Reductive capabilities of different cyanobacterial strains towards acetophenone as a model substrate - Prospect of applications for chiral building blocks synthesis.

Bioreductive capabilities of four morphologically different strains of cyanobacteria have been assessed in this work. Arthrospira maxima, Leptolyngbya foveolarum, Nodularia sphaerocarpa and Synechococcus bigranulatus were applied as catalysts for the reduction of acetophenone to the corresponding chiral phenylethyl alcohol. The process was modified regarding substrate concentration, duration of pre-cultivation period, duration of biotransformation, light regime and glucose addition to the culture media. Obtained results clearly showed that cyanobacteria were active towards acetophenone what resulted in the substrate reduction to (S)-1-phenylethanol with high enantiomeric excess. The reaction efficiency increased with the biotransformation time, but the higher concentration of substrate limited the process yield. Also, all tested strains performed reaction with the highest efficacy under continuous light regime. The most active strains - N. sphaerocarpa and S. bigranulatus carried out the conversion of 1 mM acetophenone with high efficiency of respectively 97.6% and 96.2% after 13 days of biotransformation. A. maxima reached 45.8% of conversion after 13 days of biotransformation whereas L. foveolarum did not exceed 20%. The enantiomeric excesses were respectively 98.8%- A. maxima, 91.7%- L. foveolarum, 72.6%- S. bigranulatus and N. sphaerocarpa 16.2%.

Reductive activity of free and immobilized cells of cyanobacteria toward oxophosphonates-comparative study.

This report, based on the previous studies, compares the reductive activity of different modes of following photobiocatalysts (on laboratory and preparative scale): Arthrospira maxima, Nostoc cf. muscorum and Nodularia sphaerocarpa, toward diethyl esters of 2-oxopropylphosphonate (1), 2-oxo-2-phenylethylphosphonate (2), and 2-oxobutylphosphonate (3). It was confirmed that immobilization in alginate matrix do not affect the activity and viability of the biocatalysts. Corresponding (S)-hydroxyphosphonates (1a-3a) were obtained with similar efficiency compared to the free-cell mode with the yield and of the optical purity e.e respectively (e.g., N. sphaerocarpa experiments): (1) yield: 21 %, e.e. 84 %; (2) yield 97 %, e.e. 97; (3) yield 21 %, e.e. 89 %. Scaling up the processes for the best biocatalyst, N. sphaerocarpa, indicated that the use of free-living cells of cyanobacteria is more effective (640 mg of substrate 2, 44 % of yield, 91 % of e.e.), compared to the column bioreactor packed with immobilized cells of this photobiocatalyst (384 mg of substrate 2, 38 % of yield, 86 % of e.e). In the case of free and immobilized cells of N. cf. muscorum, agitation of the medium was the crucial activity mediator. Shaking culture of free cells of N. cf. muscorum converted the diethyl 2-oxo-2-phenylethylphosphonate (2) with the yield of 43 % (99 % of e.e.) compared to 18 % (99 % of e.e., stationary culture). Immobilized cells of this cyanobacterium were also more active toward (2) under shaking conditions (28 % of yield, 99 % of e.e.) than free ones without agitation.