L-Phenylalanine-1-13C, N-t-Boc derivative, N-(tert-Butoxycarbonyl)-L-phenylalanine-1-13C Boc-13C-Phe-OH L-Phenylalanine, N-t-Boc derivative-(carbonyl-13C) N-(tert-Butoxy(carbonyl-13C)-L-phenylalanine L-Phenylalanine-1-13C, N-t-Boc derivative N-(TERT-BUTOXYCARBONYL)-L-PHENYLALANINE-CARBOXY-13C N-(tert-butoxycarbonyl)-L-phenylalanine-carboxy-1 N-(TERT-BUTOXYCARBONYL-CARBONYL-13C)-L-P HENYLALANINE, 99 ATOM % 13C