Insights into E.†coli Cyclopropane Fatty Acid Synthase (CFAS) Towards Enantioselective Carbene Free Biocatalytic Cyclopropanation.

Cyclopropane fatty acid synthases (CFAS) are a class of S-adenosylmethionine (SAM) dependent methyltransferase enzymes able to catalyse the cyclopropanation of unsaturated phospholipids. Since CFAS enzymes employ SAM as a methylene source to cyclopropanate alkene substrates, they have the potential to be mild and more sustainable biocatalysts for cyclopropanation transformations than current carbene-based approaches. This work describes the characterisation of E. coli CFAS (ecCFAS) and its exploitation in the stereoselective biocatalytic synthesis of cyclopropyl lipids. ecCFAS was found to convert phosphatidylglycerol (PG) to methyl dihydrosterculate 1 with up to 58 % conversion and 73 % ee and the absolute configuration (9S,10R) was established. Substrate tolerance of ecCFAS was found to be correlated with the electronic properties of phospholipid headgroups and for the first time ecCFAS was found to catalyse cyclopropanation of both phospholipid chains to form dicyclopropanated products. In addition, mutagenesis and in silico experiments were carried out to identify the enzyme residues with key roles in catalysis and to provide structural insights into the lipid substrate preference of ecCFAS. Finally, the biocatalytic synthesis of methyl dihydrosterculate 1 and its deuterated analogue was also accomplished combining recombinant ecCFAS with the SAM regenerating AtHMT enzyme in the presence of CH3I and CD3I respectively.

Discovery and Rational Mutagenesis of Methionine Sulfoxide Reductase Biocatalysts To Expand the Substrate Scope of the Kinetic Resolution of Chiral Sulfoxides.

Methionine sulfoxide reductase A (MsrA) enzymes have recently found applications as nonoxidative biocatalysts in the enantioselective kinetic resolution of racemic sulfoxides. This work describes the identification of selective and robust MsrA biocatalysts able to catalyze the enantioselective reduction of a variety of aromatic and aliphatic chiral sulfoxides at 8-64 mM concentration with high yields and excellent ees (up to 99%). Moreover, with the aim to expand the substrate scope of MsrA biocatalysts, a library of mutant enzymes has been designed via rational mutagenesis utilizing in silico docking, molecular dynamics, and structural nuclear magnetic resonance (NMR) studies. The mutant enzyme MsrA33 was found to catalyze the kinetic resolution of bulky sulfoxide substrates bearing non-methyl substituents on the sulfur atom with ees up to 99%, overcoming a significant limitation of the currently available MsrA biocatalysts.

Antioxidant activity of some lichen metabolites.

Antioxidant activity of several classes of lichen metabolites were assessed in the in vitro superoxide radical (SOR), nitric oxide radical and 2,2-diphenyl-1-picrylhydrazil radical scavenging assays. The despsides sekikaic acid and lecanoric acid showed promising antioxidant activity in SOR assay with IC50 values of 82.0 ± 0.3 µmol and 91.5 ± 2.1 µmol, respectively, while the depsidone lobaric acid exhibited an IC50 value of 97.9 ± 1.6 µmol, all relative to the standard, propyl gallate (IC50 = 106.0 ± 1.7 µmol). One of the most abundant mononuclear phenolic compounds, methyl-ß-orcinol carboxylate was found to be a potent NO scavenger (IC50 = 84.7 ± 0.1 µmol), compared to the standard rutin (IC50 = 86.8 ± 1.9 µmol).

Essential oil compositions and antioxidant properties of the roots of twelve Anatolian Paeonia taxa with special reference to chromosome counts.

Essential oil compositions and antioxidant potentials of fourteen ethanol (75%) root extracts prepared from twelve taxa of the genus Paeonia (Paeoniaceae), including P. arietina Anders., P. daurica Andrews, P. xkayae N. Ozhatay, P. kesrouanensis Thiéb., P. mascula (L.) Miller subsp. arasicola G. Kaynak, ö. Yilmaz & R. Daskin, P. mascula (L.) Miller subsp. bodurii N. Ozhatay, P. cf. mascula L. (Mill.) subsp. mascula (two samples from central and northeastern Anatolia), P. cf. officinalis Retz., P. peregrina Miller (two samples from western and northwestern Anatolia), P. tenuifolia L., P. turcica Davis & Cullen, and P. wittmanniana Hartwiss ex Lindl. were assessed. The chromosome numbers of the root tips of the species were examined using chromosome staining technique with Shiff's reagent under Leitz microscope. The essential oils of the roots of the Paeonia species were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) and the major components were identified as salicylaldehyde (10%-94.4%), cis-myrtanal (5.5%-59.7%), and methyl salicylate (2%-52.2%). Antioxidant potentials were tested against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and nitric oxide (NO) radicals using propyl gallate and rutin as the references. Total phenolic contents of the ethanol extracts were determined using Folin-Ciocalteau's method. The extracts exerted moderate NO scavenger effect and displayed insignificant DPPH radical scavenger activity at 500 microg mL(-1). On the other hand, P. daurica, P. tenuifolia and P. cf. mascula subsp. mascula are diploids with 2n = 10, while other nine taxa are tetraploids with 2n = 20.

Metathesis Cascade Strategies (ROM-RCM-CM): A DOS approach to Skeletally Diverse Sultams.

The development of a ring-opening metathesis/ring-closing metathesis/cross metathesis (ROM-RCM-CM) cascade strategy to the synthesis of a diverse collection of bi- and tricyclic sultams is reported. In this study, functionalized sultam scaffolds derived from intramolecular Diels-Alder (IMDA) reactions undergo metathesis cascades to yield a collection tricyclic sultams. Additional appendage based diversity was achieved by utilizing a variety of CM partners.

High-load, oligomeric dichlorotriazine: a versatile ROMP-derived reagent and scavenger.

A new high-load, soluble oligomeric dichlorotriazine (ODCT) reagent derived from ring-opening metathesis polymerization (ROMP) is reported as an effective coupling reagent, scavenger of nucleophilic species, and activator of DMSO for the classic Swern oxidations. Two variants of this reagent (2G)ODCT 4 and (1G)ODCT 16, possessing theoretical loads of 5.3 and 7.3 mmol/g, respectively, have been synthesized. Preparation was accomplished via simple synthetic protocols affording free flowing powders, amenable for large-scale production. Removal of the spent oligomeric reagent was achieved via either precipitation of the spent reagent or simple filtration utilizing a silica SPE, followed by solvent removal, to deliver products in excellent yield and purity. In addition, the corresponding norbornenyl monomer 3 was successfully demonstrated in a couple-ROMP-filter protocol utilizing in situ polymerization, achieving comparable results versus the corresponding oligomeric variant.