Structure of cyclo-(L-threonyl-D-valyl-L-prolyl-sarcosyl-N-methyl-L-valyl-OThr) at 153 K

The crystal structure of cyclo-(L-Thr-D-Val-L-Pro-Sar-N-L-MeVal-O Thr ), C 23 H 39 N 5 O 6 .HCl.MeOH.H 2 O is reported. This cyclic pentapeptide lactone represents one of the two peptide units of actinomycin and is a 16-membered depsipeptide. The backbone adopts a flat conformation similiar to that found for an analogous N-protected pentapeptide lactone by Mauger, Stuart, Ferretti & Silverton [J.Am. Chem. Soc. (1985), 107, 7154-7163]