Does the Intramolecular Hydrogen Bond Affect the Spectroscopic Properties of Bicyclic Diazole Heterocycles?

Paweł Misiak,Andrzej Łapiński,Alina T Dubis

doi:10.1155/2018/1048157

Abstract

The formation of an intramolecular hydrogen bond in pyrrolo[1,2-a]pyrazin-1(2H)-one bicyclic diazoles was analyzed, and the influence of N-substitution on HB formation is discussed in this study. B3LYP/aug-cc-pVDZ calculations were performed for the diazole, and the quantum theory of atoms in molecules (QTAIM) approach as well as the natural bond orbital (NBO) method was applied to analyze the strength of this interaction. It was found that the intramolecular hydrogen bond that closes an extra ring between the C=O proton acceptor group and the CH proton donor, that is, C=O⋯H–C, influences the spectroscopic properties of pyrrolopyrazine bicyclic diazoles, particularly the carbonyl frequencies. The influence of N-substitution on the aromaticity of heterocyclic rings is also discussed in this report.

Highlights

Pyrrolo[1,2-a]pyrazin-1(2H)-ones are an important class of natural organic compounds synthesized by many grassassociated endophytic fungi [1, 2]
Pyrrolopyrazinones can be used as structural models for studying the release mechanism, metabolism, structure of chemical compounds removed from plant tissues, and the mechanism of anti-insect activity [6]
Three sets of samples of pyrrolopyrazinone systems which differ in the R2 substituent may be selected here; the sample where R2 = CH3 (2, 5, 8, 11, 14, 17, and 20), R2 = CH2Cl (3, 6, 9, 12, 15, 18, and 21), and the sample where R2 = CHCl2 (4, 7, 10, 13, 16, 19, and 22)

Summary

Introduction

Pyrrolo[1,2-a]pyrazin-1(2H)-ones are an important class of natural organic compounds synthesized by many grassassociated endophytic fungi [1, 2]. The ecological significance of pyrrolopyrazinones is related to their feeding deterrent activity. These alkaloids produced by endophytes provide protection of the host plant from herbivores as found in a large number of grass/endophyte associations [4]. In the field of applied ecology, it is important to recognize natural chemical agents that control herbivorous insects [5]. Due to these properties, pyrrolopyrazinones can be used as structural models for studying the release mechanism, metabolism, structure of chemical compounds removed from plant tissues, and the mechanism of anti-insect activity [6]

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Conclusion