The Structure of Pyrimidine Nucleosides Derived from Nucleic Acids

The Structure of Pyrimidine Nucleosides Derived from Nucleic Acids 

Early chemical studies with naturally occurring nucleosides were related primarily to the elucidation of their structures. As a result mainly of the efforts of the Levene group,17 much of the basic information on the structure and chemical properties of nucleosides was already available by 1930. 

Identification of the nitrogenous bases (aglycons) of pyrimidine nucleosides began at the turn of the century, when Kossel and Neumann18 isolated thymine (5-methyluracil) from nucleic acid and showed this pyrimidine to be identical with the nucleosin previously described by Miescher.19 The isolation of cytosine20 [4-amino-2()//)-pyrimidinone] and uracil21 [2,4(1, 3 )-pyrimidinedione] from the nucleic acids came shortly there- 

Of these pyrimidines, uracil and cytosine are constituents of ribonucleic acid, whereas thymine and cytosine are components of deoxyribonucleic acid. It was generally accepted that these nitrogenous heterocycles were the only pyrimidine components of the nucleic acids. The possibility that the nucleic acids might contain moieties other than those described had been voiced by Gulland,26 Chargaff and Vischer,27 and Davidson.28 The 

Thymine and 5-methylcytosine, at first found only as components of deoxyribonucleic acid, have since been discovered in the ribonucleic acid fraction derived from certain microorganisms.42,43 [Uracil, on the other hand, previously demonstrated as a constituent of ribonucleic acid only, has been obtained, as a deoxynucleoside, from an enzymic hydrolyzate of a commercial sample of herring-sperm deoxyribonucleic acid.44 However, this 

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III. The Structure of Pyrimidine Nucleosides Derived from Nucleic Acids.. . . 285... 

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