USE OF NMR SPECTROSCOPY FOR THE STUDY OF 2,4-DIOXOAND 4-IMINO-2-OXO-3-PHENYL-5-R-6-R′-THIENO[2,3-d]PYRIMIDINES

Abstract

Thieno[2,3-d]pyrimidine derivatives represent a promising class of heterocyclic compounds with a broad spectrum of biological activity, which necessitates the development of reliable methods for their structural identification. Nuclear magnetic resonance (NMR) spectroscopy remains the most informative tool for elucidating the structure of such compounds; however, the systematization of spectral data for 2,4-dioxo- and 4-imino-2-oxo- derivatives is still insufficiently developed. The aim of this study is to systematize and critically analyze current advances in the application of nuclear magnetic resonance methods for determining the structures of 2,4-dioxo- and 4-imino-2-oxo-3-phenyl-5-R-6-R′-thieno[2,3-d] pyrimidines and to identify correlations between the chemical shifts of signals and the structural features of the investigated compounds. The research methods include the analysis of scientific publications devoted to the use of one- and two-dimensional ¹H and ¹³C NMR spectroscopy for the identification and structural characterization of thieno[2,3-d]pyrimidine derivatives, the systematization of spectral data depending on the nature of substituents at positions 2, 3, 4, 5, and 6 of the pyrimidine and thieno rings, and the generalization of information concerning correlations between spectral parameters and the spatial structures of the molecules. The scientific novelty of this study lies in the comprehensive generalization of the spectral characteristics of a wide range of 2,4-dioxo- and 4-imino-2-oxo-thieno[2,3-d]pyrimidine derivatives, the identification of specific features of their NMR spectra depending on the electronic effects of substituents, and the establishment of diagnostic criteria for the unambiguous identification of the structure and configuration of the studied heterocyclic systems. Conclusions. The analysis of the available scientific data indicates that NMR spectroscopy is the most informative method for determining the structure of 2,4-dioxo- and 4-imino-2-oxo-3-phenyl-5-R-6-R′-thieno[2,3-d]pyrimidines. It allows for precise identification of substituent positions, confirmation of the heterocyclic system’s framework, and determination of the spatial configuration of the molecules. The systematization of spectral characteristics provides a foundation for predicting the chemical shifts of new derivatives and for optimizing the methods of their synthesis and identification.