Tri-Cyclic Nucleobase Analogs and their Ribosides as Substrates of Purine-Nucleoside Phosphorylases. II Guanine and Isoguanine Derivatives.

Stachelska-Wierzchowska Stachelska-Wierzchowska,Bzowska Bzowska,Wierzchowski Wierzchowski,Wielgus-Kutrowska Wielgus-Kutrowska,Górka Górka

doi:10.3390/molecules24081493

Abstract

Etheno-derivatives of guanine, O6-methylguanine, and isoguanine were prepared and purified using standard methods. The title compounds were examined as potential substrates of purine-nucleoside phosphorylases from various sources in the reverse (synthetic) pathway. It was found that 1,N2-etheno-guanine and 1,N6-etheno-isoguanine are excellent substrates for purine-nucleoside phosphorylase (PNP) from E. coli, while O6-methyl-N2,3-etheno-guanine exhibited moderate activity vs. this enzyme. The latter two compounds displayed intense fluorescence in neutral aqueous medium, and so did the corresponding ribosylation products. By contrast, PNP from calf spleens exhibited only modest activity towards 1,N6-etheno-isoguanine; the remaining compounds were not ribosylated by this enzyme. The enzymatic ribosylation of 1,N6-etheno-isoguanine using two forms of calf PNP (wild type and N243D) and E. coli PNP (wild type and D204N) gave three different products, which were identified on the basis of NMR analysis and comparison with the product of the isoguanosine reaction with chloroacetic aldehyde, which gave an essentially single compound, identified unequivocally as N9-riboside. With the wild-type E. coli enzyme as a catalyst, N9-β-d- and N7-β-d-ribosides are obtained in proportion ~1:3, while calf PNP produced another riboside, tentatively identified as N6-β-d-riboside. The potential application of various forms of PNP for synthesis of the tri-cyclic nucleoside analogs is discussed.

Highlights

Some tri-cyclic analogs of the natural purine bases and their glycosides show intense fluorescence, what enables their application as fluorescent probes in the investigations of structure and function of nucleic acids (DNA, RNA) and enzymes related to nucleic acid metabolism or utilizing nucleotide cofactors [1,2]
Y-base (3,10-dimethyl-1,N2 -ethenoguanine) [3]. 1,N2 -ethenoguanine is a main product of the slow reaction of chloroacetic aldehyde (CAA) with guanine [5], and one of three main products of the reaction of DNA with the mutagen vinyl chloride [12,20,21,22]
We decided that more convenient way to obtain this isomer would be a much faster reaction of CAA with 2-amino-6-chloropurine riboside [6], which gave a mixture

Summary

Introduction

Some tri-cyclic analogs of the natural purine bases and their glycosides show intense fluorescence, what enables their application as fluorescent probes in the investigations of structure and function of nucleic acids (DNA, RNA) and enzymes related to nucleic acid metabolism or utilizing nucleotide cofactors [1,2]. Other etheno-purine derivatives (see Scheme 1) were prepared but were reported to display rather discouraging emission properties: This refers to the guanine/guanosine derivatives [3,4,5], as well to the products of the analogous reactions of CAA with 2-aminopurine and its riboside [6,7], and. Other etheno-purine derivatives (see Scheme 1) were prepared but were reported to display rather discouraging emission properties: This refers to the guanine/guanosine derivatives [3,4,5],Molecules as well2019, to the products of the analogous reactions of CAA with 2-aminopurine and its riboside of 18. Thorough seems spectral of those and other etheno-derivatives in etheno-derivatives in various aconditions to examination be necessary for further applications.

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Conclusion