Influence of N(1) protonation on the orientation of the N(6) substituent in hypermodified nucleic acid base N6-(N-glycylcarbonyl) adenine

✍ Scribed by Ravindra Tewari

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 179 KB
• Volume: 62
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1997)62:5<551::aid-qua11>3.0.co;2-8

✦ Synopsis

The influence of protonation at N 1 on the conformational preferences Ž .

6 Ž . of the N 6 substituent in the modified nucleic acid base N -N-glycylcarbonyl adenine, gc 6 Ade, was investigated by the quantum chemical perturbative configuration interaction Ž . using localized orbitals PCILO method. The preferred orientation of the glycylcarbonyl Ž . substituent changes on the protonation of N 1 . In the preferred conformation, the Ž . Ž . carbonyl oxygen O 10 is placed on the same side as N 1 H and provides stabilization Ž . Ž . through intramolecular hydrogen bonding of O 10 with HN 1 . The amino acid Ž . component is so oriented that the carboxyl oxygen O 13b is aligned closely with the Ž .

N 6 H direction. Thus, the preferred molecular orientation is further stabilized by Ž . Ž . intramolecular hydrogen bonding involving HN 6 with O 13b . The alternative conformation has 0.5 kcalrmol higher energy than has the preferred conformation. The preferred conformation is about 1 kcalrmol more stable than is the conformation obtained by the flipping of torsion angle ␤ alone, from the favored orientation for the unprotonated gc 6 Ade.