Xue-Bin Shao

Hydrogen bonding-mediated oligobenzamide foldamer receptors that efficiently bind a triol and saccharides in chloroform

The self-assembly of two novel intramolecular hydrogen bonding-driven foldamers is described. Two linear symmetric aromatic amide oligomers, 1 and 2, which are incorporated with benzene subunits, have been prepared by continuous amide-coupling reactions. The existence of three-centred hydrogen bonds in the oligomers and consequently the folding conformation of the oligomers in solution have been characterized by 1H NMR experiments and by comparing them with the reported solid state structure of the identical structural skeleton. Molecular modeling reveals a rigid crescent conformation for 1 with a cavity of ca. 0.9 nm in diameter and a helical conformation for 2 with a cavity of ca. 0.8 nm in diameter. Due to the existence of intramolecular hydrogen bonding, all the CO groups in both oligomers are located inwardly. The binding of 1 and 2 towards a trihydroxyl guest and four saccharide derivatives have been investigated with 1H NMR, fluorescence, and circular dichroism spectroscopy. The association constants of the corresponding 1 ∶ 1 complexes have been determined by fluorescence titration experiments.

A general approach to l-tyrosine porphyrins

Abstract A novel and general approach has been developed to prepare l -tyrosine-containing porphyrins. The key intermediates, 2- tert -butoxycarbonylamino-3-(3-formyl-4-hexyloxy-phenyl)-propionic acid hexyl ester and 2- tert -butoxycarbonylamino-3-(3-formyl-4-methoxy-phenyl)-propionic acid methyl ester, were prepared by the Reimer–Tiemann reaction of Boc-protected l -tyrosine, which was followed by esterification and alkylation of the phenol hydroxide. A number of novel chiral l -tyrosine porphyrins were obtained from the reactions of 2- tert -butoxycarbonylamino-3-(3-formyl-4-alkoxy-phenyl)-propionic acid ester with different dipyrrolylmethanes and the reaction of 5-(4-trifluoromethylphenyl)pyrromethane afforded the highest yield. The tyrosine porphyrins could be readily deprotected to afford the corresponding diacid or diamine derivatives.