ABSTRACT
A concise chemoenzymatic route toward enantiomerically enriched active pharmaceutical ingredients (API) - diprophylline and xanthinol nicotinate - is reported for the first time. The decisive step is an enantioselective lipase-mediated methanolysis of racemic chlorohydrin-synthon acetate, namely 1-chloro-3-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)propan-2-yl acetate, performed under kinetically-controlled conditions on a preparative 500 mg-scale. The best results in terms of reaction enantioselectivity (E = 14) were obtained for the enantiomers resolution performed with lipase type B from Candida antarctica immobilized on acrylic resin (CAL-B, Novozym 435) suspended in homophasic acetonitrile-methanol mixture. The elaborated biocatalytic system furnished the key chlorohydrin intermediate (in 71% ee and 38% yield), which was then smoothly converted into enantioenriched active agents: (R)-(-)-diprophylline (57% ee) and (S)-(+)-xanthinol nicotinate (65% ee). To support the assignment of absolute configurations of EKR-products as well as to confirm the stereochemical outcome of the remaining reaction steps, docking studies toward the prediction of enantiomers binding selectivity in CAL-B active site as well as the respective chemical correlations with enantiomerically enriched analytical standards obtained from commercially available (R)-(-)-epichlorohydrin, were applied. In addition, single-crystal X-ray diffraction (XRD) analyses were performed for the synthesized optically active APIs furnishing by this manner a first crystal structures of nicotinic acid salt of xanthinol.
Subject(s)
Dyphylline/chemical synthesis , Xanthinol Niacinate/chemical synthesis , Basidiomycota/enzymology , Biocatalysis , Dyphylline/metabolism , Enzymes, Immobilized , Esterification , Fungal Proteins/chemistry , Fungal Proteins/metabolism , Hydrogen Bonding , Hydrolysis , Lipase/chemistry , Lipase/metabolism , Molecular Docking Simulation , Protein Binding , Stereoisomerism , Xanthinol Niacinate/metabolismABSTRACT
Bioavailability (therapeutic blood levels) and tolerance of two 500-mg xanthinol nicotinate retard tablet forms and one 1-g xanthinol nicotinate retard tablet (Complamin special) were tested in 11 (12) healthy volunteers. Despite the fact that both 500-mg retard tablets had different in vitro release rates the blood levels in man were similar. These results suggest that in vitro release rates of tablets do not predict corresponding blood levels in man. The tablet with a lower release rate also showed a distinctly lower flush rate. In respect to bioavailability and tolerance the 1-g xanthinol nicotinate retard tablet was comparable with corresponding dosages of 500-mg retard tablets. The dosage given was 2 X 500 mg or 1 g xanthinol nicotinate t.i.d. over a period of 10 days each.