Preparation and Reactions of Certain Racemic and Optically Active Cyanohydrins Derived from 2-Chlorobenzaldehyde, 4-Fluorobenzaldehyde, Benzo[d][1,3]-dioxole-5-carbaldehyde and 2,3-Dihydrobenzo[b][1,4]dioxine-6-carbaldehyde. Antimicrobial and in vitro Antitumor Evaluation of the Products

THE CHEMOENZYMATIC reaction of selected aldehydes, ……...namely 2-chlorobenzaldehyde (1a), 4-fluorobenzaldehyde (1b), benzo[d][1,3]dioxole-5-carbaldehyde (1c) and/or 2,3-dihydrobenzo [b] [1,4] dioxine-6-carbaldehyde (1d) with hydrogen cyanide in presence of (R)-oxynitrilase (R)-Pa HNL [EC 4.1.2.10] from almonds, as a chiral catalyst, gave the optically active cyanohydrin enantiomers (R)-2a-c, respectively.  Acetone cyanohydrin (3), was also used, as a transcyanating agent, to give the same products.  The racemic cyanohydrins (R,S)-2a-d have been synthesized, as well, by treating compounds 1a-d with aqueous potassium cyanide solution in presence of a saturated solution of sodium metabisulphite (Na₂S₂O₅).  The optical purity of cyanohydrins (R)-2a-c was determined through their derivatization with (S)-naproxen chloride (S)-5 to the respective diastereomers (R,2S)-6a-c which were obtained in diastereomeric excess (de) values up to 93 % (¹H NMR).  Heating compounds (R)-2a,b and / or their racemic analogues (R,S)-2a-c with concentrated hydrochloric acid gave the respective α-hydroxycarboxylic acids 7a-c.  Moreover, reduction of cyanohydrins (R,S)-2b,c under different conditions resulted in a hydrodecyanation giving the respective  primary alcohols 8a,b. Structures and configurations of the new compounds were confirmed with compatible elementary microanalyses and spectroscopic ( IR, ¹H NMR, ¹³C NMR, MS and single crystal X-ray crystallography) measurements.  The antimicrobial activity of derivatives 6a-d against four bacterial species (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) and two fungi (Aspergillus flavus and Candida albicans) were undertaken.  Moreover, compounds (R,2S)-6b, (R,2S)(S,2S)-6b and (R,2S)−6c were screened for their in virto antitumor activity against three human solid cancer cell lines (HCT 116, HepG2 and MCF-7).  In general, the tested compounds were found inactive or showed weak activities in comparison with the standard drugs.