CONFORMATION OF RIBONUCLEOSIDES IN SOLUTION . EFFECT OF STRUCTURE ON ORIENTATION OF BASE

The conformations of a number of adenosine derivatives in dilute aqueous solution have been investigated, with the aid of measurements of the optical rotatory dispersion, infrared and ultraviolet spectra, and dissociation constants. The compounds studied include adenosine, N1-methyladenosine, 2[image]-adenylic acid, 3[image],5[image]-cyclic adenylic acid, 2[image]-O-methyladenosine, 2[image],3-isopropylide-neadenosine, 5[image]-methyl-thioadenosine, S-adenosylmethionine, and S-adenosylhomocysteine, as well as other adenosine derivatives containing sulfur substituents on the 5[image]-carbon. The introduction of a sulfur atom, of either the thioether or sulfonium type, results in change in sign of the Cotton effect centered around 260 m[mu]. It is proposed that this change is due to an alteration in the conformation of nucleoside. The relevance of these observations to the more general question of the conformation of nucleosides in solution is discussed.