Optical Rotatory Dispersion of Two Pairs of Sequence Isomers of Trinucleotides 1 )

OLIGONUCLEOTIDE STUDIES, PART II. OPTICAL ROTATORY DISPERSION OF TWO PAIRS OF SEQUENCE ISOMERS OF TRINUCLEOTIDES 1) Y. Inoue, S. Aoyagi and K. Nakanishi Department of Chemistry, Tohoku University, Sendai, Japan. (Received in Japan 13 June 1967) Optical rotatory dispersion (ORD) is understood as the most powerful physical method in the characterization of the conformational structures of oligoand polynucleotides of different composition and sequence. For this reason, in recent years, ORD data have been reported for several oligonucleotides 2-7) . However, these studies have been restricted to the observation of the oligonucleotides obtained either from bovine pancreatic ribonuclease I (EC 2.7.7. 16) digestion of ribonucleic acids (RNA) or from a partial degradation of synthetic polynucleotides. Recently, we have succeeded in the isolation in pure form of seven trinucleotides (ApApGp, ApCpGp, ApUpGp, CpApGp, CpCpGp, UpApGp, and UplJpG~)~l out of nine possible trinucleotides’) produced on Taka-Diastase ribonuclease Tl (EC 2.7. 7. 26) digestion of high molecular 1) weight RNA . The purpose of this communication is to report the results of an ORD 10) study of the two pairs of sequence isomers, ApCpGp and CpApGp, and ApUpGp and UpApGp. The fact that no ORD work has been reported previously in the structural characterization of trinucleotides having the guanylic acid moiety as the terminal residue represents a missing link in study, to date, of oligonucleotides as models of nucleic acids. Although the absorption spectra are, in general, not sensitive to basesequence, a detailed analysis of these spectra together with hyperchromicity measurements makes it possible to determine nucleotide sequence of diand 1) trinucleotides . However, the ORD criteria for the identification of sequence isomers are more convenient as can be clearly seen in Fig. 1. Since it is evident from the literature 4.7) that a 3’ terminal phosphate does not substan-