Design and syntheses of novel calix[4](aza)crowns: Neutral receptors for alpha-amino acids

A series of novel calix[4](aza)crowns 2a-2d containing acy1hydrazone groups was designed and synthesized via 1 + 1 condensation of calix[4]-1,3-substituted benzaldehyde derivative 1 with bis-hydrazides in 85-90% yields. They showed good complexation abilities toward alpha-amino acids and exhibited complexation selectivity toward tryptophane.