NHO

O

NH

OH

OH

OH

HO OHOH

N

NHO

NHO

O

NH

HO

HO

HO

OHHOHO

N

NHO

N

NHO

O

NH

HO

HO

HO

OHHOHO

N

[1]

[8]

K2CO3

(Tris-)

K2CO3, (Tris-)

Scheme 4

rous dimethyl sulfoxide (20 ml). A mixture of Tris (tri-hydroxymethyl amino-ethane) (5.1 g, 0.042 mol) and anhydrous potassium carbonate (5.7 g, 0.042 mol)was added to the suspension. The solution was heated in a paraffin oil bathmaintained at 40°C for 96 h. After filtration the excess solvent was removed byvacuum pump (10��mmHg, 50°C). The resulting thick, white oil was dissolvedin a minimum quantity of distilled water and precipitated with propanone. Thesuspension was cooled in the freezer, and the solid filtered and dried in a vacuum


Dendrimer [core] %Yield MW FAB-Ms

H2N—C�H

�—NH

�99 1918 1919 (MH)

H2N—C�H

—NH

�95 1932 1931 (M H)

H2N—C�H

�—NH

�96 1946 1947 (MH)

H2N—C�H

��—NH

�91 1960 1998 (M 38)

H2N—CH

��—NH

�98 1974 1974 (M)

Analytical data for dendri-PAMAM(OH)��.

oven (10�� mm Hg, 40°C) to give the hygroscopic terminated dendrimer as awhite powder (6.2 g, 82%).

Note: Same procedure can be used when varying the central core unit from 2C to6C.

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

�N

(�CH� CH

��CO�NHC(�CH

��OH)

�)�)�]�


(DMSO) ��: 7.85 (12H, bt, e, k), 4.98 (24H, bs, m), 3.55 (48H, s, l), 3.18 (8H, bm,.f),

2.73 (20H, bm, a, b, g), 2.43 (16H, bt, h), 2.32—2.15 (24H, m, i, c); ��C NMR(DMSO) �

�: 174.25 (d), 62.15 (f); Mass spectrum (FAB): m/z 1919 (MH), 1941

(MNa); Elemental analysis: C��H

��N

��O

��Calcd (%) C, 48.8; H, 7.9; N,

13.1. Found (%) C, 49.9; H, 8.2; N, 14.1.

3.10 PREPARATION OF HYDROXY TERMINATED PAMAMDENDRIMER; [NH2-(CH2)2–6-NH2]; (G=3.0);dendri-PAMAM(OH)48; [10]

An oven-dried flask, with a septum-capped nitrogen inlet, was charged with asolution of (G� 1.5); dendri-PAMAM(CO

�Me)

�; [5] (3.1 g, 1.1 mmol) in an-

hydrous dimethyl sulfoxide (10 ml). A mixture of Tris (tri-hydroxymethylaminoethane) (2.3 g, 0.019 mol) and anhydrous potassium carbonate (2.6 g, 0.019mol) was added to the suspension. The solution was heated in a paraffin oil bathmaintained at 40°C for 96h. After filtration the excess solvent was removed byvacuum pump (10��mmHg, 50°C). The resulting thick, white oil was dissolvedin a minimum quantity of distilled water and precipitated with propanone. Thesuspension was cooled in the freezer, and the solid filtered and dried in a vacuumoven (10�� mm Hg, 40°C) to give the hygroscopic terminated dendrimer as awhite powder (3.9 g, 83%).

(�CH��CH

�)[N(�CH

��CH

��CO�NHCH

��CH

�N(�CH

� CH

��CO�NH�CH

��C

H�N(�CH

��CH

��CO�NHC(�CH

��OH)

�)�)�)�]�

Spectral characterization: IR v��/cm��: 1600 (C——O); �HNMR (DMSO) �

�: 8.15


Dendrimer [core] %Yield MW FAB-Ms

H2N–C�H

�—NH

�83 4232 4248 (M 16)

H2N—C�H

—NH

�96 4246 4247 (M H)

H2N—C�H

�—NH

�91 4260 4259 (M H)

H2N—C�H

��—NH

�82 4274 4269 (M 5)

H2N—CH

��—NH

�85 4288 4287 (M H)

Analytical data for dendri-PAMAM(OH)��.

(28H, bm, e, k, q), 4.84 (48H, bs, s), 3.55 (96H, s, r), 3.35 (24H, bm,.f, l), 2.75 (56H,bm, g, h, m, n), 2.53 (32H, bt, o), 2.45 (24H, bm, c, i), 2.25 (12H, bm, a, b); ��CNMR (DMSO) �

�: 173.12 (d), 172.88 (j), 171.18 (p); Mass spectrum (FAB): m/z

4248 (M 16); Elemental analysis: C��H

��N

��O

�Calcd (%) C, 48.9; H, 7.9;

N, 13.9. Found (%) C, 51.2; H, 7.2; N, 13.2.

dendri-PAMAM(CO2Me)16

[5]

[10]

K2CO3, (Tris)

NHO

NHO

N

NHO

NH

O O

NHOH

OH OH

HO

HOHO

N

NH

ON NH

O

ONH

OH

OH

OH

OH

OH

OH

N

NHO

NH

O O

NHOH

OH OH

HO

HOHO

N

NH

ON NH

O

ONH

OH

OH

OH

OH

OH

OH

N

NHO

NHO

N

NHO

NH

OO

NHHO

HOHO

OH

OH OH

N

NH

ONNH

O

ONH

HO

HO

HO

HO

HO

HO

N

NHO

NH

OO

NHHO

HOHO

OH

OH OH

N

NH

ONNH

O

ONH

HO

HO

HO

HO

HO

HO

N

Scheme 5


4 REFERENCES

1. Buhleier, E., Wehner, W. and Vogtle, F. Synthesis, 155—58 (1978).2. Moors, R. and Vogtle, F. Chem. Ber., 126, 2133—2135 (1993).3. Worner, C. and Mulhaupt, R. Angew. Chem. Int. Ed. Engl., 32(9), 1306—1308 (1993).4. Tomalia, D. A., Baker, H., Dewald, J., Hall, M., Kallos, G., Martin, S., Roeck, J.,Ryder, J. and Smith, P. Polym. J. (Tokyo), 17, 117—32 (1985).

5. Tomalia, D. A., Baker, H., Dewald, J., Hall, M., Kallos, G., Martin, S., Roeck, J.,Ryder, J. and Smith, P. Macromolecules, 2466—2468 (1986).

6. Smith, P. B., Martin, S. J., Hall, M. J. and Tomalia, D. A. A characterization of thestructure and synthetic reactions of polyamidoamine ‘STARBURST“’ polymers inMitchell, J. (ed.),Appl.Polym.Analysis.Characterization, Hanser Publishers,Munich,Vienna, New York, pp. 357—385 (1987).

7. Tomalia, D. A., Naylor, A. M. and Goddard III, W. A. Angew. Chem., 102(2), 119—57(1990); Angew. Chem. Int. Ed. Engl., 29(2), 138—175 (1990).

8. Padias, A. B., Hall, H. K. Jr, Tomalia, D. A. and McConnell, J. R. J. Org. Chem., 52,5305—5312 (1987).


dendrimers and other dendritic polymers (frechet/dendrimers) || laboratory synthesis of...

Documents