STARFISH SAPONINS .53. A REINVESTIGATION OF THE POLAR STEROIDS FROM THE STARFISH OREASTER-RETICULATUS - ISOLATION OF 16 STEROIDAL OLIGOGLYCOSIDES AND 6 POLYHYDROXYSTEROIDS

A reinvestigation of the starfish Oreaster reticulatus has led to the isolation of sixteen steroidal oligoglycosides and six polyhydroxyster oids. One steroidal monoglycoside has been identified as asterosaponin -1 [5], previously isolated from the same organism, and one pentaglyco side steroidal sulfate has been identified with the known ophidianosid e F [1], previously isolated from starfish species of the family Ophid iasteridae. The novel pentaglycoside steroidal sulfates reticulatoside s A [3] and B [4] represent the second examples of asterosaponins cont aining the 5 alpha-cholesta-9(11)-en-3 beta,6 alpha,20,22-tetraol agly cone. Of the remaining new steroidal oligoglycosides, the majority are characterized by the common (24S)-5 alpha-cholesta-3 beta,6 alpha,8,1 5 alpha,24-pentaol aglycone, with some having a sulfate group at C-6, and differing in the sugar moiety. Compounds 11, 12, 15,and 16 represe nt major departures from the more common structural features encounter ed in steroidal glycosides from starfish with the presence in 11 and 1 2 of a rare 5-O-methylgalactofuranosyl unit and in 15 and 16 of a 3-O- methyl-2-O-sulfate-xylopyranosyl unit. The latter was shown by nmr dat a combined with molecular dynamics calculations to exist: in an 8:2 eq uilibrium mixture of the C-1(4) and C-4(1) conformations.