SYNTHESIS OF BIOMARKERS IN FOSSIL-FUELS - C-23 AND C-24 DIASTEREOMERSOF ETHYL-18,19-DINORCHOLESTA-1,3,5,7,9,11,13-HEPTAENE

A synthesis of the C-23 and C-24 diastereomers of triaromatic dinoster oids useful as maturation biomarkers for marine-sourced petroleum was developed. Conversion of stigmasterol to S)-4-methyl-19-norstigmasta-1 ,3,5(10),22-tetraene, ozonolysis of the stigmasterol sidechain, sodium borohydride reduction, and sequential treatment with methanesulfonyl chloride and sodium iodide furnished odomethyl)-4-methyl-19-norpregna- 1,3,5(10)-triene. The alkylation of this iodide with methyl 3,4-dimeth yl-2-pentenoate provided the C-23R and C-23S diastereomers of methyl ( 20R,23 ne-19-norcholesta-1,3,5(10)-triene-23-carboxylate, reduction wi th lithium aluminum hydride, and separation gave (20R,23R)- and xymeth yl)-4-methyl-24-methylene-19-norcholesta-1,3 The further reduction of the 24-methylene and the hydroxymethyl group in 4-methyl-24-methyl-19- norcholesta-1,3,5(10)-triene provided (20R,23R,24R)- and 4,23,24-trime thyl-19-norcholesta-1,3,5(10)-triene. In the same fashion, the reducti on of the 24-methylene and the hydroxymethyl group in ymethyl)-4-methy l-24-methylene-19-norcholesta-1,3, 5(10)-triene provided (20R,23S,24R) - and ,23,24-trimethyl-19-norcholesta-1,3,5-(10)-triene. A chloranil o xidation of each of these monoaromatic diastereomers to (20R)-4,17 hyl -18,19-dinorcholesta-1,3,5,7,9,11,13,15-octaene and a catalytic hydrog enation furnished the C-23 and C-24 diastereomers of the triaromatic b iomarker, (20R)-4,17 thyl-18,19-dinorcholesta-1,3,5,7,9,11,13-heptaene .