Total solid-phase synthesis of marine cyclodepsipeptide IB-01212.

A suitable combination of synthetic design, orthogonal protecting groups and coupling reagents was used to complete the first known synthesis of the natural marine cyclodepsipeptide IB-01212. The cyclic, symmetric octapeptide contains two of each of the following residues: L-N,N-Me2Leu, L-Ser, L-N-MeLeu and L-N-MePhe. IB-01212 also features two symmetric ester bonds between the hydroxyl group of Ser and the carboxyl function of the N-MePhe. Total solid-phase syntheses of the product was performed in parallel via three distinct routes: dimerization of heterodetic fragments, linear synthesis, and convergent synthesis. The convergent strategy gave the best results in terms of product yield and purity and is particularly suitable for the large-scale synthesis of IB-01212 and similar peptides.