Mass spectra ofC-nucleosides II. An unusual fragmentation reaction of the heterocyclic moiety of pyrazomycin and some closely related compounds

Pyrazole containing natural products: synthetic preview and biological significance

A large number of structurally diverse natural compounds containing azole nucleus constitute an important class of biologically active heterocycles that are gaining more attention in the field of medicinal chemistry. Among azoles, pyrazoles are rarely found in nature probably due to difficulty in the formation of N-N bond by living organisms. However, they exhibit numerous biological activities, including anti-diabetic, antiviral, anticancer, anti-inflammatory, antibacterial and antifungal activities. The present review is an attempt to understand the chemistry along with medicinal importance of pyrazole containing natural products reported till date which would certainly help the scientific community to bring further developments in the isolation and synthetic methodologies for pyrazole based novel bioactive compounds.

Synthesis of 3-(α- and β-d-arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3-b]pyridazine

Di-O-isopropylidene- and O-methanesulfonyl-protected 1-C-(6-chloro-1,2,4-triazolo[4,3-b]pyridazin-3-yl)pentitols were prepared in three to four steps from D-galactose, D-glucose, D-mannose, and 2,3:5,6-di-O-isopropylidene-alpha-D-mannofuranose. Acid-catalysed treatment of (1S)- and (1R)-1-C-(6-chloro-1,2,4-triazolo[4,3-b]-pyridazin-3-yl)-2,3:4,5-di-O-isopropylidene-1-O-methanesulfonyl-D-arabinitols in refluxing 1,2-dimethoxyethane furnished 3-(alpha- and beta-D-arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3-b]pyridazine, respectively. Several structures, including the structure of the 3-(beta-D-arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3-b]pyridazine, were also determined by single-crystal X-ray diffraction analysis.

Structure of the modified nucleoside Q isolated from Escherichia coli transfer ribonucleic acid. 7-(4,5-cis-Dihydroxy-1-cyclopenten-3-ylaminomethyl)-7-deazaguanosine

The structure of the unknown modified nucleoside Q, which is present in the first position of the anticodons of Escherichia coli tRNA Tyr, tRNA His, tRNA Asn, tRNA Asp, is proposed to be 7-(4,5-cis-dihydroxy-1-cyclopenten-3-ylaminomethyl)-7-deazaguanosine (1). The structure of Q was deduced by means of its uv absorption, mass spectrometry, proton magnetic resonance spectroscopy, and studies of its chemical reactivity. The structure of Q is unique since it is a derivative of 7-deazaguanosine having cyclopentenediol in the side chain at the C-7 position. This is the first example of purine skeleton modification in a nucleoside from tRNA.