monofluorinated L-tryptophan 6'-fluoro-L-tryptophan 17.989999771118164062 17.99057769775390625 204.06988525390625 204.1999969482421875 6-fluorotryptophan A protein modification that effectively converts an L-tryptophan residue into an 6'-fluoro-L-tryptophan. C 11 F 1 H 9 N 2 O 1 F 1 H -1 MOD:01481 PSI-MOD W artifact