.beta. -D-Xylopyranoside, (3.beta. ,4.beta. ,5.alpha.,6.alpha.,15.beta. ,16.beta. ,24R)-3,4,8,15,16-pentahydroxy-6-(sulfooxy)stigmastan-29-yl 4-O-methyl- AIDS-168492 AIDS168492 Certonardoside I