3 years ago

Effects of introduction of α-carboxylate, N-methyl, and N-formyl groups on intramolecular cyclization of o-quinone amines: Density functional theory-based study

Effects of introduction of α-carboxylate, N-methyl, and N-formyl groups on intramolecular cyclization of o-quinone amines: Density functional theory-based study
Adhitya Gandaryus Saputro, Ryan Lacdao Arevalo, Hideaki Kasai, Ryo Kishida
o-Quinone amines, which are relevant to various biological processes, can undergo spontaneous intramolecular cyclization (ring closure reaction by amino-terminated hydrocarbon side chain) that deactivates them toward another possible reactions, that is, thiol binding. Density functional theory-based calculation is employed for obtaining the potential energy curves along the CN bond formation in the intramolecular cyclization of various o-quinone amines, viz., dopaminequinone, dopaquinone, N-methyl-dopaminequinone, N-formyl-dopaminequinone, and the corresponding methylene-inserted analogues. The activation barrier is decreased by introduction of α-carboxylate and N-methyl group whereas increased by introduction of N-formyl group. A negative correlation between the activation barriers and the level of highest occupied molecular orbital is pointed out. Furthermore, the methylene-inserted analogues show decreased activation barriers. This is explained by reduction of steric repulsion in the transition state. o-Quinone amines are relevant to various biological processes and undergo intramolecular cyclization (ring closure reaction by amino-terminated hydrocarbon side chain). Density functional theory calculations are useful to investigate their cyclization. The activation barrier for the CN bond formation in the cyclization decreases (increases) by introduction of α-carboxylate and N-methyl (N-formyl) groups. The formation of six-membered rings requires lower activation energies as compared to those of the corresponding five-membered ring formations.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/qua.25445

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