An efficient synthesis of N-tert-butoxycarbonyl-O-cyclohexyl-L-tyrosine

A facile and efficient synthesis of N-tert-butoxycarbonyl-O-cyclohexyl-L-ty rosine [Boc-Tyr(Chx)-OH] is described. Boc-Tyr-OH was treated with NaH in d imethylformamide and then with 3-bromocyclohexene to give N-Boc-O-(cyclohex -2-enyl)-L-tyrosine [Boc-Tyr(Che)-OH] in 70% yield. Hydrogenation of Boc-Ty r(Che)-OH over PtO2 afforded Boc-Tyr(Chx)-OH in almost quantitative yield. The highest yield was achieved when a side product in the synthesis of Boc- Tyr-OH, Boc-Tyr(Boc)-OH, was not removed, because it was also converted to Boc-Tyr(Che)-OH without any additional manipulations. The new synthetic met hod described here is convenient for practical use, and would facilitate th e widespread use of the Chx group for the hydroxy-protection of Tyr.