Biologically active glycosides from asteroidea, XXI. Structure of pectinioside C: Determination of the stereochemistry of the C‐17 side chain of the steroidal aglycone

Abstract The 3,6‐di‐O‐acetyl derivative 3 of the desulfated aglycone of pectinioside C, (20S,24S)‐24‐ethylthoransterol A (2), and its 24R and 24RS stereoisomers 4 and 27 have been synthesized stereoselectively from the pregnane derivative 3,6‐di‐O‐acetyl‐asterone (5). Herewith, the stereochemistry at the C‐17 side chain of 2 and of pectinioside C (1) has been determined. (20S,24S)‐3β‐Acetoxy‐24‐ethyl‐20‐hydroxycholest‐5‐en‐23‐one (18), its 24R and 24RS stereoisomers 21 and 24, respectively, and some steroids with (20S)‐20‐hydroxy‐24ζ‐methyl‐26‐homo‐25ζ‐cholestane side chain have also been synthesized.