Dihydroflavonols from Cedrus deodara

The identification of taxifolin and structure elucidation of cedeodarin (6-methyltaxifolin), dihydromyricetin, cedrin (6-methyldihydromyricetin) and cedrinoside from cedar wood are described.     

Rhynchospermin. A prenylated flavanol from Rhynchosia cyanosperma

A new flavanol has isolated from the leaves of Rhynchosia cyanosperma and identified as 8-C-prenylquercetin 7,4′-dimethyl ether (rhynchospermin).     

Tirumalin,a new prenylated dihydroflavonol from Rhynchosia cyanosperma

A new dihydroflavonol has been isolated together with the known flavonol-O- glycosides, rutin and kaempferol-3-rutinoside, and (+)-pinitol from the leaves of R. cyanosperma Benth. The dihydroflavonol was identified as (+)-(2R, 3R)-8-C-prenyltaxifolin-7, 4′-dimethyl ether on the basis of spectroscopic studies and the compound given the trivial name tirumalin.     

Erythrisenegalone,a prenylated-flavanone from Erythrina senegalensis

The isolation of a new prenylated flavanone, erythrisenegalone, from the stem-bark of Erythrina senegalensis is described. Its structure was established by spectroscopic methods and a few chemical transformations.     

Veprisilone,a prenylated 2-quinolone,and limonin from Vepris louisii

A new 2-quinolone alkaloid, veprisilone, isolated from the trunk bark of Vepris louisii has been characterized as 3-(3-hydroxy-3-methyl-2-oxobutyl)- 4,7,8-trimethoxy-1-methyl-2-quinolone from spectral and chemical data. Limonin was also identified in the extracts.     

Structural insights into UbiD reversible decarboxylation

The ubiquitous UbiX-UbiD system is associated with a wide range of microbial (de)carboxylation reactions. Recent X-ray crystallographic studies have contributed to elucidating the enigmatic mechanism underpinning the conversion of α,β-unsaturated acids by this system. The UbiD component utilises a unique cofactor, prenylated flavin (prFMN), generated by the bespoke action of the associated UbiX flavin prenyltransferase. Structure determination of a range of UbiX/UbiD representatives has revealed a generic mode of action for both the flavin-to-prFMN metamorphosis and the (de)carboxylation. In contrast to the conserved UbiX, the UbiD superfamily is associated with a versatile substrate range. The latter is reflected in the considerable variety of UbiD quaternary structure, dynamic behaviour and active site architecture. Directed evolution of UbiD enzymes has taken advantage of this apparent malleability to generate new variants supporting in vivo hydrocarbon production. Other applications include coupling UbiD to carboxylic acid reductase to convert alkenes into α,β-unsaturated aldehydes via enzymatic CO₂ fixation.