Antiviral stereoisomers of 3,5-bis（2-hydroxybut-3-en-1-yl）-1,2, 4-thiadiazole from the roots of Isatis indigotica

Four stereoisomers of 3,5-bis（2-hydroxybut-3-en-1-yl）-l,2,4-thiadiazole, named insatindigothiadia- zoles A-D （1a-1d）, were isolated from the roots oflsatis indigotica. Their structures were determined by spectroscopic analysis; specifically, the absolute configurations were assigned by using the MPA determination rule based on △δrs values of MPA esters, and supported by electronic CD （ECD） calculations. Proposed biosynthetic pathways and preliminary investigations of the biological activities of la-1d against influenza virus A （H3N2）, Coxsackie virus B3, and/or HSV-1 are also discussed.