P450-catalyzed intramolecular sp3 C-H amination with arylsulfonyl azide substrates

Abstract

The direct amination of aliphatic C-H bonds represents a most valuable transformation in organic chemistry. While a number of transition metal-based catalysts have been developed and investigated for this purpose, the possibility to execute this transformation with biological catalysts has remained largely unexplored. Here, we report that cytochrome P450 enzymes can serve as efficient catalysts for mediating intramolecular benzylic C-H amination reactions in a variety of arylsulfonyl azide compouds. Under optimized conditions, the P450 catalysts were found to support up to 390 total turnovers leading to the formation of the desired sultam products with excellent regioselectivity. In addition, the chiral environment provided by the enzyme active site allowed for the reaction to proceed in a stereo- and enantioselective manner. The C-H amination activity, substrate profile, and enantio/stereoselectivity of these catalysts could be modulated by utilizing enzyme variants with engineered active sites.

Keywords: C—H amination; arylsulfonyl azides; cytochrome P450; enzymatic catalysis; protein engineering; sultams.

Figure 1

Substrate scope of P450 C–H amination catalysts. (A) Tested substrates and corresponding benzosultam products. (B) Measured TTNs for the different P450 variants (see also Table S2).

Scheme 1. Proposed Mechanism for the Formation of the Benzosultam and Benzosulfonamide Products in the P450-Catalyzed Reactions

Figure 2

Close-up view of the active site cavity in the substrate-bound structure of P450_BM3 (pdb 1FAG). The heme cofactor and Thr268 residue are highlighted in yellow and purple, respectively. Active-site positions that are mutated in the P450 variants tested in this study are also labeled (brown, see Table S1). The enzyme-bound substrate (palmitate) and part of the protein structure are not shown for clarity.