Synthesis and characterization of fluorescent poly(aromatic amide) dendrimers

Synthesis and Characterization of Fluorescent

Poly(aromatic amide) Dendrimers

Francesca Aulenta,^†Michael G. B. Drew,^†Alison Foster,^‡Wayne Hayes,*^,†Steven Rannard,^‡

David W. Thornthwaite,^‡David R. Worrall,^§and Tristan G. A. Youngs^†

School of Chemistry, The University of Reading, Whiteknights, Reading RG6 6AD, United Kingdom,

Unilever Research and Development, Port Sunlight Laboratory, Quarry Road East,

Bebington, Wirral CH63 3JW, United Kingdom, and Department of Chemistry, Loughborough University,

Loughborough, Leicestershire LE11 3TU, United Kingdom

w.c.hayes@reading.ac.uk

Received July 15, 2004

The synthesis of a series of poly(aromatic amide) dendrimers up to the second generation is described

herein. The AB₂building block used throughout the synthesis of the dendrimers was the allyl ester

of 3,5-diaminocinnamic acid, which has been synthesized from 3,5-dinitrobenzoic acid in good yield

with use of a four-step procedure. Dendron synthesis was achieved via a convergent approach with

use of a sequence of deprotection/coupling steps. Two commercially available alcohols, ^L-menthol

and citronellol, were coupled to the AB₂monomer by using an alkyl diacid spacer and two core

units; 1,7-diaminoheptane and tris(2-aminoethyl)amine have been used to produce the final

dendrimers. Characterization was carried out by NMR and IR spectroscopies, MALDI-TOF mass

spectrometry, GPC, and DSC. The novel monomer and dendritic derivatives exhibited a strong

fluorescence emission in the visible region (λ ≈ 500 nm) of the spectrum and a weak emission in

the near-infrared (λ ≈ 850 nm) upon excitation in the near-UV region. The fluorescence emission

characteristics were found to be solvent and dendrimer generation dependent.

Introduction

spacers into the polymer backbone that then separate the

rigid polyamide moieties. Although this method improves

the processability of the polyamide material, the desir-

able mechanical properties suffer as a consequence.

The incorporation of branched structures³has also

been proposed to disrupt the polyamide chain alignments

and ultimately lead to a reduction of the semicrystalline

nature of these systems.^2,4For example, Kim reported⁵

the preparation of the first hyperbranched poly(aromatic

amide)s via homopolymerization of AB₂monomers in the

form of the amine diacid chlorides. The resultant hyper-

branched poly(aromatic amide)s possessed excellent solu-

bility characteristics in organic solvents such as N,N-

dimethylformamide, N-methylpyrrolidinone, and N,N-

dimethylacetamide. Dendritic poly(aromatic amide)s have

Linear aromatic polyamides exhibit high tensile

strength, elasticity, and high melting points and are thus

suited for use as high-performance fiber materials.¹These

properties are attributable to the rigidity of the polymer

backbone and to the presence of polar groups which give

rise to dipolar interactions and the formation of extended

hydrogen bonding networks between aligned polymer

chains. However, the semicrystalline nature of aromatic

polyamides often renders them insoluble in common

organic solvents and hence these polymers are difficult

to process.²One approach to circumvent the problem of

poor processability has been the introduction of flexible

* To whom correspondence should be address. Phone: +44-118-378-

6491. Fax: +44-118-378-6331.

^†The University of Reading.

(2) Hay, G.; Mackay, M. E.; Hawker, C. J. J. Polym. Sci., Part B:

Polym. Phys. 2001, 39, 1766.

(3) de Gennes, P. G.; Hervet, H. J. Phys. Lett. 1983, 44, L-351.

(4) Seiler, M. Chem. Eng. Technol. 2002, 25, 237.

(5) Kim, J. H. J. Am. Chem. Soc. 1992, 114, 4947.

^‡Port Sunlight Laboratory.

^§Loughborough University.

(1) Stevens, M. P. Polymer Chemistry, an Introduction, 3rd ed.;

Oxford University Press: New York, 1999.

Published on Web 11/26/2004

J. Org. Chem. 2005, 70, 63-78

63

Aulenta et al.

also been investigated in the light of the interesting

physical properties of dendrimers⁶sa notable develop-

ment in this field was reported⁷by Miller and Neenan

in 1990, who described the use of the convergent ap-

proach⁸to construct a poly(aromatic amide) dendrimer

from 5-nitroisophthaloyl dichloride. Feast et al. have

reported⁹an alternative synthesis of dendrimers of this

type via a related convergent method. Since these early

studies, numerous dendritic poly(aromatic amide) sys-

tems that feature modifications within the main poly-

(aromatic amide) backbone have been constructed by

employing a variety of synthetic approaches.^10,11For

example, incorporation of a variety of linker moieties

(such as aliphatic and amino acid units,^12,13esters,¹⁴

ethers,^15,16and urea linkages¹⁷) has been utilized to

improve further the solubility and viscosity characteris-

tics of these systems.

The use of cinnamic acids in dendrimer synthesis has

been reported by several research groups.^18,19For ex-

ample, Wang et al. described¹⁸the synthesis of cin-

namoyl-coated PAMAM dendrimers and the subsequent

photocyclization of the cinnamoyl residues by irradiation

with UV light to obtain cyclobutane derivatives on the

dendrimers’ outer shell. Neubert et al. have outlined¹⁹

the solid-phase synthesis of polyamide dendrimers up to

the second generation that have potential applications

in MALDI-TOF mass spectrometric analysis.

infrared (λ ≈ 850 nm) upon excitation in the near-UV

region. The fluorescence emission characteristics were

found to be solvent dependent, indicating a strong

dependence of solvent polarity and hydrogen bonding

character on both the excited-state energies and the

nonradiative relaxation rates in these compounds.

Results and Discussion

Synthesis of the Poly(aromatic amide) Den-

drimers. The cinnamic acid derivative 3,5-diaminocin-

namic acid 1 was chosen as a suitable building block for

the construction of a novel series of poly(aromatic amide)

dendrimers. However, the selection of a convergent

approach to these dendrimers via selective coupling

between the orthogonal amine and carboxylic acid func-

tionalities necessitated the use of protecting group chem-

istries. Initial studies encompassed the use of ethyl or

tert-butyl esters as the protecting groups for the acid

functionality. However, selective hydrolysis of these

protecting groups was found not to be compatible with

the convergent dendrimer synthesis and led to degrada-

tion of the monomer. In light of these results, the allyl

ester protecting group was utilized. This protecting group

has been shown to be stable under mild basic or acidic

conditions and can be cleaved readily with high selectiv-

ity by an allyl-transfer reaction in the presence of a

palladium catalyst and a nucleophilic allyl acceptor or

hydride transfer agents.²⁰The fully protected/masked

monomer 2 was obtained in two synthetic steps from the

commercially available 3,5-dinitrobenzoic acid 3 (Scheme

1). This synthetic route involved the selective reduction

of 3,5-dinitrobenzoic acid 3 to 3,5-dinitrobenzaldehyde 4

via a one-pot reduction-oxidation process with borane-

dimethyl sulfide (BMS) followed by treatment with

pyridinium chlorochromate (PCC).²¹The resultant alde-

hyde 4 was then reacted with allyl diethylphosphono-

acetate under Wadsworth-Horner-Emmons conditions

to achieve the dinitrocinnamate 2 in 67% yield.²²

The dinitrocinnamate 2 was isolated as single white

crystals that were subjected to X-ray crystallographic

analysis (see Figure 1a). Reduction of the two nitro

groups was achieved with tin(II) chloride²³in a mixture

of THF/H₂O 50:50 to afford the desired 3,5-diaminocin-

namic acid allyl ester 5 in good yield (85%) as yellow

crystals that were also subjected to X-ray crystallographic

analysis. Solid-state analysis revealed clearly that, in

contrast to the dinitrocinnamate 2, in which the phenyl

ring and the allyl ester moiety were not coplanar, the

extensive conjugation of diaminocinnamate 5 was main-

tained throughout the structure by adopting a coplanar

conformation (Figure 1b). This result is in agreement

with the solid-state structures of related cinnamic acid

derivatives reported in the literature,²⁴whereby the

phenyl and the carboxyl groups are almost always

coplanar. However, the solid-state structure of 3,5-

In this paper we describe the synthesis, characteriza-

tion, and photophysical properties of a series of novel

poly(aromatic amide) dendrimers that are based upon the

branched repeat unit 3,5-diaminocinnamic acid. These

dendritic systems were found to be soluble in a wide

range of organic solvents and exhibited a strong fluores-

cence emission in the visible region (λ ≈ 500 nm) of the

spectrum in addition to a weaker emission in the near-

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64 J. Org. Chem., Vol. 70, No. 1, 2005

Fluorescent Poly(aromatic amide) Dendrimers

FIGURE 1. (a) Two views of the solid-state structure of the 3,5-dinitrocinnamic acid allyl ester 2. (b) Two views of the solid-state

structure of the 3,5-diaminocinnamic acid allyl ester 5. (Atom labels: clear circles, medium carbon, small hydrogen; hashed circles,

large oxygen, medium nitrogen).

SCHEME 1. Synthesis of 3,5-Diaminocinnamic Acid Allyl Ester 5, a Novel AB₂Monomer

dinitrocinnamic acid reported²⁵by Desiraju et al. exhib-

ited a 28° intramolecular twist between carboxy and

aromatic groups. Interestingly, this compound was found

to crystallize as an O-H‚‚‚O dimer wherein the hydrogen-

bonded molecules are related by a 2-fold rotation axis

rather than by an inversion centersmore typical for this

class of compounds. The diaminocinnamate 5, a novel

AB₂monomer, was then employed successfully as the key

building block in the convergent synthesis of the desired

poly(aromatic amide) dendrimers.

The solubility of the dendritic systems was a major

requirement to obtain materials that could be further

modified and processed under a wide range of reaction

conditions. It was envisaged that the synthesis of the

monomer-linker-solubilizing group as the first step in the

convergent synthesis of the dendrons would improve the

solubility of the aromatic amide systems and render the

synthesis facile. Bulky terpene derived units (citronellol

and ^L-menthol, respectively) were thus coupled to the

spacer molecule chosen, succinic acid, via an ester link-

age.²⁶The ester bond was obtained by ring opening

succinic anhydride under basic conditions thus affording

a transparent oil 6 and a white solid 7 in yields of 90%

and 95%, respectively. The carboxylic acid derivatives 6

and 7 were then reacted onto the amine groups of

monomer 5, thereby leading to the first generation

dendrons 8 and 9 respectively with ester groups at the

periphery and at the focal point. Synthesis of the dendron

C₂-[G-1]-CO₂Allyl 8 involved the use of a combination of

the coupling reagents 1-[3-(dimethylamino)propyl]-3-

ethylcarbodiimide hydrochloride (EDCI) and 4-hydroxyaza-

benzotriazole (HOAt)²⁷and high yields (ca. 90%) were

obtained although complete conversion of the starting

materials required significant reaction times (up to 4

(26) Cotterill, A. S.; Gill, M.; Milanovic, N. M. J. Chem. Soc., Perkin

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Commun. 1991, 1239.

J. Org. Chem, Vol. 70, No. 1, 2005 65

Aulenta et al.

SCHEME 2. Synthesis of the First Generation Dendrons 8-11

SCHEME 3. Proposed Succinimide Formation

under Basic Conditions

days). More efficient coupling of 6 with the diaminocin-

namate 5 was obtained when benzotriazol-1-yloxytris-

(dimethylamino)phosphonium hexafluorophosphate (BOP)

was used in acetonitrile.²⁸As a consequence the use of

the BOP coupling agent was adopted in the synthesis of

the dendron M₂-[G-1]-CO₂Allyl 9 and excellent yields (up

to 98%) were obtained (Scheme 2).

The cleavage of the allyl ester at the dendron focal

point of dendron 8 was attempted initially with Pd(PPh₃)₄

and morpholine in THF at room temperature.²⁹Under

these conditions morpholine behaves as a reversible allyl

scavenger thereby promoting the reductive elimination

of Pd⁰with subsequent formation of the byproduct N-allyl

morpholine. However, when subjected to these conditions

detrimental degradation of the starting material 8 was

observed after a short period (ca. 1 h), while insignificant

cleavage of the allyl ester occurred. An improvement was

observed when the more stable palladium source, Pd-

(OAc)₂, was used in the presence of PPh₃; however, the

yield of the C₂-[G-1]-CO₂H 10 was poor (27%) and

significant decomposition of the monomer was again

observed. A closer understanding of this phenomenon was

obtained by evaluating the effect of the base upon the

substrate by stirring a solution of the dendron 8 in the

presence of morpholine in THF at room temperature.

Thin layer chromatographic analysis revealed a progres-

sive decrease in the concentration of the starting material

8 with the simultaneous increase in concentration of

citronellol. Therefore, it was proposed that the base was

responsible for the deprotonation of the amide proton that

in turn triggered an intramolecular nucleophilic conden-

sation onto the other carboxyl unit of the succinate

moiety with the result of the elimination of citronellol

as the leaving group (Scheme 3). Kunz et al.³⁰have

observed similar substrate decomposition during the

cleavage of allyl groups from dipeptides. Therefore, the

base-sensitivity of dendron 8 encouraged the trial of

milder deprotection conditions. Some of the first allyl

scavenger systems used in palladium-catalyzed allylic

cleavage were formic acid or ammonium formate.³¹Under

these conditions, allyl cleavage for the dendron 8 occurred

smoothly with no evidence of detrimental side reactions.

A range of palladium catalysts was examined to optimize

this deprotection procedure (see Table 1) and the use of

Pd(OAc)₂afforded the optimum results. This optimized

allyl protection/deprotection method at the focal point of

the aromatic amide dendrons proved to be an efficient

(28) Bodanszky, M.; Bodanszky, A. The Practice of Peptide Synthesis,

2nd Ed.; Springer Manual Lab., 1994.

(29) Kunz, H.; Waldmann, H. Angew. Chem., Int. Ed. Engl. 1984,

23, 71.

(30) Kunz, H.; Waldmann, H.; Unverzagt, C. Int. J. Peptide Protein

Res. 1985, 26, 493.

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66 J. Org. Chem., Vol. 70, No. 1, 2005

Fluorescent Poly(aromatic amide) Dendrimers

TABLE 1. The Different Reaction Conditions Employed

To Cleave Selectively the Allyl Ester Functionality of the

Dendron C₂-[G-1]-CO₂Allyl 8

The dendrimers were constructed from [G-0] to [G-2]

by the coupling of each dendritic wedge to either bifunc-

tional or trifunctional central core units. The synthesis

of the simple zero generation species was carried out by

direct coupling of the citronellol/^L-menthol-spacer moi-

eties to the central units to afford simple aliphatic

skeletons. In contrast, however, the higher generation

dendritic species all featured highly conjugated polyaro-

matic structures. The syntheses of the zero generation

dendrimers possessing a bifunctional core unit were

carried out with EDCI/HOAt as the coupling agent and

co-reagent, respectively. The products were isolated as

either a solid (C₂-[G-0]₂-C 16) or as oil (M₂-[G-0]₂-C 17)

in good yields (55-86%) following purification via column

chromatography. Synthesis of the zero generation with

the trifunctional core C₃-[G-0]₃-N 18 and M₃-[G-0]₃-N 19

was also achieved in respectable yields (41-70%).

Synthesis of the first generation dendrimers was

carried out initially with EDCI/HOAt as the coupling

reagent system, but the yields were very poor. In

particular, the synthesis of M₄-[G-1]₂-C 20 was achieved

in only 10% yield while formation of M₆-[G-1]₃-N 21 was

not observed even after prolonged reaction times. Amides

possess high rotational barriers around the amide C-N

bond and thereby “lock” the conformation of bulky

dendritic structures rendering the coupling step very

difficult.³⁵However, use of more efficient coupling re-

agents such as BOP afforded M₄-[G-1]₂-C 20 as a white

solid in excellent yield (96%) and M₆-[G-1]₃-N 21 as a pale

yellow solid in moderate yield (48%) over a prolonged

reaction time (48 h). The BOP reagent was also used in

the synthesis of C₄-[G-1]₂-C 22 and C₆-[G-1]₃-N 23. These

dendrimers were obtained after purification by column

chromatography as pale yellow solids in acceptable yields

(98% and 28%, respectively), in agreement with the

results obtained for the series of ^L-menthol first genera-

tion dendrimers (Scheme 5). Synthesis of the second-

generation dendrimers was achieved by using the cou-

pling reagent combination of HATU/HOAt leading to the

desired dendrimers C₈-[G-2]₂-C 24 and M₈-[G-2]₂-C 25.

However, in the case of these bulkier and more rigid

dendrimers successful isolation of the pure products

required the use of repetitive silica gel column chroma-

tography.

entry

catalyst

P[PPh₃]₄

Pd(OAc)₂, PPh₃

Pd[PPh₃]₄

Pd(dba)₂, PPh₃

Pd(OAc)₂, PPh₃

base

solvent

yield, %

1²⁹

2³²

3³³

4

morpholine

HCO₂NH₄

THF

27

56

47

74

5

synthetic strategy and was, therefore, employed to gener-

ate the desired poly(aromatic amide) dendrimers bearing

either citronellol or ^L-menthol as the peripheral groups.

The synthesis of M₂-[G-1]-CO₂H 11 was carried out

according to the procedures described in the case of the

synthesis of C₂-[G-1]-CO₂H 10. Cleavage of the allyl

group of 9 was achieved with Pd(OAc)₂or Pd(dba)₂in the

presence of PPh₃and ammonium formate in reasonable

yield (from 45% to 64%). Interestingly, the reaction yields

were lower than those reported for the allyl cleavage of

8, and the optimum results were obtained when Pd(dba)₂

was employed.

Synthesis of citronellol and L-menthol second genera-

tion dendrons C₄-[G-2]-CO₂Allyl 12 and M₄-[G-2]-CO₂-

Allyl 13 was carried out by coupling the dendrons 10 and

11 with monomer 5. BOP was used initially as the

coupling reagent. However, the poor yields and prolonged

reaction times observed in the coupling of the cinnamate

5 with 10 and 11 suggested the use of more active

coupling agents such as O-(7-azabenzotriazol-1-yl-)-

N,N,N′,N′-tetramethyluronium hexafluorophosphate,

(HATU) (a so-called “second generation” uronium cou-

pling reagent).³⁴Uronium salts of this type are employed

widely in peptide chemistry for amide bond formation in

solution or in the solid phase; however, there are only a

few examples reported in polyamide dendrimer synthe-

sis.¹⁵The use of HATU in the presence of HOAt allowed

the successful synthesis of the second generation den-

drons as white solids in excellent yields (69% in the case

of C₄-[G-2]-CO₂Allyl 12 and 95% in the case of M₄-[G-2]-

CO₂Allyl 13). Treatment of these compounds under the

palladium-promoted allyl cleavage conditions (vide supra)

led to the formation of the desired dendrons 14 and 15

as pale yellow solids in reasonable yields (39-69%)

(Scheme 4).

Molecular Modeling Studies. Although dendrimers

are represented typically as symmetrical, globular struc-

tures with the end groups evenly distributed in the outer

shell, several theoretical studies have investigated the

end group positions, potential intermolecular inter-

actions, and dendritic conformations under vacuum and

in different solvent types.³⁶Knowledge of the dendritic

architecture is of great importance to establish and “tune”

the physical properties of the macromolecule. Bhalgat

and Roberts, for example, have carried out molecular

dynamics studies³⁷on a series of PAMAM dendrimers

up to the third and fourth generation and demonstrated

that as the molecular size increased the structures

adopted more dense and spherical conformations.

In this study, the electronic structure of the first

generation dendrimer C₆-[G-1]₃-N 23 was investigated

A range of catalyst systems was tested to achieve

optimum allyl cleavage conditions for the second genera-

tion dendrons and the results are reported in Table 2.

Cleavage of the allyl group from M₄-[G-2]-CO₂Allyl 13

with a combination of Pd(PPh₃)₄and ammonium formate

led to higher yield (69%) of the desired acid product than

when the reaction was performed on M₂-[G-1]-CO₂Allyl

9 (64%). There was no definite trend to describe the

reactivity of the allyl scavenger catalysts as each allyl-

protected dendron required different catalyst combina-

tions to attain the optimum cleavage of the carboxylic

acid focal point protecting group.

(32) Gronquist, M. R.; Meinwald, J. J. Org. Chem. 2001, 66, 1075.

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J. Org. Chem, Vol. 70, No. 1, 2005 67

Aulenta et al.

SCHEME 4. Synthesis of the Second Generation Dendrons

TABLE 2. Different Catalytic Systems Used for the

Cleavage of the Allyl Ester of Second Generation

Dendrons (12 and 13)

methods. Several conformers located in this manner

suggested that the system may exhibit C₃symmetry, and

atomic coordinates were adjusted in order that the

molecular framework contained this symmetry. Without

this approximation, any ab initio calculations on the

system become rather unfeasible. In these studies, a

stable conformation in which the dendrimer assumed a

“spheroidal” structure was calculated (Figure 2), whereby

the flexible citronellol aliphatic arms were backfolded and

the aromatic rings are twisted by approximately 45° with

respect to each other. This twisting of the arms and the

rigidity of the conjugated double bond places the aromatic

rings at a distance of 13.3 Å from each other, which

disfavor intramolecular interactions between the π-sys-

tems of the cinnamate residues.⁴¹

Characterization of the Polyaromatic Dendrons

and Dendrimers: Solubility Properties of the Den-

drons and the Dendrimers. An important character-

istic of dendritic molecules is the high solubility in a large

number of organic solvents, thereby permitting improved

processability characteristics and a wider range of ap-

plications than their linear polymeric analogous. Several

studies have compared^15,42,43the physical and chemical

properties of different dendrimers with their linear

substrate

catalyst

additives, solvent yield, %

C₄-[G-2]-CO₂Allyl 12 Pd(PPh₃)₄

Pd(OAc)₂

THF

PPh₃, THF

THF

PPh₃, THF

67

58

69

39

56

M₄-[G-2]-CO₂Allyl 13 Pd(PPh₃)₄

Pd(OAc)₂

Pd(dba)₂

with ab initio methods in conjunction with preliminary

molecular mechanics (MM) treatment. The structure was

built within Cerius2³⁸and was subjected to MM energy

minimization, using the Universal Force Field³⁹with

calculated QEq atomic charges.⁴⁰Several successive

“agitations” to this configuration were made, each con-

sisting of a short, elevated-temperature (1000 K) molec-

ular dynamics (MD) simulation in the NVT ensemble in

the gas phase, accompanied by subsequent MM energy

minimizations. These stages are employed to locate a

suitable low-energy conformation of the system, such that

the intended ab initio minimization has a suitable

starting point. Conformational analysis cannot be used

to this end as a consequence of the high flexibility of the

molecule, resulting in the number of possible conformers

being too numerous to digest with current computational

(41) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112,

5525.

(42) Wooley, K. L.; Fre´chet, J. M. J.; Hawker, C. J. Polymer 1994,

35, 4489.

(37) Bhalgat, M. K.; Roberts, J. C. Eur. Polym. J. 2000, 36, 647.

(38) Cerius2; Molecualr Simulations/Biosym Inc., San Diego, CA,

1998.

(39) Rappe´, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, W. A.;

Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024.

(40) Rappe´, A. K.; Goddard, W. A. J. Phys. Chem. 1991, 95, 3358.

(43) (a) Hawker, C. J.; Malmstro¨m, E. E.; Frank, C. W.; Kampf, J.

P. J. Am. Chem. Soc. 1997, 119, 9903. (b) Hay, G.; Mackay, M. E.;

Hawker, C. J. J. Polym. Sci., Part B: Polym. Phys. 2001, 39, 1766.

68 J. Org. Chem., Vol. 70, No. 1, 2005

Fluorescent Poly(aromatic amide) Dendrimers

SCHEME 5. Synthesis of the Zero, First, and Second Generation Dendrimers 16-25

polymer analogues and found enhanced solubility proper-

ties for the branched systems.

for these substrates in nonpolar solvents such as n-

hexane. The dendrons bearing a carboxylic acid at the

focal point were soluble in polar solvents such as THF,

ethanol, and acetone. First generation dendrimers ex-

hibited similar solubility properties to the dendrons with

protected focal points, although increasing the generation

limited the solubility to solvents such as acetone, DMF,

and DMSO. At low concentrations, the C₈-[G-2]₂-C 24

dendrimer was also soluble in THF and ethanol. A

comparison of the solubility properties of these systems

with analogous dendrimers built via a divergent ap-

proach and possessing nitro groups at the periphery⁴⁴

confirmed that the introduction of flexible and more

lipophilic groups on the external layer of the dendritic

structure disrupted partially the network of noncovalent

interations such as hydrogen bonding and π-π stacking,

and thus enhanced greatly the solubility of these poly-

amide dendrimers.

Different solubility properties were found in the poly-

amide dendrons (8-15) and the dendrimers (16-25). In

general, dendrons bearing an ester at the focal point were

soluble in solvents of medium to high polarity such as

halogenated solvents, THF, alcohols, acetone, and amidic

solvents. However, very low solubilities were observed

NMR Spectroscopic Analysis. NMR spectroscopy

provides useful information toward the structural iden-

tification of dendritic macromolecules as well as the

degree of purity and in some extent furnishes important

information upon the solution state properties of these

polyamide dendrimers. As the molecular weights of the

dendrons and dendrimers synthesized were not especially

FIGURE 2. Molecular model of C₆-[G-1]₃-N 23 generated with

molecular mechanics energy minimization and ab Initio

calculations.

(44) Aulenta, F. Ph.D. Thesis, The University of Reading, 2003.

J. Org. Chem, Vol. 70, No. 1, 2005 69

Aulenta et al.

1

FIGURE 3. The H NMR spectra of C₈-[G-2]₂-C 24 Recorded at 40 °C.

high (606 to 2997 Dalton) the ¹H NMR resonances of the

protons of these compounds were well resolved. Several

important features emerged from the H NMR spectro-

interesting featureswhen the spectrum was recorded at

400 MHz and at 40 °C the resonances of the protons

(j and o, Figure 3) corresponding to the trans olefins

appeared unexpectedly as two sets of overlapped doublets

whereas when the spectrum was recorded at 250 MHz

and at room temperature these resonances appeared as

normal doubletssa more common feature for trans-

disubstituted olefins. These differing multiplicities may

be rationalized as a “twist” of the dendritic structure to

generate units that are no longer symmetrical in nature

and therefore experience different microenvironments.

MALDI-TOF Mass Spectrometry, GPC, and DSC

Characterization. MALDI-TOF mass spectrometry was

used⁴⁶to analyze the polyamide dendrons and den-

drimers described above. The optimum spectra were

obtained when R-cyano-4-hydroxycinnamic acid was used

as the matrix and the detector was used in linear mode.

Under these conditions all the compounds analyzed

afforded excellent signal/noise ratios without the addition

of cationization agents. However, in conjunction with the

molecular ion peak, the corresponding sodiated and

potassiated adducts were also detected (these cations are

present as impurities in glassware), indicating relatively

high cation affinities of the dendritic molecules. At high

laser powers, molecular ion-matrix aggregates were also

observed. MALDI-TOF mass spectrometric analysis was

also used to assess the relative purity of the molecules

synthesized, as in all of the dendrimers described peaks

attributable to fragmentation of the sample were not

observed (Figure 4).

1

scopic analysis. A significant solvent effect was observed

on the series of dendrons and dendrimers bearing cit-

ronellol surface groups. Replacement of strongly hydro-

gen bonding solvents such as d₆-DMSO with CDCl₃led

to significant peak broadening, noticeable particularly in

the case of the resonances of the protons in close

proximity with the N-H bonds. Upon changing the

solvent from d₆-DMSO to CDCl₃, considerable shifts to

higher fields of the NH protons were also observed (0.7

ppm for the more external NH) caused by the removal of

the hydrogen bonding interactions with the solvent.⁴⁵

This phenomenon is also indicative of self-aggregation

(e.g., via π-π aromatic stacking, hydrogen bonding)

generated by the presence of a “poor” solvent, whereby

the highly polar dendritic structures tend to aggregate

to minimize the interactions with the solvent. In contrast,

in a “good” solvent (such as d₆-DMSO), the dendrons and

dendrimers were solvated readily and aggregation phe-

1

nomena occurred only to a small extent.¹³The H NMR

spectra of the polyamide dendrimers and dendrons of

different generations revealed significant similarities in

the chemical shifts of the aliphatic moieties. However, it

was noted that as the generation number increased the

signals of the protons of the external aromatic rings and

of the conjugated double bonds were subjected to upfield

shifts (0.2 ppm) (Figure 3). Stoddart and co-workers¹⁶and

Chow and co-workers¹³reported similar upfield shifts of

proton atoms of peripheral units of polyamide dendrimer

systems, which were attributed to microenviromental

changes within the dendritic structure. The chemical

shifts of the olefinic protons of C₈-[G-2]₂-C revealed an

Gel permeation chromatography (GPC) was also car-

ried out to further confirm the purity of all dendrons and

(46) (a) Hayes, W.; Freeman A. W.; Fre´chet, J. M. J. Polym. Mater.

Sci. Eng. 1997, 77(2), 136. (b) Yu D.; Vladimirov N.; Fre´chet J. M. J.

Macromolecules 1999, 32, 5186.

(45) Kessler, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 512.

70 J. Org. Chem., Vol. 70, No. 1, 2005

Fluorescent Poly(aromatic amide) Dendrimers

FIGURE 4. MALDI-TOF mass spectra of the citronellol dendritic family.

dendrimers and to analyze the structural changes that

occur by varying the generation number and degree of

branching of the core. GPC analyses of all the dendritic

molecules were carried out with THF as the eluent and

the retention times were compared to a set of polystyrene

standards used as calibrants, to determine the average

molecular weight (M_w) of the species eluted.^43a,47The GPC

traces obtained for the citronellol and ^L-menthol den-

drimer families are shown in Figure 5. A similar trend

was observed in the two families of dendrimers, whereby

the M_wwas found to be greater than the predicted values

in the case of dendrimers possessing the bifunctional core.

However, increasing the multiplicity of the core from two

to three resulted in an increase in the retention time,

hence M_wvalues that were closer to the predicted values

for [G-0]₃-N but lower than that determined for the

[G-1]₃-N dendrimer. This behavior indicates clearly that

the dendrimers possessing a bifunctional core assumed

a more open conformation in solution, resembling a

random coil, whereas the dendrimers with a trifunctional

core assumed a more condensed conformation in solution.

Although this feature is found commonly in dendritic

(47) (a) Hawker, C. J.; Wooley, K. L.; Fre´chet J. M. J. J. Am. Chem.

Soc. 1993, 115, 4375. (b) Moreno-Bondi, M. C.; Orellana, G.; Turro, N.

J.; Tomalia, D. A. Macromolecules 1990, 23, 912. (c) Naylor, A. M.;

Goddard, W. A., III; Kiefer, G. E.; Tomalia, D. A. J. Am. Chem. Soc.

1989, 111, 2339.

J. Org. Chem, Vol. 70, No. 1, 2005 71

Aulenta et al.

FIGURE 5. GPC traces of the citronellol and L-menthol dendritic families. (Note: Linear polymers and dendritic systems possess

very different retention volumes and therefore the use of linear polystyrene calibrants will generate lower molecular weights for

the dendritic samples.^43a,47

)

systems, whereby the generation number of surface

groups increases exponentially eventually leading to a

globular conformation,⁴⁸in the dendrimers described this

phenomenon was observed at low generations, and most

likely arose as a consequence of the rigidity of the

dendritic amide backbone. GPC analysis of C₈-[G-2]₂-C

24 in THF revealed evidence for self-aggregation and

interaction of the dendrimers with the solid support. The

chromatograms possessed not only a long tail at high

molecular weight but also shoulders corresponding to

high molecular weight species were clearly visible. This

behavior can be attributed to the poor solubility of these

dendrimers in THF, which resulted in the formation of

aggregates (note that MALDI-TOF mass spectrometric

and NMR spectroscopic analyses confirmed the purity of

this compound).

Differential scanning calorimetric analysis (DSC) (Sup-

porting Information) revealed the melting ranges for the

majority of the dendritic species bearing citronellol

residues at the peripheral surfaces (with the exception

of C₃-[G-0]₃-N 18, which is an oil) thereby indicating

partial crystallinity of these compounds. The zero gen-

eration aliphatic species exhibited a very low melting

point (44.4-43.4 °C) as expected by consideration of the

very flexible structure. However, the higher generation

species possessed much higher and broader melting

ranges, generally between 170 and 250 °C, as a conse-

quence of the progressive increased rigidity of the com-

pounds and the presence of intermolecular hydrogen

bonding. Interestingly, although the two series of den-

drons featured an identical cinnamic amide backbone,

significant differences in the melting point characteristics

were observed. For example, the dendron C₂-[G-1]-CO₂-

Allyl 8 exhibited a broad melting range at high temper-

ature (240-260 °C), typical of amide-type compounds,

whereas the ^L-menthol dendron derivative M₂-[G-1]-CO₂-

Allyl 9 revealed a well-defined melting point at low

temperature (50.3-52.3 °C). The highly crystalline na-

ture of the citronellol-derived dendrimers was demon-

strated in particular by C₄-[G-2]-CO₂Allyl 12, which

possessed a very sharp melting peak between 259 and

261 °C. The corresponding dendron C₄-[G-2]-CO₂H 14

that featured a carboxyl group at the focal point exhibited

a broad melting peak at a higher temperature (258-296

°C) as a consequence of the extended hydrogen bonded

network involving the acid moiety and the amide groups

of the dendritic backbone. However, very different melt-

ing point characteristics were exhibited by the series of

L-menthol dendrimerssthese systems were amorphous

solids that did not exhibit detectable melting points.

Furthermore, these compounds did not reveal any glass

transitions (T_g) within the interval examined even after

repeated scans and cooling to low temperatures.

Steady-State and Time-Resolved Fluorescence

Spectroscopic Studies. In parallel with the synthetic

development of novel dendrimers, attention has shifted

in recent times more toward novel applications of these

perfectly hyperbranched species. Although efficient pho-

tocycloaddition reactions in the solid state⁴⁹and photo-

isomerization of the double bond when electronically

excited by UV radiation in solution⁵⁰of species of this

type are well documented, cinnamic acid derivatives do

not tend to exhibit fluorescence emissions. However, Jia

and co-workers have reported¹⁸recently that cinnamoyl

shell-modified PAMAM dendrimers did exhibit strong

fluorescence emissions.

To verify if the novel cinnamic acid derivatives devel-

oped in this synthetic study revealed similar photochemi-

cal characteristics, preliminary absorption and emission

spectroscopic studies of the 3,5-diaminocinnamic acid

allyl ester 5 and the dendritic derivatives (8-25) that

feature the diaminocinnamate moiety within the building

block were carried out. Steady-state fluorescence experi-

ments were carried out by irradiating the molecules at

different wavelengths to evaluate the dependence of the

emission with the excitation wavelength used. Five

solutions of concentrations ranging from 0.0001 to 0.0150

mM were investigated and the emission characteristics

analyzed in a solvent of low polarity such as hexane, and

higher polarity such as acetonitrile (a hydrogen bond

acceptor solvent) and methanol (a hydrogen bond donor

and acceptor solvent). It was envisaged that these three

parameters would furnish the information necessary to

identify the photophysical characteristics of the species

(49) Choen, M. D.; Schmidt, G. H. J. Reactivity of Solids; Elsevier:

Amsterdam, The Netherlands, 1961; p 556.

(50) Curme, H. G.; Natale, C. C.; Kelley, D. J. J. Phys. Chem. 1967,

71, 767.

(48) Dvornic, P. R.; Tomalia, D. A. Macromol. Symp. 1995, 98, 403.

72 J. Org. Chem., Vol. 70, No. 1, 2005

Fluorescent Poly(aromatic amide) Dendrimers

FIGURE 7. The fluorescent emission of M₆-[G-1]₃-N 21

recorded in hexane and methanol, upon excitation at λ ) 273

nm.

FIGURE 6. Normalized emission spectra of 3,5-diaminocin-

namic acid allyl ester 5 recorded in hexane and methanol at

λ_ex) 273 nm.

fluorescence band. This behavior was consistent through-

out the series of [G-1] dendrons and dendrimers 8-23

(Figure 7snote some artifacts appearing in the spectrum

arising from second-order reflections in the emission

gratings from the excitation wavelength (at 546 nm) and

from the main emission band, appearing around 800 nm;

careful use of filters has established that there are no

emission bands in these regions), although increasing the

generation number up to two yet again affected this

emission characteristic (vide infra).

The second generation dendrons 12-15 revealed a

drastic decrease in both the emission intensity and

lifetime, with, for example, the lifetime for M₄-[G-2]-CO₂-

Allyl 13 in methanol solution being below the time

resolution of the apparatus used (<100 ps). However, the

dendrimer C₈-[G-2]₂-C 24 exhibited again an increase in

fluorescence. Detailed investigations of the photophysical

properties of these dendritic poly(aromatic amide) ma-

terials are currently underway and the results of these

studies will be reported soon.

Conclusions. The syntheses of a series of novel poly-

(aromatic amide) dendrimers have been described in this

article. The dendrimers were based on a novel AB₂

monomer, 3,5-diaminocinnamic acid, and were con-

structed via convergent approach with the dendritic

growth starting from the peripheral surface groups (the

terpene solubilizing moieties), followed by addition of the

internal branched layers and final coupling with a

multifunctional core. The solubilizing units used, cit-

ronellol and ^L-menthol, were conjugated on the dendritic

surface by means of a spacer, whose presence introduced

a degree of flexibility in the dendritic backbone as

indicated by molecular modeling studies. The dendrimers

were synthesized up to the second generation by coupling

of the dendrons to two types of cores, a bifunctional and

a trifunctional core, respectively. These compounds ex-

hibited good solubility properties in a variety of organic

solvents such as DMF, DMSO, CH₂Cl₂, CHCl₃, MeOH,

acetone, and THF. Furthermore, this novel building block

and its dendritic derivatives displayed interesting fluo-

rescence emissions in the visible region (λ ≈ 500 nm) of

the spectrum upon excitation at 273 nm. The fluorescence

spectra and emission lifetimes of the monomer were

involved and to determine whether molecular aggrega-

tion also played an important role in the emission

properties. 3,5-Diaminocinnamate 5 was irradiated at

three different wavelengths, two of which correspond to

absorption maxima (210 and 330 nm) with the third (273

nm) corresponding to the λ_maxof unsubstituted cinnamic

acid. The emission spectra were recorded between 200

and 950 nm. The spectra obtained were not normalized

and the fluorimeters’ sensitivity was adjusted for each

analysis to obtain responses within the scale limits,

therefore, in many cases direct and precise comparison

of the emission intensities was not possible. However,

interesting results were obtained when the diaminocin-

namate 5 was excited at 273 nm (Figure 6). In the hexane

solutions, the fluorescence emission was detectable even

in the case of very diluted solutions (10^-4mM) and the

intensity increased almost 6-fold for the solution with a

concentration of 0.015 mM. In this solvent a major

emission with a maximum at 425 nm was observed.

However, this emission decreased in intensity by 50% and

a bathochromic shift of 75 nm was observed in aceto-

nitrile, and almost complete fluorescence quenching was

revealed in methanolic solution. These large solvent

shifts may be indicative of profound solvent interactions

with the excited states, resulting in significant excited

state stabilization. Additionally the possibility of excimer

formation in these solvents cannot be ruled out, and is

the subject of ongoing investigations. Fluorescence life-

time data show a decrease in lifetime in deoxygenated

solution from approximately 4.8 ns in hexane solution

to 1.74 nm in methanol solution. The concomitant

decrease in fluorescence yield is indicative of the solvent-

promoting nonradiative relaxation in compound 5 as the

solvent polarity and hydrogen bonding ability increase.

The effect of different substituents on the benzene ring

of the molecule has proven to have a significant impact

on the fluorescent properties. The presence of two nitro

groups in the meta position quenched the radiative

emission completely, whereas interconversion of the

amine groups into amides with alkyl chains of different

rigidity not only increased the fluorescence yield but also

resulted in a hypsochromic shift for the main maximum

J. Org. Chem, Vol. 70, No. 1, 2005 73

Aulenta et al.

187.6 ppm. IR ν_maxcm^-13075, 1706, 1625, 1541. CI-MS:

C₇H₄N₂O₅, m/z calcd for (M - H)⁺195.00, found (M - H)⁺

195.00.

found to be strongly solvent dependent. Increasing the

dendritic generations also generally resulted in a de-

crease in emission lifetime and quantum yield.

Synthesis of 2. To a suspension of NaH (0.65 g, 16.00

mmol) in dry THF (20 mL) was added allyl diethylphospho-

noacetate (4.00 g, 15.90 mmol) in a dropwise fashion and the

mixture was stirred at room temperature for 15 min. A solution

of 3,5-dinitrobenzaldehyde 4 (2.00 g, 10.00 mmol) in dry THF

(5 mL) was then added and the reaction gently refluxed under

argon for 12 h. The progress of the reaction was monitored by

TLC analysis (CH₂Cl₂-EtOAc 98:2, R_f0.68). The excess NaH

was quenched by careful addition of a few drops of methanol

and then by addition of water (10 mL). The product was then

extracted in EtOAc (3 × 20 mL), washed with brine, dried

(MgSO₄), and filtered and the solvent was removed under

reduced pressure to leave the crude product, which was further

purified by column chromatography (CH₂Cl₂-EtOAc 98:2) to

afford a light brown solid (0.15 g, in 54% yield, mp 147-149

°C). ¹H NMR (250 MHz, CDCl₃) δ 4.23 (2 H, d, ³J_HH) 5.8 Hz),

5.28 (2 H, m), 5.90 (1 H, m), 6.96 (1 H, d, ³J_{HH Trans}) 16.0 Hz),

7.75 (1 H, ³J_{HH Trans}) 16.0 Hz), 8.61 (2 H, s), 8.97 (1 H, s) ppm.

¹³C NMR (62.8 MHz, CDCl₃) δ 66.3, 119.4, 119.7, 124.4, 127.7,

131.9, 138.5, 140.0, 149.4, 165.31 ppm. IR ν_max2350, 1708,

1650, 1538 cm^-1. CI-MS: C₁₂H₁₀N₂O₆, m/z calcd for M⁺278.05,

found M⁺278.05. Anal. Calcd for C₁₂H₁₀N₂O₆: C 51.80, H 3.62,

N 10.06. Found: C 51.22, H 3.63, N 9.91.

Experimental Section

Sample Preparations for UV-Vis and Fluorescence

Spectroscopies. General procedure: Samples were pre-

pared by carefully transferring a fixed aliquot of sample into

a volumetric flask (100 mL, or otherwise stated) and diluting

to volume with HPLC-grade hexane, acetonitrile, or methanol,

respectively, to obtain 0.5000 mM solutions (or otherwise

stated). The solutions were subjected to ultrasound irradiation

for a period of 10 min prior to use. Known aliquots of the

0.5000 mM stock solutions were transferred carefully into

volumetric flasks and diluted to volumes to obtain solutions

of concentrations 0.0150, 0.0100, 0.0050, 0.0010, and 0.0001

mM, respectively. Each flask was subjected to ultrasound

irradiation for 10 min prior to use.

Molecular Modeling Study. Dendrimer C₆-[G-1]₃-N 23

was built and subjected to initial molecular mechanics energy

minimization with the Universal force-field, using the Cerius2

software.³⁸Geometry optimizations were carried out on the

system with the Gaussian03 software. From the symmetric,

pseudo-low-energy configuration generated via the described

molecular mechanics (MM)/molecular dynamics (MD) treat-

ment, a preliminary low-level ab initio calculation was per-

formed with the STO-3G basis set at the Hartree-Fock level.

Once suitable convergence parameters had been achieved, the

calculation was restarted employing the 3-21G basis set, this

being followed by a third calculation at the 6-31G(d) level. All

optimizations were carried out in the gas phase at a standard

temperature and pressure of 298.15 K and 1 atm. C₃symmetry

was imposed at all points in the optimization.

Synthesis of 4. Part 1: Synthesis of 3,5-Dinitroben-

zoyloxyboroxine. 3,5-Dinitrobenzoic acid 3 (6.36 g, 30.00

mmol) and dry THF (38 mL) were placed into a dry, round-

bottomed flask equipped with a septum inlet, magnetic stirring

bar, and a reflux condenser, under a stream of argon. The

mixture was stirred vigorously and borane-dimethyl sulfide

(BMS) (3.06 mL, 30.00 mmol) was added dropwise from a

syringe. Following the addition of an initial aliquot of BMS

(1-1.5 mL), when the gas evolution ceased, the mixture was

heated under gentle reflux to complete the evolution of gas.

The remaining BMS was added at such a rate as to maintain

a gentle reflux. Following completion of the addition, the

mixture was heated under reflux for 12 h. The solvent and

the dimethyl sulfide were then removed under reduced pres-

sure and THF (50 mL) was added to dissolve the residue. The

progress of the reaction was monitored by TLC analysis (CH₂-

Cl₂-EtOAc 80:20, R_f0.77). 3,5-Dinitrobenzoyloxyboroxine was

not isolated but was oxidized directly in the second step to

yield the desired compound.

Part Two: Oxidation of 3,5-Dinitrobenzoyloxyborox-

ine to 3,5-Dinitrobenzaldehyde. To a well-stirred solution

of PCC (7.80 g, 36.00 mmol) in dry THF (50 mL) was added

dropwise the solution of 3,5-dinitrobenzoyloxyboroxine in THF

(50 mL). The stirred mixture was heated under reflux over-

night and then diluted with CH₂Cl₂(50 mL). The supernatant

and the solid residue were then filtered through Florisil (50.00

g) contained in a sintered-glass funnel. The filtrate was

concentrated under reduced pressure and the crude product

purified by column chromatography (CH₂Cl₂-hexane 90:10)

to yield a yellow powder (3.10 g, 52% yield, mp 78-80 °C (lit.⁵¹

mp 76-80 °C)). The progress of the reaction was monitored

by TLC analysis (CH₂Cl₂-EtOAc 90:10, R_f0.79). ¹H NMR (250

MHz, CDCl₃) δ 8.98 (2 H, s), 9.23 (1 H, s), 10.15 (1 H, s)

ppm.¹³C NMR (62.8 MHz, CDCl₃) δ 123.7, 129.1, 138.8, 149.9,

Synthesis of 5. To a solution of 3,5-dinitrocinnamic acid

allyl ester 2 (1.20 g, 4.32 mmol) in THF (10 mL) and distilled

water (10 mL) was added SnCl₂(9.00 g, 48.10 mmol) and the

reaction was heated under reflux for 2 h. The reaction profile

was monitored by TLC analysis (CHCl₃-EtOH 9:1, R_f0.27).

After cooling to room temperature, the solution was poured

onto ice contained in a beaker and then treated with a solution

of 5% NaHCO₃in water (200 mL) until the pH was 7-8. EtOAc

(80 mL) was then added and the white precipitate filtered off.

The product was then extracted with EtOAc (3 × 100 mL).

The combined organic layers were then dried (MgSO₄) and

filtered and the solvent was removed under reduced pressure

to leave the crude product, which was further purified by

column chromatography (CHCl₃-EtOH 99:1) to afford the

desired product as a yellow solid (0.80 g, 86% yield, mp 70-

1

72 °C). H NMR (250 MHz, CDCl₃) δ 3.57 (4 H, s), 4.63 (2 H,

3

d, J_HH) 5.6 Hz), 5.26 (2 H, m), 5.88 (1 H, m), 5.95 (1 H, s),

3

6.20 (2 H, s), 6.30 (1 H, d, J_{HH Trans}) 15.9 Hz), 7.48 (1 H, d,

³J_{HH Trans}) 15.9 Hz) ppm. ¹³C NMR (62.8 MHz, CDCl₃) δ 64.0,

102.7, 104.6, 116.4, 117.3, 131.3, 135.2, 144.6, 146.8, 165.8

ppm. IR ν_max3500, 3361, 2315, 1701, 1631, 1597 cm^-1

.

CI-MS: C₁₂H₁₄N₂O₂, m/z calcd for (M + H)⁺219.11, found (M

+ H)⁺219.11. Anal. Calcd for C₁₂H₁₄N₂O₂: C 66.04, H 6.47, N

12.83. Found: C 66.05, H 6.54, N 12.69.

Synthesis of 6. A mixture of citronellol (4.06 g, 26.00

mmol), succinic anhydride (3.00 g, 30.00 mmol), and DiPEA

(4.50 mL, 26 mmol) in ether (10 mL) was stirred for 2 days at

room temperature. Conversion of the reaction was followed by

TLC analysis (CHCl₃-EtOH 90:10, R_f0.27). The solvent was

removed under reduced pressure, and the residue dissolved

in CH₂Cl₂(50 mL) and washed with an aqueous solution of

5% w/w citric acid (2 × 30 mL). The organic layer was dried

(MgSO₄) and filtered and the solvent was removed under

reduced pressure to give the crude product that was purified

by column chromatography (CHCl₃-EtOH 98:2) to afford 6 as

a transparent oil (6.00 g, 90% yield). ¹H NMR (250 MHz,

CDCl₃) δ 0.86 (3 H, d, ³J_HH) 6.4 Hz), 1.17 (1 H, m), 1.37 (4 H,

m), 1.56 (3 H, s), 1.64 (3 H, s), 1.94 (2 H, m), 2.48 (4 H, m),

4.01 (2 H, m), 5.07 (1 H, m) ppm. ¹³C NMR (62.8 MHz, CDCl₃)

δ 18.0, 19.7, 25.7, 26.1, 29.3, 29.8, 35.7, 37.3, 63.8, 124.9, 131.7,

172.5, 178.7 ppm. IR ν_max2924, 1739, 1716, 1436 cm^-1. CI-

MS: C₁₄H₂₄N₂₂O₃₃, m/z calcd for (M + H)⁺257.17, found (M +

H)⁺257.17.

Synthesis of 8. To a solution of succinic acid mono(3,7-

dimethyl-oct-6-enyl) ester 6 (7.00 g, 27.30 mmol), 3,5-diami-

nocinnamic acid allyl ester 5 (0.30 g, 1.35 mmol), and DiPEA

(51) Siggins, J. E.; Larsen, A. A.; Ackermann, J. H.; Carabateas, C.

D. Organic Syntheses: Wiley: New York, XXXX; Collect. Vol. VI, p

529.

74 J. Org. Chem., Vol. 70, No. 1, 2005

Fluorescent Poly(aromatic amide) Dendrimers

3

(5.18 mL, 27.00 mmol) in dry CH₃CN (70 mL) was added

benzotriazol-1-yloxytris(dimethylamino)phosphonium hexaflu-

orophosphate (BOP) (10.13 g, 27.00 mmol) (0.68 g, 3.50 mmol)

and the reaction was left stirring at room temperature

overnight. The reaction profile was monitored by TLC analysis

(CHCl₃-EtOH 9:1, R_f0.74). The reaction was quenched by the

addition of water (70 mL) and the desired product was

extracted with CHCl₃(3 × 30 mL). The organic layers were

dried (MgSO₄) and filtered and the solvent was removed under

reduced pressure to leave the crude product that was purified

further by column chromatography (CHCl₃-EtOH 98:2) to

afford a yellowish waxy material (6.10 g, 96% yield). ¹H NMR

d, J_{HH Trans}) 16.0 Hz), 7.66 (1 H, s), 8.37 (2 H, s) ppm. ¹³C

NMR (62.8 MHz, CDCl₃) δ 16.6, 18.3, 24.7, 28.4, 30.4, 34.3,

36.0, 62.7, 112.0, 114.1, 123.5, 130.3, 132.4, 134.0, 137.7, 137.8,

169.4, 170.6, 172.7 ppm. IR ν_max3291, 2963, 2345, 1734, 1701,

1672, 1636, 1555, 1429, 1261 cm^-1. MALDI TOF MS: C₃₇H₅₄-

N₂O₈, m/z calcd for (M + H)⁺655.39, (M + Na)⁺677.38, (M +

K)⁺693.35, found (M + H)⁺655.10, (M + Na)⁺677.90, (M +

K)⁺693.40.

Synthesis of 11. M₂-[G-1]-CO₂Allyl 9 (6.00 g, 8.64 mmol)

was dissolved in THF (100 mL). The solution was then treated

with HCO₂NH₄(6.43 g, 99.40 mmol), PPh₃(1.13 g, 4.34 mmol),

and Pd(dba)₂(1.12 g, 1.94 mmol) and the mixture was heated

under reflux under an argon atmosphere for 8 h. The reaction

was monitored by TLC analysis (CHCl₃-EtOH 98:2, R_f0.52).

The reaction mixture was then cooled and filtered and the

solvent was removed under reduced pressure. The solid residue

was dissolved in EtOAc (50 mL), washed with water (3 × 20

mL), dried (MgSO₄), and filtered and the solvent was removed

under reduced pressure. The progress of the reaction was

monitored by TLC analysis (CHCl₃-EtOH 9:1) and the crude

product purified by column chromatography in gradient elution

(from CHCl₃to CHCl₃-EtOH 95:5) to afford the desired

product as a white solid (3.89 g, 69% yield, mp 198.9-200.9

°C) ([R]²⁰_D-41.00 (c 1 in MeOH)).¹H NMR (250 MHz, CDCl₃)

3

(250 MHz, CDCl₃) δ 0.83 (6 H, d, J_HH) 6.3 Hz), 1.18 (2 H,

m), 1.24 (2 H, m), 1.34 (2 H, m), 1.40 (2 H, m), 1.51 (6 H, s),

1.57 (2 H, m), 1.62 (6 H, s), 1.88 (4 H, m), 2.63 (8 H, m), 4.05

(4 H, m), 4.62 (2 H, d, ³J_HH) 5.6 Hz), 4.99 (1 H, m), 5.20 (2 H,

m), 5.88 (1 H, m), 6.32 (1 H, d, ³J_{HH Trans}) 16.0 Hz), 7.37 (2 H,

3

s), 7.46 (1 H, d, J_{HH Trans}) 16.0 Hz), 7.96 (1 H, s), 8.25 (2 H,

s) ppm. ¹³C NMR (62.8 MHz, CDCl₃) δ 18.0, 19.7, 25.7, 29.6,

29.1, 32.2, 35.7, 36.9, 37.3, 63.9, 65.5, 112.9, 115.1, 118.5, 119.0,

124.9, 131.7, 132.5, 135.9, 139.3, 144.9, 166.8, 170.6, 173.7

ppm. IR ν_max3342, 3090, 1734, 1718, 1639, 1601, 1555 cm^-1

.

CI-MS: C₄₀H₅₈N₂O₈, m/z calcd for 695.42 (M + H)⁺, found (M

+ H)⁺695.42. FAB MS: m/z calcd for (M + Na)⁺717.41, (M +

K)⁺733.38, found (M + Na)⁺717.40, (M + K)⁺733.41.

3

δ 0.68 (6 H, d, J_HH) 6.8 Hz), 0.80 (6 H, d, J_HH) 6.9 Hz),

0.85 (6 H, d, ³J_HH) 6.9 Hz), 0.95 (4 H, m), 1.26 (4 H, m), 1.35

(4 H, m), 1.60 (2 H, m), 1.86 (2 H, m), 2.58 (8 H, m), 4.57 (2 H,

Synthesis of 9. To a solution of succinic acid mono(5-

isopropyl-2-methylcyclohexyl) ester 7 (7.00 g, 27.30 mmol), 3,5-

diaminocinnamic acid allyl ester 5 (0.30 g, 1.35 mmol), and

DiPEA (5.18 mL, 27.00 mmol) in dry CH₃CN (70 mL) was

added BOP (10.13 g, 27.00 mmol) and the reaction was left

stirring at room temperature overnight. The reaction profile

was monitored by TLC analysis (CHCl₃-EtOH 9:1, R_f0.70).

The reaction was quenched by the addition of water (70 mL)

and the desired product was extracted with CHCl₃(3 × 30

mL). The organic layers were dried (MgSO₄) and filtered and

the solvent was removed under reduced pressure to leave the

crude product, further purified by column chromatography

m), 6.31 (1 H, d, ³J_{HH Trans}) 15.9 Hz), 7.44 (1 H, d, ³J_{HH Trans}

)

15.9 Hz), 7.55 (2 H, s), 7.89 (1 H, s), 10.10 (2 H, s) ppm. ¹³C

NMR (62.8 MHz, CDCl₃) δ 16.4, 20.8, 22.1, 23.6, 26.6, 30.2,

31.7, 32.2, 34.5, 40.9, 47.2, 75.2, 112.9, 115.0, 135.6, 138.5,

147.4, 159.8, 165.1, 173.1, 174.5 ppm. IR ν_max3259, 3021, 2869,

1727, 1699, 1657, 1597, 1423, 1293 cm^-1. MALDI-TOF MS:

m/z calcd for (M + Na)⁺677.38, (M + K)⁺693.33, found (M +

Na)⁺677.40, (M + K)⁺693.40.

Synthesis of 12. To a solution of C₂-[G-1]-CO₂H 10 (0.11

g, 0.168 mmol), 3,5-diaminocinnamic acid allyl ester 5 (0.02

g, 0.07 mmol), 4-hydroxyazabenzotriazole (HOAt) (0.02 g, 0.17

mmol), and DiPEA (0.06 mL, 0.34 mmol) in dry CH₃CN (2.5

mL) was added O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetra-

methyluronium hexafluorophosphate (HATU) (0.06 g, 0.17

mmol) and the reaction was left stirring at room temperature

for 24 h. Progress of the reaction was followed by MALDI-

TOF MS and TLC analysis (CHCl₃-EtOH 9:1, R_f0.39). The

reaction was quenched by the addition of water (3 mL) and

the desired product was extracted with CHCl₃(3 × 5 mL). The

organic layers were dried (MgSO₄) and filtered and the solvent

was removed under reduced pressure to leave the crude

product, which was purified further by column chromatogra-

phy (CHCl₃-EtOH 95:5) to afford a white solid (0.07 g, 69%

yield, mp 259-261 °C). ¹H NMR (250 MHz, d₆-DMSO) δ 0.87

(CHCl₃-EtOH 98:2) to afford a yellowish solid (6.23 g, 98%

1

yield, mp 50.3-52.3 °C) ([R]²⁰-46.20 (c 1.00 in CHCl₃)). H

D

3

NMR (250 MHz, d₆-DMSO) δ 0.67 (6 H, d, J_HH) 6.9 Hz),

0.77 (6 H, d, ³J_HH) 6.9 Hz), 0.83 (6 H, d, ³J_HH) 6.9 Hz), 0.91

(2 H, m), 1.26 (4 H, m), 1.38 (4 H, m), 1.60 (4 H, m), 1.81 (2 H,

m), 1.86 (2 H, m), 2.59 (8 H, m), 4.57 (2 H, m), 4.69 (2 H, d,

³J_HH) 5.3 Hz), 5.31 (2 H, m), 6.33 (1 H, m), 6.39 (1 H, d,

³J_{HH Trans}) 15.9 Hz), 7.59 (1 H, d, ³J_{HH Trans}) 15.7 Hz), 7.60 (2

H, s), 7.90 (1 H, s), 10.11 (2 H, s) ppm. ¹³C NMR (62.8 MHz,

d₆-DMSO) 16.5, 20.8, 22.2, 26.0, 29.3, 31.1, 31.4, 34.0, 46.7,

64.9, 73.6, 112.1, 113.6, 118.0, 133.0, 134.6, 140.4, 145.2, 165.8,

170.4, 172.0, 173.7 ppm. IR ν_max3343, 2300, 1726, 1650, 1601,

1555 cm^-1. MALDI-TOF MS: C₃₇H₅₄N₂O₈m/z calcd for (M +

Na)⁺717.41, (M + K)⁺733.38, found (M + Na)⁺717.33, (M +

K)⁺733.30.

3

(12 H, d, J_HH) 6.4 Hz), 1.13 (4 H, m), 1.25 (4 H, m), 1.33 (4

H, m), 1.42 (4 H, m), 1.49 (4 H, m), 1.52 (12 H, s), 1.66 (12 H,

s), 1.94 (4 H, m), 2.66 (16 H, m), 4.09 (8 H, m), 4.76 (2 H, m),

5.09 (4 H, m), 5.39 (2 H, m), 6.05 (1 H, m), 6.52 (1 H, d,

³J_{HH Trans}) 15.9 Hz), 6.90 (2 H, d, ³J_{HH Trans}) 15.6 Hz), 7.54 (2

H, d, J_{HH Trans}) 15.4 Hz), 7.64 (1 H, d, J_{HH Trans}) 15.9 Hz),

7.73 (4 H, s), 7.83 (2 H, s), 7.85 (2 H, s), 8.19 (1 H, s), 10.19 (4

H, s), 10.70 (2 H, s) ppm. ¹³C NMR (62.8 MHz, d₆-DMSO) δ

17.8, 19.5, 25.2, 25.8, 29.2, 31.2, 35.3, 36.8, 62.6, 65.0, 111.3,

112.4, 113.3, 114.1, 118.1, 122.5, 124.9, 130.9, 133.0, 134.9,

135.5, 140.4, 140.6, 140.9, 146.0, 164.0, 165.8, 170.5, 172.6.

IR ν_max3328, 1731, 1716, 1686, 1676, 1614, 1556 cm^-1. MALDI-

TOF-MS: C₈₆H₁₁₈N₆O₁₆, m/z calcd.for M⁺1490.86, (M + Na)⁺

1513.85, (M + K)⁺1529.82, found M⁺1490.01, (M + Na)⁺

1513.01, (M + K)⁺1529.74.

Synthesis of 13. To a solution of M₂-[G-1]-CO₂H 11 (0.60

g, 0.97 mmol), 3,5-diaminocinnamic acid allyl ester 5 (0.90 g,

0.41 mmol), DiPEA (0.3 mL, 1.55 mmol), and HOAt (0. 14 g,

1.00 mmol) in dry CH₃CN (20 mL) was added HATU (0. 38 g,

1.00 mmol) and the reaction mixture was left stirring at room

temperature for 2 days. The progress of the reaction was

Synthesis of 10. C₂-[G-1]-CO₂Allyl 8 (9.30 g, 13.39 mmol)

was dissolved in THF (200 mL). The solution was then treated

with HCO₂NH₄(9.50 g, 152.00 mmol), PPh₃(1.88 g, 7.23

mmol), and Pd(OAc)₂(0.65 g, 2.89 mmol) and the mixture was

heated under reflux under an argon atmosphere for 8 h. The

reaction was monitored by TLC analysis (CHCl₃-EtOH 9:1,

R_f0.23). The reaction mixture was then cooled and filtered

and the solvent was removed under reduced pressure. The

solid residue was dissolved in EtOAc (100 mL), washed with

water (3 × 50 mL), dried (MgSO₄), and filtered and the solvent

was removed under reduced pressure. The progress of the

reaction was monitored by TLC analysis (CHCl₃-EtOH 9:1,

R_f0.23) and the crude product purified by column chromatog-

raphy, using a gradient elution (from CHCl₃-EtOH 98:2 to

CHCl₃-EtOH 20:80), to afford the desired product as a pale

yellow powder (6.50 g, 74% yield). ¹H NMR (250 MHz, CDCl₃)

3

δ 0.84 (6 H, d, J_HH) 6.4 Hz), 1.18 (2 H, m), 1.23 (2 H, m),

1.33 (2 H, m), 1.36 (2 H, m), 1.52 (6 H, s), 1.56 (2 H, m), 1.64

(6 H, s), 1.89 (4 H, m), 2.66 (8 H, m), 4.08 (4 H, m), 5.00 (2 H,

m), 6.23 (1 H, d, ³J_{HH Trans}) 16.0 Hz), 7.17 (2 H, s), 7.32 (1 H,

J. Org. Chem, Vol. 70, No. 1, 2005 75

Aulenta et al.

monitored by TLC analysis (CHCl₃-EtOH 9:1, R_f0.5) and

MALDI-TOF MS. The reaction was then quenched with water

(20 mL) and the product extracted in CHCl₃(3 × 10 mL). The

organic solvent was dried (MgSO₄), filtered, and evaporated

under reduced pressure. The crude product was purified by

column chromatography (CHCl₃-EtOH 96:4) to afford a yel-

31.2, 31.4, 34.0, 38.8, 46.7, 73.6, 111.2, 113.3, 122.6, 135.4,

136.5, 137.5, 140.4, 140.8, 163.9, 170.5, 172.0 ppm. IR ν_max

3430, 2959, 1713, 1631, 1557 cm^-1. MALDI-TOF MS: C₈₃H₁₁₄

-

N₆O₁₆, m/z calcd for (M + Na)⁺1473.82, (M + K)⁺1489.79,

found (M + Na)⁺1473.82, (M + K)⁺1489.79.

Synthesis of 16. To a solution of 1,7-diaminoheptane (0.16

g, 1.25 mmol), succinic acid mono(3,7-dimethyl-oct-6-enyl) ester

6 (0.77 g, 3.00 mmol), HOAt (0.41 g, 3.00 mmol), and N-

methylmorpholine (NMM) (0.33 mL, 3.00 mmol) in dry DMF

(8 mL) was added EDCI (0.58 g, 3.00 mmol) at 0 °C, and the

reaction was left stirring at room temperature for 24 h. The

reaction profile was monitored by TLC analysis (CHCl₃-EtOH

90:10, R_f0.58). The reaction was quenched by the addition of

HCl (1 M, 10 mL) and the desired product was extracted with

CHCl₃(3 × 10 mL). The organic layers were dried (MgSO₄)

and the solvent was removed under reduced pressure to leave

the crude product, whcih was further purified by column

chromatography (CHCl₃-EtOH 96:4) to afford a white solid

(0.65 g, 86% yield, mp 41.4-43.4 °C). ¹H NMR (250 MHz,

CDCl₃) δ 0.84 (6 H, d, ³J_HH) 6.3 Hz), 1.11 (2 H, m), 1.23 (4 H,

m), 1.28 (6 H, m), 1.40 (4 H, m), 1.43 (4 H, m), 1.53 (6 H, s),

1.60 (6 H, s), 1.93 (4 H, m), 2.38 (4 H, m), 2.58 (4 H, m), 3.16

(4 H, m), 4.04 (4 H, m), 5.01 (2 H, m), 5.78 (2 H, m) ppm. ¹³C

NMR (62.8 MHz, CDCl₃) δ 16.6, 18.3, 24.3, 24.7, 25.6, 28.3,

28.4, 28.7, 30.1, 34.3, 35.9, 38.4, 62.3, 123.5, 130.3, 170.3, 172.1

ppm. IR ν_max3326, 2932, 1723, 1640, 1539 cm^-1. CI MS:

C₃₅H₆₂N₂O₆, m/z calcd for (M + H)⁺607.47, found (M + H)⁺

607.47. MALDI-TOF MS: m/z calcd for (M + H)⁺607.47, (M

+ Na)⁺629.45, (M + K)⁺645.42, found (M + H)⁺606.97, (M

+ Na)⁺629.56, (M + K)⁺645.21. Anal. Calcd for C₃₅H₆₂N₂O₆:

C 69.27, H 10.30, N 4.61. Found: C 68.97, H 10.42, N 4.53.

lowish waxy material (0.58 g, 95%) ([R]²⁰-63.90 (c 0.50 in

D

1

CHCl₃)). H NMR (400 MHz, d₆-DMSO) δ ppm 0.70 (12 H, d,

³J_HH) 6.9 Hz), 0.83 (12 H, d, J_HH) 7.0 Hz), 0.89 (12 H, d,

3

³J_HH) 7.0 Hz), 1.06 (12 H, m), 1.32 (8 H, m), 1.64 (8 H, m),

1.88 (8 H, m), 2.64 (16 H, m), 4.62 (4 H, m), 4.75 (2 H, d, ³J_HH

) 5.3 Hz), 5.39 (2 H, m), 6.05 (1 H, m), 6.46 (1 H, d, ³J_{HH Trans}

3

) 16.0 Hz), 6.88 (2 H, d, J_{HH Trans}) 15.5 Hz), 7.51 (2 H, d,

³J_{HH Trans}) 15.5 Hz), 7.51 (1 H, d, ³J_{HH Trans}) 15.8 Hz), 7.73 (4

H, s), 7.82 (2 H, s), 7.83 (2 H, s), 8.17 (1 H, s), 10.18 (4 H, s),

10.56 (2 H, s) ppm. ¹³C NMR (100 MHz, d₆-DMSO) δ 15.7, 20.0,

21.4, 22.4, 25.1, 28.6, 30.3, 30.6, 33.2, 39.6, 45.9, 64.2, 72.8,

110.4, 112.4, 113.3, 117.3, 121.6, 132.2, 134.1, 134.5, 139.6,

139.7, 140.2, 145.0, 163.1, 165.0, 169.6, 171.2 ppm. IR ν_max

3446, 1635 cm^-1. MALDI-TOF MS: C₈₆H₁₁₈N₆O₁₆, m/z calcd

for (M + Na)⁺1513.85, (M + K)⁺1529.82, found (M + Na)⁺

1514.41, (M + K)⁺1529.59.

Synthesis of 14. C₄-[G-2]-CO₂Allyl 12 (0.07 g, 0.05 mmol)

was dissolved in THF (4 mL). The solution was then treated

with HCO₂NH₄(0.03 g, 0.50 mmol) and Pd(PPh₃)₄(0.02 g, 0.01

mmoL) and the mixture was heated under reflux under an

argon atmosphere for 4 h. The reaction mixture was then

cooled and filtered and the solvent was removed under reduced

pressure. The solid residue was dissolved in EtOAc (5 mL),

washed with water (3 × 5 mL), dried (MgSO₄), and filtered

and the solvent was removed under reduced pressure. The

progress of the reaction was monitored by TLC analysis

(CHCl₃-EtOH 9:1, R_f0.25) and the crude product purified by

column chromatography employing a gradient elution (from

CHCl₃-EtOH 95:5 to CHCl₃-EtOH 20:80), to afford the

desired product as a pale yellow solid (0.05 g, 67% yield, mp

Synthesis of 17. To a solution of 1,7-diaminoheptane (0.16

g, 1.25 mmol), succinic acid mono(5-isopropyl-2-methylcyclo-

hexyl) ester 7 (0.77 g, 3.00 mmol), HOAt (0.41 g, 3.00 mmol),

and NMM (0.33 mL, 3.00 mmol) in dry DMF (8 mL) was added

EDCI (0.580 g, 3.00 mmol) at 0 °C, and the reaction was left

stirring at room temperature for 24 h. The reaction profile was

monitored by TLC analysis (CHCl₃-EtOH 90:10, R_f0.59). The

reaction was quenched by the addition of HCl (1 M, 10 mL)

and the desired product was extracted with CHCl₃(3 × 10

mL). The organic layers were dried (MgSO₄) and filtered and

the solvent was removed under reduced pressure to leave a

crude product that was further purified by column chroma-

tography (CHCl₃-EtOH 95:5) to afford the desired product as

1

(broad) 258-296 °C). H NMR (250 MHz, CDCl₃) δ 0.77 (12

3

H, d, J_HH) 6.4 Hz), 1.02 (4 H, m), 1.10 (4 H, m), 1.26 (4 H,

m), 1.39 (4 H, m), 1.45 (12 H, s), 1.48 (4 H, m), 1.53 (12 H, s),

1.79 (4 H, m), 2.52 (16 H, m), 3.99 (8 H, m), 4.99 (4 H, m),

3

6.35 (1 H, d, J_{HH Trans}) 15.5 Hz), 6.80 (2 H, d, J_{HH Trans}

)

3

15.8 Hz), 7.39 (2 H, d, J_{HH Trans}) 15.5 Hz) 7.51 (2 H, d,

³J_{HH Trans}) 15.8 Hz), 7.60 (4 H, s), 7.64 (2 H, s), 7.73 (2 H, s),

7.93 (1 H, s), 10.16 (4 H, s) ppm. ¹³C NMR (62.8 MHz, CDCl₃)

δ 17.8, 19.5, 25.1, 25.8, 29.2, 31.3, 35.3, 36.8, 62.6, 113.1, 113.3,

122.5, 124.9, 129.0, 130.9, 131.9, 135.5, 137.0, 140.4, 140.9,

142.0, 164.0, 165.8, 170.5, 172.6 ppm. IR ν_max3324, 2963, 1716,

1678, 1613, 1425 cm^-1. MALDI-TOF MS: C₈₃H₁₁₄N₆O₁₆, m/z

calcd for (M + Na)⁺1473.82, (M + K)⁺1489.79, found (M +

Na)⁺1473.40, (M + K)⁺1488.3.

a transparent oil (1.00 g, 55% yield) ([R]²⁰-60.4 (c 1.00 in

D

CHCl₃)). ¹H NMR (250 MHz, CDCl₃) δ 0.65 (6 H, d, ³J_HH) 6.9

Hz), 0.80 (2 H, m), 0.81 (12 H, m), 0.87 (4 H, m), 1.25 (8 H,

m), 1.40 (2 H, m), 1.43 (2 H, m), 1.57 (4 H, m), 1.62 (2 H, m),

1.85 (2 H, m), 2.35 (8 H, m), 3.13 (4 H, m), 4.62 (2 H, m) ppm.

¹³C NMR (62.8 MHz, CDCl₃) δ 16.7, 21.1, 22.4, 23.8, 26.6, 27.0,

29.0, 29.8, 30.4, 31.7, 34.6, 39.8, 41.2, 47.3, 75.0, 171.8, 173.1

Synthesis of 15. M₄-[G-2]-CO₂Allyl ester 13 (0.04 g, 0.03

mmol) was dissolved in THF (2.5 mL). The solution was then

treated with HCO₂NH₄(0.02 g, 0.34 mmol) and Pd(PPh₃)₄(0.01

g, 0.01 mmol) and the mixture was heated under reflux under

an argon atmosphere for 4 h. The reaction mixture was then

cooled and filtered and the solvent was removed under reduced

pressure. The solid residue was dissolved in EtOAc (5 mL),

washed with water (2 × 3 mL), dried (MgSO₄), and filtered

and the solvent was removed under reduced pressure. The

reaction was monitored by MALDI-TOF MS and TLC analysis

(CHCl₃-EtOH 9:1, R_f0.2) and the crude product purified by

gradient column chromatography (from CHCl₃-EtOH 85:15

to CHCl₃-EtOH 10:90) to afford a white solid (30.00 mg, 69%

ppm. IR ν_max3303, 2953, 1731, 1649, 1552, 1454 cm^-1

.

CI-MS: C₃₅H₆₂N₂O₆, m/z calcd.for (M + H)⁺607.47, found (M

+ H)⁺607.47. MALDI-TOF MS: (M + Na)⁺629.45, (M + K)⁺

645.42, (M + Na)⁺, found (M + K)⁺629.36, 645.26. Anal. Calcd

for C₃₅H₆₂N₂O₆: C 69.27,, H 10.30, N 4.62. Found: C 68.44, H

10.35, N 4.55.

Synthesis of 18. To a solution of tris(2-ethylamino)amine

(TREN) (0.17 mL, 1.10 mmol), succinic acid mono(3,7-dimeth-

yl-oct-6-enyl) ester 6 (1.00 g, 3.90 mmol), HOAt (0.54 g, 3.90

mmol), and NMM (0.43 mL, 3.90 mmol) in dry DMF (12 mL)

was added EDCI (0.75 g, 3.90 mmol) at 0 °C, and the reaction

was left stirring at room temperature for 24 h. The reaction

profile was monitored by TLC analysis (CHCl₃-EtOH 95:5,

R_f0.49). The reaction was quenched by the addition of HCl (1

M, 12 mL) and the desired product was extracted with CHCl₃

(3 × 10 mL). The organic layers were dried (MgSO₄) and

filtered and the solvent was removed under reduced pressure

to leave the crude product, which was further purified by

column chromatography (CHCl₃-EtOH 98:2) to afford a

transparent oil (0.66 g, 70% yield). ¹H NMR (250 MHz, CDCl₃)

yield, mp (broad) 250-285 °C) ([R]²⁰_D-24.9 (c 0.285 in CHCl₃)).

3

¹H NMR (400 MHz, d₆-DMSO) δ ppm 0.67 (12 H, d, J_HH

)

3

6.9 Hz), 0.78 (12 H, d, J_HH) 7.0 Hz), 0.84 (12 H, d, J_HH

7.0 Hz), 1.00 (8 H, m), 1.22 (4 H, m), 1.30 (12 H, m), 1.59 (8 H,

m), 1.88 (8 H, m), 2.59 (16 H, m), 4.56 (4 H, m), 6.35 (1 H, d,

³J_{HH Trans}) 16.0 Hz), 6.83 (2 H, d, ³J_{HH Trans}) 15.5 Hz), 7.40 (1

3

H, br d), 7.42 (1 H, d, J_{HH Trans}) 15.8 Hz), 7.68 (6 H, s), 7.63

(2 H, s), 8.30 (1 H, s), 10.14 (4 H, s), 10.45 (2 H, s) ppm. ¹³C

3

NMR (100 MHz, d₆-DMSO) δ 16.5, 20.8, 22.2, 23.2, 25.9, 29.4,

δ 0.84 (9 H, d, J_HH) 6.4 Hz), 1.14 (3 H, m), 1.27 (3 H, m),

76 J. Org. Chem., Vol. 70, No. 1, 2005

Fluorescent Poly(aromatic amide) Dendrimers

1.33 (3 H, m), 1.39 (3 H, m), 1.52 (9 H, s), 1.58 (3 H, m), 1.63

(9 H, s), 1.92 (6 H, m), 2.45 (6 H, m), 2.55 (6 H, m), 2.68 (6 H,

m), 3.25 (6 H, m), 4.05 (6 H, m), 5.03 (3 H, m), 6.85 (3 H, m)

ppm. ¹³C NMR (62.8 MHz, CDCl₃) δ 17.7, 19.4, 25.4, 29.3, 29.5,

30.5, 35.4, 37.0, 38.0, 54.3, 63.4, 124.5, 131.4, 172.1, 173.5 ppm.

IR ν_max3290, 3099, 1734, 1651, 1546, 1455 cm^-1. MALDI-TOF

MS: C₄₈H₈₄N₄O₉, m/z calcd for M⁺860.62, (M + Na)⁺883.61,

(M + K)⁺899.59, found M⁺860.19, (M + Na)⁺882.91, (M +

K)⁺898.93. Anal. Calcd for C₄₈H₈₄N₄O₉‚3DMF‚4H₂O: C 59.40,

H 9.88, N 8.51. Found: C 59.18, H 9.61, N 8.61.

in CHCl₃(3 × 10 mL) and washed with brine (3 × 10 mL).

The organic layer was then dried (MgSO₄) and filtered and

the solvent was removed under reduced pressure. The crude

product was purified by column chromatography (CHCl₃-

EtOH 99:1) to afford a white amorphous solid (0.147 g, 48%

yield) ([R]²⁰_D-36.2 (c 0.25 in CHCl₃)). ¹H NMR (400 MHz, d₆-

3

DMSO) δ 0.70 (18 H, d, J_HH) 6.9 Hz), 0.83 (18 H, d, J_HH

)

7.0 Hz), 0.84 (6 H, m), 0.88 (18 H, d, ³J_HH) 7.0 Hz), 0.94 (6 H,

m), 1.04 (6 H, m), 1.27 (12 H, m), 1.30 (12 H, m), 1.42 (12 H,

m), 1.62 (12 H, m), 2.62 (24 H, m), 3.10 (6 H, m), 3.28 (6 H,

m), 4.59 (6 H, m), 6.68 (3 H, d, ³J_{HH Trans}) 15.7 Hz), 7.32 (3 H,

Synthesis of 19. To a solution of TREN (0.17 mL, 1.10

mmol), succinic acid mono(5-isopropyl-2-methylcyclohexyl)

ester 7 (1.00 g, 3.87 mmol), HOAt (0.54 g, 3.90 mmol), and

NMM (0.43 mL, 3.90 mmol) in dry DMF (12 mL) was added

EDCI (0.75 g, 3.90 mmol) at 0 °C, and the reaction was left

stirring at room temperature for 24 h. The reaction profile was

monitored by TLC analysis (CHCl₃-EtOH 90:10, R_f0.60). The

reaction was quenched by the addition of HCl (1 M, 12 mL)

and the desired product was extracted with CHCl₃(3 × 10

mL). The organic layers were dried (MgSO₄) and filtered and

the solvent was removed under reduced pressure to leave the

crude product, whcih was further purified by column chroma-

3

d, J_{HH Trans}) 15.5 Hz), 7.58 (6 H, s), 7.85 (3 H, s), 8.32 (3 H,

s), 10.10 (6 H, s) ppm. ¹³C NMR (100 MHz, d₆-DMSO) δ 17.2,

21.5, 22.9, 23.9, 26.6, 30.1, 31.8, 32.1, 34.7, 38.3, 47.4, 54.6,

74.2, 111.5, 113.7, 123.3, 136.4, 140.0, 141.0, 165.9, 172.7,

172.7 ppm. IR ν_max3349, 1727, 1661, 1618, 1555, 1453 cm^-1

.

MALDI-TOF MS:

C

₁₁₇H₁₇₄N₁₀O₂₁, m/z calcd for (M + H)⁺

2056.29, (M + Na)⁺2078.28, (M + K)⁺2094.25, found (M +

H)⁺2055.96, (M + Na)⁺2078.25, (M + K)⁺2094.49. GPC

(THF): M_w1766, M_n1729, M_w/M_n1.02.

Synthesis of 22. To a solution of C₂-[G-1]-CO₂H 10 (0.21

g, 0.32 mmol) and 1,7-diaminoheptane (0.02 g, 0.14 mmol) in

dry CH₃CN (5 mL) was added BOP (0.15 g, 0.40 mmol)

followed by DiPEA (0.03 mL, 0.15 mmol), and the mixture was

stirred at room temperature for 48 h and the conversion of

the starting material was monitored by TLC (CHCl₃-EtOH

9:1, R_f0.37) and MALDI-TOF MS. The reaction was quenched

by addition of water (5 mL) and the product was extracted in

CHCl₃(3 × 5 mL). The organic layer was then dried (MgSO₄)

and filtered and the solvent evaporated under reduced pres-

sure. The crude product was purified by column chromatog-

raphy (CHCl₃-EtOH 96:4) to afford a pale yellow solid (0.19

g, 98% yield, mp (broad) 240-280 °C). ¹H NMR (250 MHz,

d₆-DMSO) δ 0.82 (12 H, d, ³J_HH) 6.3 Hz), 1.23 (8 H, m), 1.25

(4 H, m), 1.33 (10 H, m), 1.36 (4 H, m), 1.39 (4 H, m), 1.41 (12

H, s), 1.47 (4 H, m), 1.55 (12 H, s), 1.89 (8 H, m), 2.59 (16 H,

m), 3.17 (4 H, m), 4.03 (8 H, m), 5.04 (4 H, m), 6.57 (2 H, d,

³J_{HH Trans}) 15.6 Hz), 7.28 (1 H, d, ³J_{HH Trans}) 15.5 Hz), 7.54 (4

H, s), 7.81 (2 H, s), 8.31 (2 H, s), 10.08 (4 H, s) ppm. ¹³C NMR

(62.8 MHz, d₆-DMSO) δ 17.8, 19.5, 25.1, 25.8, 26.8, 28.9, 29.1,

29.4, 31.2, 35.3, 36.7, 36.8, 62.5, 79.5, 111.0, 113.0, 122.8, 124.9,

130.9, 135.8, 138.7, 140.3, 164.9, 170.3, 172.6 ppm. IR ν_max

3270, 3099, 1735, 1690, 1663, 1617, 1558, 1452 cm^-1. FAB

MS: C₈₁H₁₂₂N₆O₁₄, m/z calcd for (M + Na)⁺1425.89, found (M

+ Na)⁺1425.89. MALDI-TOF MS: m/z calcd for M⁺1402.90,

(M + Na)⁺1425.89, (M + K)⁺1441.87, found M⁺1401.34,

(M + Na)⁺1424.25, (M + K)⁺1440.39. Anal. Calcd for

C₈₁H₁₂₂N₆O₁₄: C 69.30, H 8.76, N 5.98. Found: C 69.20, H 8.73,

N 5.62. GPC (THF): M_w1645, M_n1631, M_w/M_n1.01.

tography (CHCl₃-EtOH 98:2) to afford a transparent oil (0.39

1

g, 41% yield) ([R]²⁰-60.05 (c 1.00 in CHCl₃)). H NMR (250

D

3

MHz, CDCl₃) δ 0.65 (9 H, d, J_HH) 6.9 Hz), 0.80 (3 H, m),

0.82 (18 H, m), 0.98 (6 H, m), 1.31 (3 H, m), 1.35 (3 H, m),

1.57 (6 H, m), 1.72 (3 H, m), 1.84 (3 H, m), 2.43 (12 H, m),

2.63 (6 H, m), 3.27 (6 H, m), 4.59 (3 H, m), 6.87 (3 H, m) ppm.

¹³C NMR (100 MHz, CDCl₃) δ 16.4, 20.7, 22.0, 23.4, 26.2, 29.6,

30.6, 31.4, 34.2, 38.3, 40.9, 46.9, 54.3, 74.6, 172.2, 173.0 ppm.

IR ν_max3291, 2953, 1729, 1651, 1456 cm^-1. FAB MS: C₄₈H₈₄-

N₄O₉, m/z calcd for (M + H)⁺861.63, (M + Na)⁺883.61, found

(M + H)⁺861.63, (M + Na)⁺883.62. MALDI-TOF MS: (M +

H)⁺861.63, found (M + H)⁺863.21. Anal. Calcd for C₄₈H₈₄N₄O₉‚

3H₂O: C 62.99, H 9.91, N 6.12. Found: C 62.78, H 9.35, N

6.10.

Synthesis of 20. To a solution of 1,7-diaminoheptane (0.05

g, 0.40 mmol), M₂-[G-1]-CO₂H 11 (0.65 g, 0.99 mmol), and

DiPEA (0.31 mL, 1.79 mmol) in dry CH₃CN (20 mL) was added

BOP (0.46 g, 1.20 mmol) and the reaction was left stirring at

room temperature for 24 h. The reaction profile was monitored

by TLC analysis (CHCl₃-EtOH 9:1, R_f0.61). The reaction was

quenched by the addition of distilled water (20 mL) and the

product was extracted with CHCl₃(3 × 20 mL). The organic

layers were dried (MgSO₄) and filtered and the solvent was

removed under reduced pressure to leave the crude product,

whcih was further purified by column chromatography (CHCl₃-

EtOH 97:3) to afford a white amorphous solid (0.54 g, 96%

1

yield) ([R]²⁰-35.00 (c 1.00 in CHCl₃)). H NMR (400 MHz,

D

d₆-DMSO) δ 0.66 (12 H, d, ³J_HH) 6.9 Hz), 0.77 (12 H, d, ³J_HH

) 6.9 Hz), 0.85 (4 H, m), 0.88 (12 H, d, ³J_HH) 6.9 Hz), 0.98 (4

H, m), 1.07 (4 H, m), 1.33 (10 H, m), 1.46 (8 H, m), 1.64 (8 H,

m), 1.86 (8 H, m), 2.54 (16 H, m), 3.18 (4 H, m), 4.60 (4 H, m),

Synthesis of 23. To a solution of TREN (0.03 mL, 0.23

mmol) and C₂-[G-1]-CO₂H 10 (0.51 g, 0.77 mmol) in dry CH₃-

CN (10 mL) was added BOP (0.30 g, 0.80 mmol) followed by

DiPEA (0.06 mL, 0.30 mmol). The reaction mixture was left

stirring at room temperature for 4 days, and conversion of the

starting material was monitored by TLC (CHCl₃-EtOH 9:1,

R_f0.66) and MALDI-TOF MS. The reaction was quenched by

addition of water (10 mL), extracted with CHCl₃(3 × 10 mL),

and then washed with brine (3 × 10 mL). The organic layer

was then dried (MgSO₄) and filtered and the solvent was

removed under reduced pressure. The crude product was

purified by column chromatography (CHCl₃-EtOH 99:1) to

afford a white solid (0.13 g, 28% yield, mp (broad) 183-201

°C). ¹H NMR (250 MHz, d₆-DMSO) δ 0.84 (18 H, d, ³J_HH) 6.3

Hz), 1.13 (6 H, m), 1.26 (6 H, m), 1.33 (6 H, m), 1.38 (6 H, m),

1.49 (3 H, m), 1.53 (18 H, s), 1.61 (18 H, s), 1.92 (12 H, m),

2.58 (30 H, m), 3.08 (6 H, m), 4.02 (12 H, m), 5.06 (6 H, m),

3

6.58 (1 H, d, J_{HH Trans}) 15.7 Hz), 7.28 (2 H, d, J_{HH Trans}

)

15.6 Hz), 7.60 (4 H, s), 7.82 (2 H, s), 8.25 (2 H, s), 10.10 (4 H,

s) ppm. ¹³C NMR (100 MHz, d₆-DMSO) 17.2, 21.5, 22.9, 23.9,

26.6, 27.5, 29.5, 30.1, 31.8, 32.1, 34.7, 41.1, 47.4, 74.2, 111.5,

113.7, 123.3, 136.4, 140.0, 141.0, 165.9, 172.7 ppm. IR ν_max

3446, 1713, 1661, 1618, 1557, 1454 cm^-1. MALDI-TOF MS:

C₈₁H₁₂₂N₆O₁₄, m/z calcd for (M + Na)⁺1425.89, (M + K)⁺

1441.87, found (M + Na)⁺1426.42, (M + K)⁺1442.89. Anal.

Calcd for C₈₁H₁₂₂N₆O₁₄‚2H₂O: C 67.57, H 8.82, N 5.84.

Found: C 67.54, H 8.81, N 5.94. GPC (THF): M_w1812, M_n

1740, M_w/M_n1.04.

Synthesis of 21. To a solution of TREN (0.02 mL, 0.15

mmol) and M₂-[G-1]-CO₂H 11 (0.33 g, 0.48 mmol), in dry CH₃-

CN (7 mL) was added BOP (0.19 g, 0.50 mmol) followed by

triethylamine (0.14 mL, 0.96 mmol), then the mixture was left

stirring at room temperature for 4 days, and the conversion

of the starting material was monitored by TLC (CHCl₃-EtOH

9:1, R_f0.68) and MALDI-TOF MS. The reaction was quenched

by addition of water (10 mL), and the product was extracted

3

6.60 (3 H, d, J_{HH Trans}) 15.8 Hz), 7.31 (3 H, d, J_{HH Trans}

)

15.4 Hz), 7.54 (6 H, s), 7.81 (3 H, s), 8.25 (6 H, m), 10.07 (3 H,

m) ppm. ¹³C NMR (62.8 MHz, d₆-DMSO) δ 17.06, 19.4, 25.2,

25.8, 29.1, 34.3, 35.2, 36.8, 42.2, 62.4, 111.0, 113.1, 124.8, 130.9,

135.7, 138.0, 140.3, 165.2, 170.4, 172.7 ppm. IR ν_max3337, 3092,

1733, 1713, 1639, 1601, 1556, 1452 cm^-1. MALDI-TOF MS:

J. Org. Chem, Vol. 70, No. 1, 2005 77

Aulenta et al.

1

C

₁₁₇H₁₇₄N₁₀O₂₁, m/z calcd for M⁺2055.29, (M + Na)⁺2078.28,

pale brown amorphous solid (76.00 mg, 29% yield). H NMR

(M + K)⁺2094.25, found M⁺2055.90, (M + Na)⁺2077.90, (M

+ K)⁺2095.30. Anal. Calcd for C₁₁₇H₁₇₄N₁₀O₂₁‚7H₂O: C 64.38,

H 8.68, N 6.42. Found: C 64.27, H 8.57, N 5.92. GPC (THF):

M_w1944, M_n1884, M_w/M_n1.03.

(250 MHz, d₆-DMSO) δ 0.68 (24 H, d, ³J_HH) 6.8 Hz), 0.80 (24

3

H, d, J_HH) 6.8 Hz), 0.83 (8 H, m), 0.91 (24 H, d, J_HH) 6.8

Hz), 0.97 (8 H, m), 1.05 (8 H, m), 1.31 (10 H, m), 1.43 (16 H,

m), 1.61 (16 H, m), 1.87 (16 H, m), 2.54 (32 H, m), 3.17 (4 H,

m), 4.61 (8 H, m), 6.61 (2 H, d, ³J_{HH Trans}) 15.5 Hz), 6.85 (4 H,

d, ³J_{HH Trans}) 15.5 Hz), 7.29 (2 H, d, ³J_{HH Trans}) 15.7 Hz), 7.48

Synthesis of 24. To a solution of 1,7-diaminoheptane (0.04

g, 0.05 mmol), C₄-[G-2]-CO₂H 14 (0.20 g, 0.14 mmol), HOAt

(0.03 g, 0.20 mmol), and DiPEA (0.04 mL, 0.22 mmol) in dry

CH₃CN (10 mL) and dry DMF (2 mL) was added HATU (0.09

g, 0.20 mmol), and the reaction was left stirring at room

temperature for 24 h. The reaction profile was monitored by

TLC analysis (CHCl₃-EtOAc 9:1, R_f0.30) and MALDI-TOF

MS. The reaction was quenched by the addition of water (10

mL) and the product was extracted with CHCl₃(3 × 10 mL).

The organic layers were dried (MgSO₄) and filtered and the

solvent was removed under reduced pressure to leave the crude

product. Purification was carried out by column chromatog-

raphy utilizing a gradient elution (from CH₂Cl₂-EtOAc 80:20

to EtOAc-EtOH 95:5), to afford the desired product as a pale

3

(4 H, J_{HH Trans}) 15.4 Hz), 7.69 (8 H, s), 7.75 (4 H, s), 7.78 (4

H, s), 8.02 (2 H, s), 8.31 (2 H, s), 10.14 (8 H, s), 10.49 (4 H, s)

ppm. ¹³C NMR (100 MHz, d₆-DMSO) δ 15.8, 20.0, 21.4, 22.4,

25.1, 28.0, 28.6, 29.9, 30.3, 30.6, 33.2, 45.9, 72.8, 110.4, 112.4,

121.8, 122.0, 123.0, 124.4, 134.6, 135.1, 137.9, 139.6, 140.0,

163.1, 164.1, 169.6, 171.2 ppm. IR ν_max3310, 3099, 1729, 1708,

1669, 1615, 1557, 1453 cm^-1. MALDI-TOF MS: C₈₃H₁₁₄N₆O₁₆,

m/z calcd for (M + Na)⁺3018.77, (M + K)⁺3034.75, found (M

+ Na)⁺3018.36, (M + K)⁺3033.26. GPC (THF): M_w3967, M_n

3510, M_w/M_n1.13.

Acknowledgment. F.A. would like to thank Uni-

lever Research and Development for a postgraduate

studentship. The authors would like to acknowledge

EPSRC (GR/M91884) and SAI Ltd for the funding

provided for the MALDI-TOF MS facilities at the

University of Reading. The authors would also like to

thank EPSRC (GR/R06441) and Polymer Laboratories

Ltd for the funding provided for the gel permeation

facilities at the University of Reading. W.H. would like

to thank EPSRC (GR/M42824) for providing funds for

the HPLC equipment used in this study. In addition,

the authors would like to acknowledge the useful

technical comments and assistance of Professor A.

Gilbert, Dr A. T. Russell, Mr. P. Heath, Miss. A.-L.

Faure, and Dr. S. Maechling during the course of this

study.

brown solid (30.00 mg, 20% yield, mp (broad) 200-230 °C).

¹H NMR (400 MHz, d₆-DMSO, 40 °C) δ 0.84 (24 H, d, J_HH

)

3

6.6 Hz), 1.10 (8 H, m), 1.13 (8 H, m), 1.26 (8 H, m), 1.31 (10 H,

m), 1.40 (8 H, m), 1.53 (24 H, s), 1.57 (8 H, m), 1.67 (24 H, s),

1.88 (4 H, m), 2.63 (32 H, m), 3.17 (4 H, m), 4.05 (16 H, m),

3

5.06 (8 H, m), 6.54 (2 H, d, J_{HH Trans}) 15.6 Hz), 6.86 (4 H, d,

³J_{HH Trans}) 15.6 Hz), 7.29 (2 H, d, ³J_{HH Trans}) 15.3 Hz), 7.41 (4

3

H, d, J_{HH Trans}) 15.4 Hz), 7.68 (8 H, s), 7.75 (4 H, s), 7.80 (4

H, s), 8.02 (2 H, s), 10.17 (8 H, s), 10.50 (4 H, s) ppm. ¹³C NMR

(100 MHz, d₆-DMSO) δ 26.8, 28.5, 34.2, 34.7, 35.8, 37.8, 38.2,

38.4, 40.4, 43.7, 44.3, 71.6, 120.6, 122.5, 131.8, 133.9, 134.2,

139.0, 144.6, 145.0, 148.5, 149.8, 173.0, 175.0, 179.4, 181.6

ppm. IR ν_max3425, 1722, 1666, 1617, 1555, 1453 cm^-1. MALDI-

TOF MS: C₈₃H₁₁₄N₆O₁₆, m/z calcd for (M + Na)⁺3018.77, (M

+ K)⁺3034.75, found (M + Na)⁺3017.90, (M + K)⁺3034.87.

GPC (THF): M_w3054, M_n2770, M_w/M_n1.10.

Synthesis of 25. To a solution of 1,7-diaminoheptane (1.37

mg, 0.087 mmol), M₄-[G-2]-CO₂H 15 (0.35 g, 0.245 mmol),

HOAt (0.041 g, 0.30 mmol), and DiPEA (0.07 mL, 0.40 mmol)

in dry CH₃CN (15 mL) and dry DMF (2 mL) was added HATU

(0.137 g, 0.30 mmol), and the reaction was left stirring at room

temperature for 24 h. The reaction profile was monitored by

TLC analysis (CHCl₃-EtOH 9:1, R_f0.82). The reaction was

quenched by the addition of water (10 mL) and the product

was extracted with CHCl₃(3 × 10 mL). The organic layers

were dried (MgSO₄) and filtered and the solvent was evapo-

rated under reduced pressure to leave the crude product as

Supporting Information Available: General methods

used, DSC data for compounds 8, 10, 12, 14, 13, 15, 16, 20,

21, 22, 23, and 24 (Figures 1s-6s), ¹H NMR spectroscopic data

for 12, 16, 17, 18, 19, 20, 22, and 23 (Figures 7s-15s), MALDI-

TOF mass spectrometric data for 17, 19, 20, and 21 (Figure

16s), and X-ray crystallographic files for 2 and 5 in CIF format.

This material is available free of charge via the Internet at

http://pubs.acs.org.

JO048799A

78 J. Org. Chem., Vol. 70, No. 1, 2005

Article Doi

Synthesis and characterization of fluorescent poly(aromatic amide) dendrimers

DOI: 10.1021/jo048799a

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Article abstract of DOI:10.1021/jo048799a

Full text of DOI:10.1021/jo048799a

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