Synthesis of ¹³C, ¹⁵N‐enriched α‐dicarbonyl model adducts to determine the utility of ¹³c and ¹⁵N NMR for studying mechanism‐based inactivation of cytochromes P‐450 by substituted dichloroacetamides

To determine the feasibility of using NMR to study the inactivation of cytochromes P‐450 by dichloroacetamide‐containing mechanism‐based inactivators, ¹³C, ¹⁵N‐enriched compounds were synthesized, modeling adducts between the nucleophilic side‐chains of cysteine, lysine, serine (threonine) and tyrosine and the α‐aminooxoacyl chloride that presumably results from enzymatic conversion of a dichloroacetamide‐containing inhibitor. ¹³C chemical shifts of the carbonyls attached to the nucleophiles easily distinguish the model cysteine adduct (δ 192.3) from the other adducts (δ 159.6–161.8). Although the other adducts cannot be distinguished at this carbon, the carbonyl attached to the ¹⁵N two bonds away can distinguish the lysine mimic (δ 161.2 or 161.3) from the serine (threonine) and tyrosine mimics (δ 156.1–158.1). These assignments were made by comparing ¹⁵N/¹³C J values and were confirmed by solid‐state rotational echo double resonance (REDOR) studies. Finally, aminooxo‐¹⁵N chemical shifts three bonds removed from the nucleophile can distinguish adducts formed to lysine (δ 108.3), cysteine (δ 104.8) and oxygen‐containing side‐chains (δ 112.8–113.9).