合成路线1

(i) The formation of a 16-membered depsipeptide: For the first step, L-valine methyl ester (I) was coupled to N-Fmoc-L-threonine using the BOP reagent [(benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate], removing the N-Fmoc group with Et2NH and coupling to N-Fmoc-(S-triphenylmethyl)-D-cysteine to yield the tripeptide (II). The tetrapeptide (III) was prepared by deprotection of the tripeptide (II) and BOP-mediated peptide coupling of the resulting amine with N-Fmoc-D-valine. The secondary hydroxyl group was activated as the tosylate and eliminated by treatment with DABCO to produce the internal alkene. After removal of the Fmoc protecting group by addition of Et2NH to the reaction mixture, the 16-membered depsipeptide (IV) was formed.