s u2014 n boc 4 10 b boronophenylalanine which was then washed twice with water and dried in a vacuum oven at 50 u00b0 c for a minimum of 4 hours to an lod of less than 0 5 to afford 25 8 g of s u2014 n boc 4 10 b boronophenylalanine as white solid which was 99 6 pure determined by hplc the yield was 65 1 the melting point specific rotation 1 h nmr data 13 c nmr data ir data and ms data of the obtained s u2014 n boc 4 10 b boronophenylalanine are as follows 1 h nmr 500 mhz dmso d 6 u03b4 8 0 s 2h 7 7 d j 7 7 hz 2h 7 2 d j 7 6 hz 2h 7 0 d j 8 4 hz 2h 4 1 m 1h 3 0 dd j 13 8 4 5 hz 1h 2 8 dd j 13 7 10 3 hz 1h 1 3 s 9h 13 c nmr 125 mhz dmso d 6 u03b4 173 63 155 48 139 96 134 06 131 94 128 18 78 13 55 06 36 53 28 19 ir kbr u03bd max 3331 2979 1717 1689 1537 1399 1372 1365 1285 1165 1045 cm u2212 1 and hrms esi calculated for c 14 h 20 10 bno 6 m u2212 h u2212 307 1420 found 307 1333 preparation of 4 10 b borono l phenylalanine l 10 b bpa from s u2014 n boc 4 10 b boronophenylalanine a suspension of s u2014 n boc 4 10 b boronophenylalanine 20.