Efficient asymmetric synthesis of (S)- and (R)-N-Fmoc-S-trityl-alpha-methylcysteine using camphorsultam as a chiral auxiliary |
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Authors: | Singh Satendra Rao Samala J Pennington Michael W |
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Affiliation: | Bachem Bioscience Inc, 3700 Horizon Drive, King of Prussia, Pennsylvania 19406, USA. ssingh@usbachem.com |
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Abstract: | (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 beta-face rather than alpha-face, resulting in the formation of (S)-alpha-methylcysteine from (1R)-(+)-2,10-camphorsultam and (R)-alpha-methylcysteine from (1S)-(-)-2,10-camphorsultam after acidic hydrolysis. Subsequent protection of the side chain thiol group with trityl alcohol and alpha-amine function with Fmoc-OSu furnished fully protected (S)- and (R)-N-Fmoc-S-trityl-alpha-methylcysteine in overall 20% yield. |
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