Synthesis of 4,6-Difluoro-Tryptophan as a Probe for Protein 19F NMR

A scalable procedure for the synthesis of 4,6-difluorotryptophan is reported based on a deaminative coupling of a 4,6-difluorogramine with 2-benzylthio-1,5-dihydro-4H-imidazolone as glycine equivalent. Thus prepared 4,6-difluorotryptophan was incorporated into the C-terminal domain of the HIV-1 capsid protein (CA-CTD), and 19F spectra of the 4,6-difluoro Trp CA CTD were recorded and compared to the singly fluorinated counterparts.We thank the Basque Government (EJ, grant IT1583-22) and Agencia Estatal de Investigación (grants PID2019-109633GB-C21/AEI/10.13039/501100011033 and PID2022-137153NB-C21/AEI/10.13039/501100011033) for financial support. The authors are grateful for the technical and human support provided by SGIker (UPV/EHU/ERDF, EU). I.H. thanks EJ for a fellowship. R.M-P. was supported by the Health Sciences Diversity Scholars Program at the University of Pittsburgh and F.B. by a post-doctoral fellowship from the American Heart Association. The work in the Gronenborn laboratory was supported by NIH grant U54AI170791