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PHOTOCHEMISTRY OF CYTOSINE NUCLEOSIDES AND NUCLEOTIDES—III. MONO‐ AND DI‐ METHYLAMINO ANALOGUES
Author(s) -
Fikus M.,
Wierzchowski K. L.,
Shugar D.
Publication year - 1962
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1962.tb08108.x
Subject(s) - chemistry , cytosine , pyrimidine , protonation , nucleotide , ring (chemistry) , adduct , quantum yield , nucleobase , stereochemistry , alkylation , photochemistry , organic chemistry , dna , catalysis , biochemistry , ion , physics , quantum mechanics , fluorescence , gene
Summary An investigation has been made of the photochemical (2537 A) behaviour in aqueous medium of mono‐ and dialkylamino substituted cytosines, their nucleosides and nucleotides. The principal reaction in all instances is photohydration, the photoproducts being the 5‐hydro‐6‐hydroxy derivatives of the parent compounds, as for cytosine analogues with a free amino group. Alkylation of the amino group results in a decrease in quantum yield for photoproduct formation of two orders of magnitude; but the resulting photoproducts are much more stable. In the case of the free bases, the increased stability of the photo‐products has made it possible to confirm unequivocally the previous proposal that the photoproducts of cytosine and 1 ‐methylcytosine are also the hydrated derivatives. In the case of the glycosides, the stability of the photoproduct of 2′: 3′‐0‐isopropylidene‐mono‐methylaminocytidine is such as to offer a possibility of a direct NMR check as to whether the hydroxyl of the photo‐adduct is on the 6 position of the pyrimidine ring. The enhanced stability of the protonated forms of the photoproducts has been interpreted in terms of the conformation of the cytosine ring. The absorption spectrum of 173‐dimethylcytosine in acid medium supports the contention that protonation of the cytosine ring occurs on the N, ring nitrogen. Etherification of phosphoester hydroxyls was utilized to examine in greater detail the role of the phosphate groups in the stability of the photoproducts of cytosine nucleotides as a function of pH. The results are all discussed in relation to the photochemistry of nucleic acids.