Patent ID: 8283456

Claim:
A method comprising the steps of: (a) providing a mixture of prosapogenins of formula IV-a: wherein: is a single or double bond; Y′ is hydrogen, halogen, alkyl, aryl, OR, OR y , OH, NR 2 , NHR, NH 2 , SR, or NROR; W is Me, —CHO, —CH 2 OR x , or —C(O)R y ; V is hydrogen or —OR x ; R y is —OH, or a carboxyl protecting group, wherein the carboxyl protecting group, when taken with its attached carbonyl group, is an ester, amide, or hydrazide; R s1 is each occurrence of R x′ is independently an optionally substituted group selected from 6-10-membered aryl, C 1-6 aliphatic, or C 1-6 heteroaliphatic having 1-2 heteroatoms independently selected from the group consisting of nitrogen, oxygen, and sulfur; or: two R x′ are taken together to form a 5-7-membered heterocyclic ring having 1-2 heteroatoms independently selected from the group consisting of nitrogen, oxygen, and sulfur; each occurrence of R is independently hydrogen, an optionally substituted group selected from acyl, arylalkyl, 6-10-membered aryl, C 1-12 aliphatic, or C 1-12 heteroaliphatic having 1-2 heteroatoms independently selected from the group consisting of nitrogen, oxygen, and sulfur; or: two R on the same nitrogen atom are taken with the nitrogen to form a 4-7-membered heterocyclic ring having 1-2 heteroatoms independently selected from the group consisting of nitrogen, oxygen, and sulfur; and each occurrence of R x is independently hydrogen or an oxygen protecting group selected from the group consisting of alkyl ethers, benzyl ethers, silyl ethers, acetals, ketals, esters, and carbonates; (b) treating said mixture of prosapogenins of formula IV-a under suitable conditions to form a mixture of prosapogenins of formula IV: wherein each of , R y ′ Y′, V, and W is as defined for compounds of formula IV-a, and each occurrence of R x is independently hydrogen or an oxygen protecting group selected from the group consisting of alkyl ethers, benzyl ethers, silyl ethers, acetals, ketals, esters, and carbonates; R s is with the proviso that at least one R x group is not hydrogen; and (c) obtaining a prosapogenin of formula IV by suitable physical means.