Total Synthesis of Cryptophycin 3

The depsipeptide cryptophycin 3 ( 5 ) and the cryptophycin analogue 43 were prepared from the corresponding four subunits. The tripeptide analogue 34 was acquired from the starting amino ester 33 , which contains fragments D and C. After extension at the carboxyl function by esterification with the hydroxy ester 10 , the seco compounds 37 and 42 were obtained. Ring closure was achieved by macrolactamization in the presence of TBTU as condensing agent. This work features a streamlined synthesis of the hydroxy ester 10 , a short synthesis of the amino acid 14 by enantioselective alkylation of the glycinimine 21 , and the use of the Fmoc protecting group for the amino functions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)