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.