Synthesis and Characterization of Cyclotriphosphazenes Bearing Six Bile Acid Arms

Four novel cyclotriphosphazene bile acid derivatives (1 - 4) were prepared starting from hexakis[4- (chloromethyl)phenoxy]cyclotriphosphazene (8) as the scaffold. The structures of the compounds were defined by elemental analysis, IR and 1H, 13C and 31P NMR spectroscopy.

One-pot, two-step desymmetrization of symmetrical benzils catalyzed by the methylsulfinyl (dimsyl) anion

Symmetrical-to-unsymmetrical benzil conversion is realized by a one-pot two-step procedure involving a chemoselective cross-benzoin reaction followed by microwave-assisted oxidation of the benzoylated benzoin intermediate.

A combined kinetic and thermodynamic approach for the interpretation of continuous-flow heterogeneous catalytic processes

The heterogeneous proline-catalyzed aldol reaction was investigated under continuous-flow conditions by means of a packed-bed microreactor. Reaction-progress kinetic analysis (RPKA) was used in combination with nonlinear chromatography for the interpretation, under synthetically relevant conditions, of important mechanistic aspects of the heterogeneous catalytic process at a molecular level. The information gathered by RPKA and nonlinear chromatography proved to be highly complementary and allowed for the assessment of optimal operating variables. In particular, the determination of the rate-determining step was pivotal for optimizing the feed composition. On the other hand, the competitive product inhibition was responsible for the unexpected decrease in the reaction yield following an apparently obvious variation in the feed composition. The study was facilitated by a suitable 2D instrumental arrangement for simultaneous flow reaction and online flow-injection analysis.

Elicited Teucrium chamaedrys cell cultures produce high amounts of teucrioside, but not the hepatotoxic neo-clerodane diterpenoids

Teucrium chamaedrys, one of the most common and investigated species of the genus Teucrium, has been used for centuries in traditional medicine for many purposes. Its phytochemical components comprise, among others, phenylethanoid glycosides (PGs) and neo-clerodane diterpenoids. Several reports have demonstrated a wide range of beneficial biological and pharmacological activities of the phenylethanoid components, while the diterpenes were shown to be strongly hepatotoxic. In this work, in vitro cultures were established from leaf explants of T. chamaedrys. Both solid (callus) and liquid (cell suspension) cultures maintained the capacity to produce PGs, with teucrioside (TS) representing the most abundant one. Cell suspensions had a lower TS content than that found in leaf extracts, but higher than that of calli. An NMR-based metabolomics approach was used to compare the product profile of intact plants vs. cell suspension cultures, and results showed that neo-clerodane diterpenes, present in the intact plant, were not detected in cell cultures. Several elicitors were supplied to cell cultures with the aim of increasing TS production, and elicitation was tested at different growth phases and by exposing cells for different periods. Methyl jasmonate and fungal mycelia from Trichoderma viridae and Fusarium moniliforme were able to significantly increase TS production if supplied at the early-exponential growth phase for 24h. Based on the proposed link between proline and the phenylpropanoid pathways, proline accumulation in cell cultures was followed throughout a 14-day culture period, showing that it strictly reflected that of TS production. Moreover, exogenously supplied proline, and its analogue hydroxyproline, turned out to be very effective in increasing teucrioside production.

Thiazolium-catalyzed intermolecular Stetter reaction of linear and cyclic alkyl α-diketones

An efficient method for the N-heterocyclic carbene (NHC)-catalyzed conjugate addition of acetyl anions to various α,β-unsaturated acceptors (Stetter reaction) has been optimized by using 2,3-butandione (biacetyl) as an alternative surrogate of acetaldehyde. The disclosed procedure proved to be compatible with microwave dielectric heating for reaction time reduction and with the use of different linear α-diketones as acyl anion donors (e.g. 3,4-hexanedione for propionyl anion additions). Moreover, the unprecedented umpolung reactivity of cyclic α-diketones in the atom economic nucleophilic acylation of chalcones is herein presented. Mechanistic aspects of the thiazolium-based catalysis involving linear and cyclic α-diketone substrates are also discussed.

7alpha- and 12alpha-Hydroxysteroid dehydrogenases from Acinetobacter calcoaceticus lwoffii: a new integrated chemo-enzymatic route to ursodeoxycholic acid

We report the very efficient biotransformation of cholic acid to 7-keto- and 7,12-diketocholic acids with Acinetobacter calcoaceticus lwoffii. The enzymes responsible of the biotransformation (i.e. 7alpha- and 12alpha-hydroxysteroid dehydrogenases) are partially purified and employed in a new chemo-enzymatic synthesis of ursodeoxycholic acid starting from cholic acid. The first step is the 12alpha-HSDH-mediated total oxidation of sodium cholate followed by the Wolf-Kishner reduction of the carbonyl group to chenodeoxycholic acid. This acid is then quantitatively oxidized with 7alpha-HSDH to 7-ketochenodeoxycholic acid, that was chemically reduced to ursodeoxycholic acid (70% overall yield).

Enantioselective Baeyer–Villiger Oxidation of Bicyclo[3.2.0]hept-2-en-6-One with Fungi: Optimization of Biotransformation and Use of TiO2 as Support of Cell Growth

Fungi from Amazonian forest soil (Ecuador) and an Italian factory were screened for Baeyer-Villiger (BV) oxidation of bicyclo [3.2.0]hept-2-en-6-one to 2-oxabicyclo[3.3.0]oct-6-en-3-one (Corey's lactone). Isolates of Fusarium sp. and F. solani produced the (+)-(1R,5S)-lactone while isolates of Aspergillus terricola and A. amazonicus afforded the (-)-(1S,5R)-lactone. Highest conversions (85% yield and 70% enantiomeric excess) were obtained with A. amazonicus grown in presence of 2.7 mM titanium dioxide.

Xanthomonas maltophilia CBS 897.97 as a source of new 7beta- and 7alpha-hydroxysteroid dehydrogenases and cholylglycine hydrolase: improved biotransformations of bile acids

The paper reports the partial purification and characterization of the 7beta- and 7alpha-hydroxysteroid dehydrogenases (HSDH) and cholylglycine hydrolase (CGH), isolated from Xanthomonas maltophilia CBS 897.97. The activity of 7beta-HSDH and 7alpha-HSDH in the reduction of the 7-keto bile acids is determined. The affinity of 7beta-HSDH for bile acids is confirmed by the reduction, on analytical scale, to the corresponding 7beta-OH derivatives. A crude mixture of 7alpha- and 7beta-HSDH, in soluble or immobilized form, is employed in the synthesis, on preparative scale, of ursocholic and ursodeoxycholic acids starting from the corresponding 7alpha-derivatives. On the other hand, a partially purified 7beta-HSDH in a double enzyme system, where the couple formate/formate dehydrogenase allows the cofactor recycle, affords 6alpha-fluoro-3alpha, 7beta-dihydroxy-5beta-cholan-24-oic acid (6-FUDCA) by reduction of the corresponding 7-keto derivative. This compound is not obtainable by microbiological route. The efficient and mild hydrolysis of glycinates and taurinates of bile acids with CGH is also reported. Very promising results are also obtained with bile acid containing raw materials.

Cross-Metathesis of C-Allyl Iminosugars with Alkenyl Oxazolidines as a Key Step in the Synthesis of C-Iminoglycosyl α-Amino Acids.1 A Route to Iminosugar Containing C-Glycopeptides

[structures: see text] A general access to a novel class of sugar alpha-amino acids composed of iminofuranose and iminopyranose residues anomerically linked to the glycinyl group through an alkyl chain is described. A set of eight compounds was prepared by the same reaction sequence involving as an initial step the Grubbs Ru-carbene-catalyzed cross-metathesis (CM) of various N-Cbz-protected allyl C-iminoglycosides with N-Boc-vinyl- and N-Boc-allyloxazolidine. The isolated yields of the CM products (mixtures of E- and Z-alkenes) varied in the range 40-70%. Each mixture was elaborated by first reducing the carbon-carbon double bond using in situ generated diimide and then unveiling the N-Boc glycinyl group [CH(BocNH)CO2H] by oxidative cleavage of the oxazolidine ring by the Jones reagent. All amino acids were characterized as their methyl esters. The insertion of a model C-iminoglycosyl-2-aminopentanoic acid into a tripeptide via sequential carboxylic and amino group coupling with L-phenylalanine derivatives was carried out as a demonstration of the potential of these sugar amino acids in designed glycopeptide synthesis.

Assembling Heterocycle-Tethered C-Glycosyl and α-Amino Acid Residues via 1,3-Dipolar Cycloaddition Reactions

The 1,3-dipolar cycloadditions of C-glycosyl nitrile oxides and acetylenes to an alkyne and an azide, respectively, bearing a masked glycinyl moiety furnished disubstituted isoxazoles and triazoles. Unveiling the glycinyl group in these cycloadducts afforded C-glycosyl alpha-amino acids in which the two bioactive entities were tethered through rigid five-membered heterocycles. Optimized entries to the same compounds involved the use of unmasked but protected alkyne- and azide-containing amino acids as the partners of 1,3-dipolar cycloadditions.

New synthesis of pyrrolidine homoazasugars via aminohomologation of furanoses and their use for the stereoselective synthesis of aza-C-disaccharides

The introduction of a formyl group at the anomeric center of 2,3,5-tri-O-benzyl furanoses and substitution of the ring oxygen with a basic nitrogen atom (aminohomologation) was carried out via stereoselective addition of 2-lithiothiazole to N-benzyl, N-furanosylhydroxylamines (masked N-benzyl sugar nitrones), followed by reductive dehydroxylation of the resulting open-chain adducts, and then ring closure via intramolecular displacement of the free hydroxy group by the amino group and unmasking of the formyl group from the thiazole ring. The resulting formyl aza-C-glycosides were transformed into 2,5-dideoxy-2,5-imino-hexitols (pyrrolidine homoazasugars) by reduction of the formyl to the hydroxymethyl group and removal of the O- and N-benzyl groups by hydrogenolysis. This reaction sequence was applied to four furanoses (D-arabino, D-ribo, D-lyxo, L-xylo) to give the hydroxy- and amino-free homoazasugars, including the natural product 2,5-dideoxy-2,5-imino-D-mannitol, in 17% overall yields (six steps). The formyl aza-C-glycosides proved to be valuable intermediates for the synthesis of more complex derivatives. In fact, these sugar aldehydes were employed in Wittig-type coupling reactions with galactose and ribose phosphoranes to give bis-glycosylated alkenes, which upon reduction of the double bond were transformed into methylene isosteres of (1-->6)- and (1-->5)-linked disaccharides in which one of the two sugar moieties was an azasugar (aza-(1-->x)-C-disaccharides).