Total synthesis of a series of thiazolinone and thiazolidinone analogues of the antibacterial oxazolinone antibiotic indolmycin is described. The synthetic route involves nucleophilic displacement of mesyloxy and chloro groups from methyl 2-substituted-3-(indol-3-yl)propionates 3 and 4 and butyrate 19 with N-substituted thioureas. The formation of the rearranged chloro esters 29, 43, and 44 from beta(RS,RS)-methyl indolmycenate (27), alpha(RS,SR)-methyl 2-hydroxy-3-(2-methylindol-3-yl)butyrate (39), and alpha-methyl 2-hydroxy-3-(indol-3-yl)valerate (41) supports a reaction mechanism involving neighboring group participation by the indole C-3 carbon during nucleophilic displacement on the beta-carbon of a C-3 substituent. Structure-activity relationships are discussed. Although neither indolmycin nor its diastereoisomer isoindolmycin is antiviral, 2-monoalkylaminothiazolinone analogues have in vitro activity against both RNA viruses and bacteria. The most active compound is the sulfur isostere of indolmycin, and only the levorotatory enantiomer 46, with the same absolute stereochemistry as natural indolmycin, has antimicrobial activity.