Synthesis of Differentially Protected Azatryptophan Analogs via Pd<sub>2</sub>(dba)<sub>3</sub>/XPhos Catalyzed Negishi Coupling of <i>N</i>-Ts Azaindole Halides with Zinc Derivative from Fmoc-Protected <i>tert</i>-Butyl (<i>R</i>)-2-Amino-3-iodopropanoate
作者:Roshan Y Nimje、Devaiah Vytla、Prakasam Kuppusamy、Rajeswari Velayuthaperumal、Lokesh Babu Jarugu、China Anki Reddy、Nanjundaswamy Kanikahalli Chikkananjaiah、Richard A. Rampulla、Cullen L. Cavallaro、Jianqing Li、Arvind Mathur、Anuradha Gupta、Amrita Roy
DOI:10.1021/acs.joc.0c00973
日期:2020.9.4
Unnatural amino acids play an important role in peptide based drug discovery. Herein, we report a class of differentially protected azatryptophan derivatives synthesized from N-tosyl-3-haloazaindoles 1 and Fmoc-protected tert-butyl iodoalanine 2 via a Negishi coupling. Through ligand screening, Pd-2(dba)(3)/XPhos was found to be a superior catalyst for the coupling of 1 with the zinc derivative of 2 to give tert-butyl (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-3-(1-tosyl-1H-pyrrolo[2,3-b]pyridin-3-yl)propanoate derivatives 3 in 69-91% isolated yields. In addition, we have demonstrated that the protecting groups, namely, Ts, Fmoc, and Bu-t, can be easily removed selectively.