DIASTEREOSELECTIVE SYNTHESIS OF ALLIIN BY AN ASYMMETRIC SULFUR OXIDATION

L-(+)-Alliin (7) has been synthesized from S-allyl-L-cysteine (3) by a n asymmetric sulfur oxidation using tetraisopropyl-ortha-titanate [Ti( O-iPr)(4)] in equimolar amounts. Chirality of the resulting sulfoxide was guided by either (+)- or (-)diethyl tartrate as chiral auxiliary w hich led to the (-)- or (+)-isomer of L-alliin (7, 8), respectively. T o allow this type of oxidation, the amino acid functions of 3 were pro tected by a tert.-butoxycarbonyl- and a 9-fluoronylmethyl group. Alter natively, an enzyme catalysed asymmetric sulfur oxidation by cyclohexa none oxygenase was carried out. The products were investigated by IR, MS and NMR spectroscopy. The ratio between the diastereomers 7 and 8 w as determined by HPLC. Also IR spectroscopy allowed an estimation of t he approximate ratio 7/8.