D. Seebach, G. Herrmann, U. Lengweiler
Dec 1, 1996
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0
Influential Citations
64
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Journal
Angewandte Chemie
Abstract
Dendrimers are attracting growing interest for use in stereoselective synthesis,['] as a new type of material,[21 and in biological studies, for example as DNA carriers.[31 We now report on the first synthesis of monodisperse, enzymatically degradable, polyanionic dendrimers from (R)-3hydroxybutanoic acid (HB)[41 and trimesic acid. The convergent synthesis starts with the previously described14] benzyl esters la and lb of the dimer and the tetramer of HB, respectively, which were used as elongation units. For the assembly of the dendritic core and the branching units we employed the commercially available trimesic acid trichloride 3 and the TBDPS-protected 5hydroxymethyl1,3-benzenedicarboxylic acid dichloride 4,15] which can be easily obtained from the corresponding trimethyl trimesate. Acylation of the HB-oligomers 1 with 3 gave the core structures 5, and debenzylation yielded the tricarboxylic acids 6. Branching unit 7 was obtained by acylation of 1 with 4. The branches 10 for the dendrimers of the second generation were synthesized starting from the silylated ester 7, followed by debenzylation (+ 8), then activation (+9),['] and subsequent acylation of the desilylated derivative of 7 with the acid chloride 9. The coupling of 6 with the desilylated branches 7 and 10 finally gave the dendrimers of the first (green circle in formula 11/12) and of the second generation (ll), respectively. The selective hydrogenolysis of the terminal benzyl groups of the dendrimers was achieved by catalytic transfer hydrogenation[61 and gave the polyanionic dendrimers of the first and second generation (12a). The dendritic compounds were obtained in 150 mg (llb) to 450 mg (lla) quantities as viscous oils that were soluble in CH,Cl,. All compounds were fully characterized (optical rotation, IR, 'H and I3C N M R spectroscopy, MS, elemental analysis; see experimental part a); Figure 1 shows five MALDI-MS molecular peaks and proves the identity and the monodispersity of the corresponding compounds. 0 la , l b (R = Bn) 2a, 2b (R = H) 3