Synthesis and Properties of 7‐Substituted 7‐Deazapurine (Pyrrolo[2,3‐d]pyrimidine) 2′‐Deoxyribonucleosides

Heterochiral DNA with Complementary Strands with α-d and β-d Configurations: Hydrogen-Bonded and Silver-Mediated Base Pairs with Impact of 7-Deazapurines Replacing Purines

Heterochiral DNA with hydrogen-bonded and silver-mediated base pairs have been constructed using complementary strands with nucleosides with α-d or β-d configuration. Anomeric phosphoramidites were employed to assemble the oligonucleotides. According to the Tm values and thermodynamic data, the duplex stability of the heterochiral duplexes was similar to that of homochiral DNA, but mismatch discrimination was better in heterochiral DNA. Replacement of purines by 7-deazapurines resulted in stable parallel duplexes, thereby confirming Watson-Crick-type base pairing. When cytosine was facing cytosine, thymine or adenine residues, duplex DNA formed silver-mediated base pairs in the presence of silver ions. Although the CD spectra of single strands with α-d configuration display mirror-like shapes to those with the β-d configuration, the CD spectra of the hydrogen-bonded duplexes and those with a limited number of silver pairs show a B-type double helix almost indistinguishable from natural DNA. Nonmelting silver ion-DNA complexes with entirely different CD spectra were generated when the number of silver ions was equal to the number of base pairs.

Studies on the glycosylation of pyrrolo[2,3-d] pyrimidines with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose: the formation of regioisomers during toyocamycin and 7-deazainosine syntheses

Glycosylation of silylated 4-amino-6-bromo-5-cyano-7H-pyrrolo[2,3-d]pyrimidine (9) with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose (10) under "one-pot" glycosylation conditions (MeCN, TMSOTf) yielded the N-7 isomer 11 together with the N-1 compound 13 (ratio = 2:1). When the same conditions were applied to 4-hydroxy-7H-pyrrolo[2,3-d]pyrimidine (21) the N-3 isomer 22 was the only glycosylation product formed in almost quantitative yield.

7-Functionalized 7-deazapurine ribonucleosides related to 2-aminoadenosine, guanosine, and xanthosine: glycosylation of pyrrolo[2,3-d]pyrimidines with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose

[reaction: see text] The Silyl-Hilbert-Johnson reaction as well as the nucleobase-anion glycosylation of a series of 7-deazapurines has been investigated, and the 7-functionalized 7-deazapurine ribonucleosides were prepared. Glycosylation of the 7-halogenated 6-chloro-2-pivaloylamino-7-deazapurines 9b-d with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose (5) gave the beta-D-nucleosides 11b-d (73-75% yield), which were transformed to a number of novel 7-halogenated 7-deazapurine ribonucleosides (2b-d, 3b-d, and 4b-d) related to guanosine, 2-aminoadenosine, and xanthosine. 7-Alkynyl derivatives (2e-i, 3e-h, or 4g) have been prepared from the corresponding 7-iodonucleosides 2d, 3d, or 4d employing the palladium-catalyzed Sonogashira cross-coupling reaction. The 7-halogenated 2-amino-7-deazapurine ribonucleosides with a reactive 6-chloro substituent (18b-d) were synthesized in an alternative way using nucleobase-anion glycosylation performed on the 7-halogenated 2-amino-6-chloro-7-deazapurines 13b-d with 5-O-[(1,1-dimethylethyl)dimethylsilyl]-2,3-O-(1-methylethylidene)-alpha-D-ribofuranosyl chloride (17). Compounds 18b-d have been converted to the nucleosides 19b-d carrying reactive substituents in the pyrimidine moiety. Conformational analysis of selected nucleosides on the basis of proton coupling constants and using the program PSEUROT showed that these ribonucleosides exist in a preferred S conformation in solution.