Synthesis and Properties of Monodisperse Chiral Dendrimers (up to Fourth Generation) with doubly branched building blocks: An intriguing solvent effect

Abstract

'Fully chiral' dendrimers, containing a stereogenic center at each and every branching point, have been prepared using a chiral core triol with aromatic elongating units (cf 27) and chirdl branch diols (cf. 8, 12. and 24) as building blocks. The biggest dendrimer prepared is of the 4th generation (33: 46 building blocks, 93 stereogenic centers, lo2' possible stereoisomers), and has been obtained by a convergent growth approach in 32 steps starting from the biopolymer poly[(R)-3-hydroxybutanoic acid] (P(3-HB)). All compounds were shown to be monodisperse by MALDI-TOF mass spectrometry. Spin-lattice relaxation-time (TI) measurements and size-exclusion chromatography show typical features of structurally related achiral dendrimers. The influence of the chirdl building blocks on the shape of the whole dendrimer has been investigated by chiroptical measurements: the specific rotation can be considered as average of all chiroptical properties of its constituent chiral units, independent of the solvent, the concentration, and the temperature. On the other hand, regularity in the circular dichroism (CD) spectra is completely lost with variation of the solvent (cf. Fig. 13).1. Introduction. -Chirality, a characteristic property of biological systems, plays an important role in several highly selective recognition processes and reactions [3] [4]. Furthermore, in a biomacromolecule the 'chirality' of the monomer is often 'amplified', and a chiral superstructure, e.g., a helix is formed [5]. Similar observations have been made with synthetic polymers [6-81 or lipid aggregates [9-111. Because of their well-defined molecular weight and structure, one can expect that chiral dendrimers3) could be useful as model compounds for studying how 'chirality is expressed' in a macromolecular system. It can be anticipated that introducing chiral branching units into the dendrimer should result in a non-symmetrical, non-spherical overall shape and should provide chiral cavities. These structures might also be useful for asymmetric catalysis, chiral recognition, and resolution processes.In our preceding paper on 'fully chiral' dendrimers with triple branching units, we reported on a diastereoselective effect in the reactions used for coupling dendrons with cores [14]. All chiral building blocks, e.g., core triol 2 [15-171 and branch triol 3 [1][14][18], were prepared from the dioxanone 1 [19][20], which is easily accessible from the biopolymer P(3-HB)4) by aldol addition and reduction.

Metal‐Induced Chiral Folding of Depsipeptide Dendrimers

“…For the Cu secondary interactions in chiral dendrimers, [24][25][26][27] conformational order was found to be lacking. [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] Recently, we introduced the concept of chiral depsipeptide dendrimers as peptide or protein mimetics. [34,43] This new class of dendrimers closely resembles the structures of natural depsipeptides, which consist of a-hydroxy and a-amino acids connected by ester and amide linkages.…”

Preparation of Polystyrene Beads with Dendritically Embedded TADDOL and Use in EnantioselectiveLewis Acid Catalysis

“…of Et 2 Zn[32] were prepared according to reported procedures. The compounds 1 [1][24], 2 ± 4[22], 11[39], 15[31], and 28[20a] were synthesized according to literature procedures. PhCHO was distilled prior to use.…”

Chiral dendrimers—from architecturally interesting hyperbranched macromolecules to functional materials

“…Considering that steric factors prevented the preparation of higher generation dendrimers featuring triple branched building blocks, the synthesis fully chiral dendrimers with double branched building blocks was carried out. 95 Consequently dendrons up to the 5th and dendrimers up to the 4th generations were prepared. In these systems diastereoselectivity was not observed and the specific rotation values closely resembled the predicted values.…”