Evaluation of the hydrogen bond energy of base pairs formed between substituted 9-methyladenine derivatives and 1-methyluracil by use of molecular orbital theory.

Systematic substituent effects on the stability of the hydrogen bonding between substituted 9-methyladenine derivatives (Ax) and 1-methyluracil (U) were studied by ab initio molecular orbital theory. Predicted substituent effects on the hydrogen bond energies of Ax-U base pairs were in good agreement with those observed for experimental binding constants. Ab initio calculation is effective for evaluation of the stability of the hydrogen-bonding pairs of chemically modified nucleic acid base analogues. In contrast to the substitution effect of uracil on hydrogen bond energies of A-Ux base pairs, it is difficult to systematically interpret the substitution effect of adenine derivatives for Ax-U base pairs.     

Synthesis of branched ribonucleotides

A synthetic strategy for branched ribonucleotides, which have recently been discovered, was described. A fully protected adenosine unit (5) having the tris (4,5-dichlorophthalimido)trityl (CPTr), bis(anilino)phosphoryl (BAP), and bis(phenylthio)phosphoryl (BPTP) groups as the 5'-, 2'-, and 3'-hydroxyl protecting groups, respectively, was synthesized from adenosine by a five-step reaction involving a new method for the 2'-O-phosphorylation by the use of hexaethylphosphorous triamide. The selective deprotection of appropriate protecting groups from 5 followed by stepwise condensation with two different ribonucleoside derivatives (7 and 10) gave a protected branched ribonucleotide (11) via a 3'-phosphorylated 2'-5' dinucleotide (8). Deprotection of 11 and 8 gave a branched trinucleotide (12) and 3'-phosphorylated dinucleotide (13).     

A solution to the problem of 3'----2'-O-phosphoryl migration in oligoribonucleotide synthesis

Oligoribonucleotides were obtained without contamination of 2'-5' linked regioisomers by means of polymer support when Thp group was employed as 2'-hydroxyl protecting group.     

Chemical synthesis of capped RNA fragments and their ability to complex with eukaryotic ribosomes

In other to examine the binding ability of the 5'-terminal part of eukaryotic mRNA to 80S ribosome, several kinds of oligoribonucleotides, pA-U-G, m7G5'pppA-U-G, m7G5'pppG-U, m7G5'pppA-U-G-A-C-C, were synthesized chemically. The binding experiments of oligonucleotides to 80S ribosome showed that the capped structure as well as AUG are essential for ribosome binding, and the efficiency is enhanced by the 5'-leader sequence if it would include complementary sequence to the 3'-terminal part of 18S rRNA.     

Chemical synthesis of branched RNAs: a new method for construction of synthetic units for branched RNAs by use of 2'-phosphorylation on the basis of steric control.

A 3',5'-unprotected 2'-O-bis(tert-butoxy)-phosphinyl-6-N-benzoyladenosine derivative was prepared as a key intermediate for the synthesis of branched RNAs, and used for construction of building units from which chain elongation in any of 2'-, 3'-, and 5'-directions would be possible. From this synthetic intermediate, 2'-phosphorylated ApC dimer was also synthesized.