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Efficient Asymmetric Synthesis of (S)- and (R)-N-Fmoc-S-Trityl-α-methylcysteine Using Camphorsultam as a Chiral Auxiliary

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journal contribution
posted on 25.06.2004, 00:00 by Satendra Singh, Samala J. Rao, Michael W. Pennington
(1R)-(+)-2,10- and (1S)-(−)-2,10-camphorsultam were acylated with ethyl 2-phenylthiazoline 4-carboxylate to afford (+)- and (−)-2-phenylthiazolinylcamphorsultam, which were stereoselectively alkylated with MeI in the presence of n-BuLi. Alkylation of these phenylthiazolinylcamphorsultams occurred from the β-face rather than α-face, resulting in the formation of (S)-α-methylcysteine from (1R)-(+)-2,10-camphorsultam and (R)-α-methylcysteine from (1S)-(−)-2,10-camphorsultam after acidic hydrolysis. Subsequent protection of the side chain thiol group with trityl alcohol and α-amine function with Fmoc-OSu furnished fully protected (S)- and (R)-N-Fmoc-S-trityl-α-methylcysteine in overall 20% yield.