摘要:
Two external beta-turn templates have been synthesised and one of them has been derivatised as a GLDV-tetrapeptide. In the course of the synthesis an interesting dichotomy was observed in the condensation of exocyclic enamines such as 4 and 19 with protected dehydroamino acids using phosphorus trichloride. When dehydroamido acids were condensed with the enamines 4 and 19 then 6/6 and 6/5 fused bicyclic compounds such as 5 and 20, respectively, were obtained, whereas, when dehydroamino acid urethanes were used, the 5/6 and 5/5 fused products 7 and 23 were obtained. The bicyclic template 20 was converted to the GLDV-tetrapeptide derivative 31 but the sensitivity to base of the acyl-enamine system of the template reduced the yield in the synthesis of the external turn 35. (C) 2004 Elsevier Ltd. All rights reserved.