The Biomimetic Synthesis of Polyarylated Fluorenes, Relevant to Selaginellaceae Polyphenols, Leading to the Spontaneous Formation of Stable Radicals.

This work reports a biomimetic synthesis of polyarylated fluorene derivatives. The molecules are formed via intramolecular electrophilic aromatic substitution, resembling a cyclization leading towards the natural selaginpulvilins from selaginellins. The scope of the reaction was investigated, and the products were obtained in 60-95 % yields. Some of the compounds decompose to a stable radical. We investigated the nature and the origin of the radical using experimental methods, including EPR or electrochemical measurements, as well as theoretical methods, such as DFT calculations. Based on our observations, we hypothesize, that phenoxy radicals are formed in the first instance, which however undergo internal rearrangement to thermodynamically more stable carbon-centered radicals. The preliminary data also show the cytotoxic properties of some of the molecules.

A Catharanthus roseus Fe(II)/α-ketoglutarate-dependent dioxygenase catalyzes a redox-neutral reaction responsible for vindolinine biosynthesis.

The Madagascar's periwinkle is the model plant for studies of plant specialized metabolism and monoterpenoid indole alkaloids (MIAs), and an important source for the anticancer medicine vinblastine. The elucidation of entire 28-step biosynthesis of vinblastine allowed further investigations for the formation of other remarkably complex bioactive MIAs. In this study, we describe the discovery and characterization of vindolinine synthase, a Fe(II)/α-ketoglutarate-dependent (Fe/2OG) dioxygenase, that diverts assembly of tabersonine to vinblastine toward the formation of three alternatively cyclized MIAs: 19S-vindolinine, 19R-vindolinine, and venalstonine. Vindolinine synthase catalyzes a highly unusual, redox-neutral reaction to form a radical from dehydrosecodine, which is further cyclized by hydrolase 2 to form the three MIA isomers. We further show the biosynthesis of vindolinine epimers from tabersonine using hydrolase 2 catalyzed reverse cycloaddition. While the occurrence of vindolinines is rare in nature, the more widely found venalstonine derivatives are likely formed from similar redox-neutral reactions by homologous Fe/2OG dioxygenases.

Tetrodotoxin: History, Biology, and Synthesis.

This review provides a comprehensive coverage of the history, biology and chemistry of tetrodotoxin (TTX). It traces the origin of this remarkable molecule all the way back to the ancient Chinese medicine records. The discovery of biological activity, isolation, and a brief overview of structure elucidation are summarized. Next, the biology of TTX is discussed, primarily in the context of its activity in the sodium channels, its anesthetic properties, and its potential use in cancer treatment or drug addiction. Biosynthesis of TTX is covered before the discussion of the total syntheses. All total, formal or partial syntheses are covered but those total syntheses that have been discussed in previous reviews are only briefly summarized. Finally, the synthesis of natural and unnatural derivatives is surveyed, and a conclusion and outlook are provided for this very extensive field of endeavor. To the best of our knowledge the literature coverage is complete up to December 2018.

Solution of the multistep pathway for assembly of corynanthean, strychnos, iboga, and aspidosperma monoterpenoid indole alkaloids from 19E-geissoschizine.

Monoterpenoid indole alkaloids (MIAs) possess a diversity of alkaloid skeletons whose biosynthesis is poorly understood. A bioinformatic search of candidate genes, combined with their virus-induced gene silencing, targeted MIA profiling and in vitro/in vivo pathway reconstitution identified and functionally characterized six genes as well as a seventh enzyme reaction required for the conversion of 19E-geissoschizine to tabersonine and catharanthine. The involvement of pathway intermediates in the formation of four MIA skeletons is described, and the role of stemmadenine-O-acetylation in providing necessary reactive substrates for the formation of iboga and aspidosperma MIAs is described. The results enable the assembly of complex dimeric MIAs used in cancer chemotherapy and open the way to production of many other biologically active MIAs that are not easily available from nature.

A novel approach for HPLC determination of 2-cynaoacetamide using derivatization procedure with 2-hydroxyacetophenone as a new useful derivatization reagent.

A novel and sensitive derivatization procedure for the determination of 2-cynaoacetamide in pharmaceutical samples using liquid chromatography with the fluorescence detection was discovered. The method is based on derivatization of 2-cynaoacetamide using 2-hydroxyacetophenone as a new derivatization reagent. The product of derivatization reaction was isolated and characterized using spectroscopic techniques namely LC-MS, NMR and IR. The structure of 2-cyanoacetamide derivative was unambiguously assigned as a 2-amino-4-phenylfuran-3-carboxamide. Two derivatization systems were optimized in terms of reaction temperature, reaction time, pH and concentration of 2-hydroxyacetophenone, and a new pre- and post-derivatization HPLC methods were developed. The separations on HPLC with pre-column derivatization were accomplished using stationary phase based on a XBridge C18 column (100×4.6, 3.5µm) and isocratic elution using the mobile phase acetonitrile - 0.1% formic acid (30:70, v/v). The separations on the HPLC with post-column derivatization were performed on stationary phase on a TSKgel Amide-80 column (150×4.6mm, 3µm). The mobile phase was a mixture of acetonitrile, methanol and 10mM sodium formate buffer at pH=4.5 in ratio 3:2:95 (v/v). Both HPLC methods were fully validated in terms of linearity, sensitivity (limit of detection and limit of quantification), accuracy and precision according to ICH guidelines. The pre-column derivatization method was linear in the range 1.1-2000µg/l with method accuracy≥98.2% and method precision RSD≤4.8%. The post-column derivatization method was linear in the range 12-2000µg/l. Method accuracy≥96.3% and method precision RSD≤3.5%. Proposed new methods were proved to be highly sensitive, simple and rapid, and were successfully applied to the determinations of 2-cynaoacetamide in pregabalin.

Kinetics and mechanism of the base-catalyzed rearrangement and hydrolysis of ezetimibe.

The pH-rate profile of the pseudo-first-order rate constants for the rearrangement and hydrolysis of Ezetimibe giving (2R,3R,6S)-N,6-bis(4-fluorophenyl)-2-(4-hydroxyphenyl)-3,4,5,6-tetrahydro-2H-pyran-3-carboxamide (2) as the main product at pH of less than 12.5 and the mixture of 2 and 5-(4-fluorophenyl)-5-hydroxy-2-[(4-fluorophenylamino)-(4-hydroxyphenyl)methyl]-pentanoic acid (3) at pH of more than 12.5 in aqueous tertiary amine buffers and in sodium hydroxide solutions at ionic strength I = 0.1 mol L(-1) (KCl) and at 39 °C is reported. No buffer catalysis was observed and only specific base catalysis is involved. The pH-rate profile is more complex than the pH-rate profiles for the hydrolysis of simple ß-lactams and it contains several breaks. Up to pH 9, the log k(obs) linearly increases with pH, but between pH 9 and 11 a distinct break downwards occurs and the values of log k(obs) slightly decrease with increasing pH of the medium. At pH of approximately 13, another break upwards occurs that corresponds to the formation of compound 3 that is slowly converted to (2R,3R,6S)-6-(4-fluorophenyl)-2-(4-hydroxyphenyl)-3,4,5,6-tetrahydro-2H-pyran-3-carboxylic acid (4). The kinetics of base-catalyzed hydrolysis of structurally similar azetidinone is also discussed.

Whole-cell oxidation of omeprazole sulfide to enantiopure esomeprazole with Lysinibacillus sp. B71.

Production of enantiopure esomeprazole by biocatalysis is of great demand by pharmaceutical industry. A Gram-positive bacterium oxidizing omeprazole sulfide 1a (5-methoxy-2-[((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)thio]-1H-benzoimidazole) to (S)-sulfoxide esomeprazole 2a (S)-5-methoxy-2-[(4-methoxy-3,5-dimethylpyridin-2-yl) methylsulfinyl]-3H-benzoimidazole was isolated from soil polluted with elemental sulfur. The strain exhibited the highest identity with the genus Lysinibacillus and catalyzed oxidation of 1a into enantiopure esomeprazole with conversion of 77% in a stirred bioreactor, fed-batch culture. No consecutive oxidation of (S)-sulfoxide to sulfone was observed during whole-cell catalysis. The unique characteristics of the catalyst provide a solid basis for further improvement and development of sustainable green bioprocess.

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism, and optical rotation: the iso-schizozygane alkaloids isoschizogaline and isoschizogamine.

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the concerted application of DFT calculations of VCD, ECD, and OR to the determination of the ACs of the isoschizozygane alkaloid natural products, isoschizogaline, and isochizogamine, whose ACs have not previously been determined. The ACs of naturally occurring (-)-isoschizogaline and (-)-isoschizogamine, are both determined definitively to be 2R, 7R, 20S, 21S.

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism and optical rotation: the schizozygane alkaloid schizozygine.

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the first concerted application of DFT calculations of VCD, ECD, and OR to the determination of the AC of a natural product whose AC was previously undetermined. The natural product is the alkaloid schizozygine, isolated from Schizozygia caffaeoides. Comparison of DFT calculations of the VCD, ECD, and OR of schizozygine to experimental data leads, for each chiroptical technique, to the AC 2R,7S,20S,21S for the naturally occurring (+)-schizozygine. Three other alkaloids, schizogaline, schizogamine, and 6,7-dehydro-19beta-hydroxyschizozygine, have also been isolated from S. caffaeoides and shown to have structures closely related to schizozygine. Assuming a common biosynthetic pathway, their ACs are defined by that of schizozygine.

Synthesis of latanoprost diastereoisomers.

A new synthesis of latanoprost diastereoisomers is described which utilizes a highly stereoselective Michael addition of higher-order cuprate to a chiral cyclopentenone derived from G-lactone in the crucial skeleton-forming step.