“…The peptide group formed by Ca,-Na,-C-C" is antiperiplanar and projects straight from the five-membered sugar ring, with torsion angle Ha,-Ca,-Na,-C in syn-periplanar range. This particular atomic arrangement appears to be a characteristic feature of (planar) carboxyl or peptidyl groups attached to the Ca, carbon of furanoses-in 3 '-0acetylnucleosides, a similar situation is found (195,712,713). The conformation of the p-methoxyphenylalanyl moiety is not unusual, with torsion angles N-C,,-CrCy and Na,-C-C,,-C tl in the common extended (ap) and staggered (sc) ranges.…”