Studies on the Synthesis and Structure of New Urea-Linked Sugar Podando-Coronand Derivatives

Abstract

With the aim to develop direct, simple, and efficient coupling procedures involving saccharides and cyclodextrins (CDs), the modified Staudinger method, the phosphine imide method, was chosen as a promising versatile way to reach the goals. Thus, the new cyclam derivatives 6 – 9 were obtained in good yields (see Scheme). In the case of β-cyclodextrin, the method also allowed the synthesis of the icosa-O-acetyl-6A-isocyanato-6A-deoxy-β-CD sugar isocyanate 11 and of symmetrical or unsymmetrical carbohydrate carbodiimides 12 and 17 under smooth conditions and in a simple way. Structural, theoretical, and experimental investigations on several urea-like cyclams revealed the fundamental role played by permanent strong H-bonds between urea functions in the conformational equilibrium of the molecules.