Studies on Amino Acids and Peptides, 9. 5‐Thioxoproline and 5‐Thioxoproline Esters – Synthesis and Crystal Structures

Abstract

Abstract 5‐Thioxoproline ( 2a ) is synthesized from 5‐oxoproline ( 1a ) at room temperature with 2,4‐bis(4‐methoxyphenyl)‐1,3,2,4‐dithiadiphosphetane 2,4‐disulfide ( 3 ) in DME. The carboxy group requires no protection because of the mild reaction conditions. 5‐Thioxoproline esters are synthesized either by thionation of the corresponding 5‐oxoproline esters with 3 or by esterification of 2a . Compounds 2a and 5‐thioxoproline methyl ester ( 2b ) both crystallize in the space group P 2 1 2 1 2 1 with Z = 8. Bond lengths and angles in the compounds are compared, and the small differences explained by differences in hydrogen bond pattern.