Synthesis of carbosilane dendritic wedges and their use for the construction of dendritic receptors.

A divergent route for the synthesis of carbosilane wedges that contain either a bromine or amine as focal point has been developed. These new building blocks enable the construction of various core-functionalized carbosilane dendrimers. As a typical example carbosilane dendrimers up to the third generation containing a N,N',N''-1,3,5-benzenetricarboxamide core (G1-G3) have been synthesized. This new class of molecules has been studied as host molecules and they have been found to bind protected amino acids as guest molecules via hydrogen bonding interactions. A decrease in the association constants was observed for the higher generation dendritic hosts, which is attributed to the increased steric hindrance around the core where the binding site is located. The binding properties of the dendritic host molecules can be tuned by modifying the binding motif at the core of the carbosilane dendrimers. A higher association constant for N-CBZ-protected glutamic acid 1-methyl ester (5) was observed when the third generation N,N',N''-1,3,5-tris(L-alaninyl)benzenetricarboxamide core-functionalized carbosilane dendrimer (G3') was used as the host molecule compared to G3. Different association constants for the formation of the diastereomeric G3'.L-5(K=295 M(-1)) and G3'.(D-5)(2) (K=236 M(-1)) host-guest complexes were observed, pointing to a small enantioselective recognition effect. The difference between the association constants for the formation of the G3'.(L-5)(2) and G3'.(D-5)(2) host-guest complexes was much more pronounced, K=37 M(-1)versus K=10 M(-1), respectively.