Metabolism of N‐methyl‐amide by cytochrome P450s

Abstract

We report unambiguous proof of the stability of a carbinol intermediate in the case of P450 metabolism of an N‐methylated natural cyclo‐peptide, namely tentoxin. Under mild acidic or neutral conditions, the lifetime of carbinol‐amide is long enough to be fully characterized. This metabolite has been characterized using specifically labeled 14C‐methyl tentoxin isotopomers, HPLC, HPLC‐MS, MS‐MS and NMR. Under stronger acidic conditions, the stability of this metabolite vanishes through deformylation. A theoretical mechanistic investigation reveals that the stability is governed by the accessibility of the nitrogen lone pair and its protonation state. For carbinol‐amines, even in neutral conditions, the energy barrier for deformylation is low enough to allow rapid deformylation. Carbinol‐amide behaves differently. Under neutral conditions, delocalization of the nitrogen lone pair increases the energy barrier of deformylation that is a slow process under such conditions. After protonation, we were able to optimize a deformylation transition that is lower in energy and thus accounts for the lower stability of carbinol‐amides observed experimentally in acidic conditions. Finally, by considering the protocol usually used for extraction and analysis of this type of metabolite, carbinol‐amide may thus be frequently ignored in drug metabolism pathways.

N-Methylamide-structured SB366791 derivatives with high TRPV1 antagonistic activity: toward PET radiotracers to visualize TRPV1

“…From the viewpoint of medicinal chemistry, the N-methyl-derivatization strategy can impart several benefits, such as resistance to metabolizing enzymes, membrane permeability, and biological activity in some cases. [17][18][19] Therefore, we considered that N-methylamide derivatives would be advantageous for obtaining a higher antagonistic activity.…”

“…The 3-methoxy and 3-fluoropropoxy substituents in the promising compounds 2 and 4 were intentionally designed to introduce radioactive [ 11 C]methoxy and [ 18 F]fluoropropoxy groups, respectively, on the oxygen atom of the phenol ring by adopting previously reported 11 C-methylation and 18 Ffluoropropylation strategies. 26,27 According to a previous synthesis of 11 C-labeled SB366791 [ 11 C]1 using the precursor 5, 15 [ 11 C]2 was synthesized using [ 11 C]methyl iodide and N-methylamide-structured phenol precursor 6 in the presence of Cs 2 CO 3 within 37 min, including the reaction time (4 min) and purification process ¶ (Fig.…”

“…[ 11 C]Carbon dioxide was produced by a 14 N(p,α) 11 C nuclear reaction using a Sumitomo CYPRIS HM-12S cyclotron (Sumitomo Heavy Industries) and then converted into [ 11 C]methyl iodide by the reduction of [ 11 C]carbon dioxide with lithium aluminum hydride and iodination with hydroiodic acid using a RIKEN original remote-controlled 11 C-radiolabeling system. 18 O-Enriched water (Taiyo-Nissan) was irradiated with 12 MeV protons in the same cyclotron to generate [ 18 F]fluoride ions. A 18 F-radiolabeling reaction was carried out using a RIKEN original remote-controlled 18 F-radiolabeling system.…”

“…In accordance with the radiopharmaceutical formulation, the desired product [ 18 F]4 was dissolved in a mixed solution (3.0 mL) of saline, propylene glycol, and Tween 80 (volume ratio: 100/10/1) and collected in a sterilized vial. The total synthesis time, including 18 F-labeling reaction, HPLC purification, and radiopharmaceutical formulation, was less than 70 min. The radioactivity of the formulated injection solution of [ 18 F]4 was ≈1.9 GBq, and the molar activity at the end of the synthesis was ≈410 GBq μmol −1 .…”

“…15 According to their report, [ 11 C]1 was insufficient for visualizing TRPV1, although tracer accumulation was observed in the trigeminal nerve. Thus, this issue prompted us to further develop antagonistic compounds with higher TRPV1-binding affinity while considering which chemical structures can be adapted to the incorporation of 11 C or 18 F radionuclides for in vivo PET imaging.…”