Enantioselective synthesis of Fmoc-l-3-(2-benzothienyl)alanine (2-BtAla) via diastereoselective alkylation of a glycine equivalent |
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Authors: | Satendra S. Chauhan Suisheng Shang Michael W. Pennington |
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Affiliation: | Peptides International Inc, 11621 Electron Drive, Louisville, KY 40299, USA |
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Abstract: | Stereoselective alkylation of the anion derived from (2R)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine with 2-chloromethylbenzothiophene afforded the corresponding trans-monosubstituted product, (2S,5R)-2-((1-benzo[b]thiophen-2-yl)methyl)-3,6-dimethoxy-5-(propan-2-yl)-2,5-dihyropyrazine in 88% yield. Hydrolysis of the alkylated product using 40% TFA/H2O at 0?°C and subsequent protection of the α-amino functional group with Fmoc-OSu afforded Fmoc-l-3-(2-benzothienyl)alanine methyl ester in 88% yield. Hydrolysis of the methyl ester with aqueous LiOH gave Fmoc-l-3-(2-benzothienyl)alanine in 62% overall yield. |
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Keywords: | 2-BtAla Diastereoselective alkylation Enantioselective synthesis Heteroaromatic amino acid |
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