'Structural constraints in cyanobacteria-mediated whole-cell biotransformation of methoxylated and methylated derivatives of 2'-hydroxychalcone.

Halophilic and freshwater strains of cyanobacteria representing the Oscillatoriales, Nostocales, Chroococcales, and Synechococcales orders of Cyanophyta were examined to determine (i) the resistance of their cultures when suppressed by the presence of exogenous methoxylated and methylated derivatives of 2'-hydroxychalcone, (ii) morphological changes in cells treated with the tested chalcones and, most importantly, (iii) whether these photoautotrophic microorganisms transform chalcone derivatives in a structure- or strain-dependent manner. The growth of cyanobacterial cultures depended on chalcone derivatives and the strain; nevertheless, trends for correlations between these parameters are difficult to determine. The exposure of cyanobacteria to the tested chalcones revealed severe membrane damage that was consistent with the disruption of membrane integrity. All examined blue-green algae transformed methoxy derivatives of 2'-hydroxychalcone via hydrogenative bio-reduction and formed the corresponding hydroxydihydro derivatives with various efficiencies (≤1 - 70%), depending more on the structure than on the strain. We observed dependency of the routes and efficiency of biohydrogenation of tested chalcones on the location of the methoxyl substituent and, to a lesser extent, on cyanobacterial strains. 2'-hydroxy-4″-methylchalcone was also converted by cyanobacteria to various products, amongst which the most interesting were 2'-ethoxy derivatives. The final products of biocatalytic transformation were extracted from the cyanobacterial media, separated by high performance thin-layer chromatography (HPTLC) and identified by a combination of liquid chromatography-tandem mass spectrometry (LC-MS/MS technique) and one-dimensional (1D 1H and 13C) and two-dimensional (2D HSQC and COSY) nuclear magnetic resonance (NMR) spectroscopy.