Synthese eines cyclischen Depsipeptides mittels Amidcyclisierung

Synthesis of a Cyclic Depsipeptide via an Amide Cyclization The synthesis of ( S )‐Pms‐( R )‐Pro‐( S )‐Ala‐Aib‐N(CH 3 ) 2 ( 12 ) has been achieved according to Scheme 3 . For the formation of fragment 11 , the reaction of Z‐alanine (Z = benzyloxycarbonyl) and 3‐dimethylamino‐2,2‐dimethyl‐2‐azirine ( 1 ) has been used, whereby 1 serves as an aminoisobutyric‐acid dimethylamide (aib‐N(CH 3 ) 2 ) equivalent. Treatment of a suspension of 12 in toluene with HCl gas at 100° led to the cyclic depsipeptide 13 in 72% yield ( Scheme 4 ). In presence of water, the acid 14 was isolated as the sole product. A mechanism for the formation of 13 and 14 via an oxazolinone intermediate, is postulated in Scheme 4 .