Spectrophotometric studies of nucleic acid derivatives and related compounds as a function of pH: IV. On the structure of orotidine. A study of N-methylated orotic acids

Abstract

In order to provide a firm basis for the determination of the position of attachment of the sugar moiety to the pyrimidine ring in orotidine, a series of N-methylated orotic acid derivatives have been synthesized and their structure proved by conversion to substances of known structure. The ultraviolet absorption spectra of these N-methylorotic acid derivatives as a function of pH were determined and their “apparent” dissociation constants were measured spectrally. It was shown that these derivatives bear the same spectral relationship to orotic acid as do the N-methylated uracils to uracil. Information relative to the structure of these compounds in aqueous solutions was deduced therefrom. The spectrum of orotidine as a function of pH was presented and shown to be very similar to that for 1-methylorotic acid. The sugar residue of orotidine (and thereby of orotidine-5′-phosphate) is therefore linked at the #1 position of the pyrimidine ring. Metaperiodate oxidation studies have shown that orotidine is a furanoside. The structure of orotidine is, therefore, 1- d-ribofuranosyluracil-6-carboxylic acid.