Steroids of the spirostan and furostan series from plants of the genus Allium. XXVII. Alliosterol and allosides A and B from Allium suvorovii and Allium stipitatum ? Structural analogs of furostanols

Open-chain steroidal glycosides, a diverse class of plant saponins

“…The alliosterol skeleton (29) was reported in 1991 as the aglycone of allosides A (30) and B (31) isolated from Allium suworowii Regel and Allium stipitatum Regel, from which the trivial name of this aglycone is derived. 27 Alliosterol glycosides may conceptually be derived via 1b-hydroxylation of saponins possessing the above discussed (22S)-3b,16b,22-trihydroxycholest-5-ene aglycone (11), which co-occur in plants of the Allium genus. 16 Both 30 and 31 possess a single b-D-galactopyranosyl residue linked at position C-16, while the bisdesmosidic 31 also has a b-D-glucopyranosyl unit attached at C-1.…”

“…Typically, the absolute congurations of positions within the sidechain are assigned either by comparison of their 1 H and 13 C NMR chemical shis with those of closely related structures, or by degradation into known structural elements. One of the most reliable methods for determination of sidechain stereochemistry is X-ray crystallographic analysis, either of the naturally occurring glycoside 110 or aglycone, 27,51,104 or in combination with total synthesis. 118 The modied (or advanced) Mosher ester analysis has also been used to determine the absolute conguration of C-22 in some glycosides of the alliosterol family, 16,36,45,102,107 although this method suffers from problems of selectivity if more than one secondary alcohol is present in the aglycone.…”