Studies on the synthesis and structure of new urea-linked sugar podando-coronand derivatives

With the aim to develop direct, simple, and efficient coupling procedures i nvolving saccharides and cyclodextrins (CDs),the modified Staudinger method . the phosphine imide method, was chosen as a promising versatile way to re ach the goals. Thus, the new cyclam derivatives 6-9 were obtained in good y ields (ser Scheme). In the case of beta -cyclodextrin, the method also allo wed the synthesis of the icosa-O-acetyl-6(A)-isocyanato-6(A)-deoxy-beta -CD sugar isocyanate 11 and of symmetrical or unsymmetrical carbohydrate carbo diimides 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 u rea functions in the conformational equilibrium of the molecules.