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Synthesis 2010(10): 1673-1677  
DOI: 10.1055/s-0029-1218707
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

N-Benzyl-Protection of Amino Acid Derivatives by Reductive Alkylation with α-Picoline-Borane

Yasushi Kawasea, Takehiro Yamagishia, Teruo Kutsumaa, Tadashi Kataokab, Kimio Uedac, Takeo Iwakumac, Tadashi Nakatad, Tsutomu Yokomatsu*a
a School of Pharmacy, Tokyo University of Pharmacy & Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
Fax: +81(42)6763239; e-Mail: yokomatu@toyaku.ac.jp;
b Yokohama College of Pharmacy, 601 Matano-cho, Totsuka-ku, Yokohama, Kanagawa 245-0066, Japan
c Development Laboratory, Junsei Chemical Co., LTD, 1-6 Ohmano-cho, Koshigaya, Saitama 343-0844, Japan
d Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
Further Information

Publication History

Received 19 January 2010
Publication Date:
24 March 2010 (online)

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Abstract

A convenient method for N-protection of amino acid derivatives with a benzyl group by reductive alkylation of amino acid derivatives with α-picoline-borane is described. Amino acid esters or amino alcohols were treated with aryl aldehydes in methanol/acetic­ acid in the presence of α-picoline-borane to give N-benzyl-protected amino acid derivatives in good yields.

Key words

amino acid esters - amino alcohols - benzylation - protecting groups - reductions

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9

Thermal stabilities of α- and γ-picoline-borane were examined. They were non-explosive at 100 ˚C and did not decompose under ambient conditions over two years judging from the HPLC analysis of the products.