Isoxazole group directed Rh(III)-catalyzed alkynylation using TIPS-EBX.

A highly effective isoxazole directed ortho C-H alkynylation has been developed. Rhodium(III) catalyzed direct di-(and/or mono) alkynylation using a hypervalent iodine reagent (TIPS-EBX) is reported. The reaction proceeds with a wide substrate scope under benign conditions. Preliminary mechanistic studies support this chelation assisted C-H alkynylation.

Intramolecular Hydroarylation of Arenes via Imidazole-Directed C-H Activation in Aqueous Methanol Using Rhodium(III) as the Catalyst and Mechanistic Study.

A mild and greener approach for intramolecular regioselective hydroarylation is described for the efficient and elegant preparation of a number of dihydrobenzofurans and dihydrobenzo[b]thiophenes using imidazole as a directing group and Rh(III) as a catalyst. Moreover, the protocol may be extended to the formation of indoline and chromane derivatives. Deuterium scrambling experiments and characterization of isolated rhodacycle intermediate were explored to understand the mechanism in a better way.

Partial purification and characterization of a thermophilic and alkali-stable laccase of Phoma herbarum isolate KU4 with dye-decolorization efficiency.

Production of an extracellular thermophilic and alkali stable laccase from Phoma herbarum isolate KU4 was reported for the first time, both in submerged fermentation (SmF, highest 1590 U/mL) and solid state fermentation (SSF, highest 2014.21 U/mL) using agro-industrial residues. The laccase was partially purified to 7.93 fold with the apparent molecular weight of 298 kDa. The enzyme had pH optimum at 5.0 and temperature optimum at 50 °C, with maximum stability at pH 8.0. It showed activity towards various phenolic and non-phenolic compounds. The kinetic parameters, Km, Vmax and Kcat of the laccase for DMP were 0.216 mM, 270.27 U/mg and 506.69 s-1, respectively. Laccase activity was inhibited by various metal ions and conventional inhibitors, however, it was slightly increased by Zn2+. The laccase showed good decolorization efficiency towards four industrial dyes, namely, methyl violet (75.66%), methyl green (65%), indigo carmine (58%) and neutral red (42%) within 24 h. FTIR analysis of the decolorized products confirmed the degradation of the dyes. The decolorization efficiency of the enzyme suggests that the partially purified laccase could be used to decolorize synthetic dyes present in industrial effluents and for waste water treatments. The thermophilic and alkali stable laccase may also have wider potential industrial applications.

Additive-Free, Pd-Catalyzed 3-Amino-1-methyl-1H-pyridin-2-one-Directed C(sp2)-H Arylation and Methylation in Water.

Small molecules containing a 2-pyridone unit received much attention due to their significance in medicinal chemistry. In this regard, development of novel methodologies via metal-catalyzed carbon-carbon bond formation by chelation-assisted C-H activation will be an attractive method to achieve therapeutically important 2-pyridone analogues and arylated acid synthons. We report our studies on a Pd(II)-catalyzed coupling reaction between methyl, aryl, heteroaryl iodides, and sp2 carbons both at ß- and γ-positions using 3-amino-1-methyl-1H-pyridin-2-one as an efficient, built-in bidentate N,O-directing group (DG) toward the synthesis of pyridone derivatives. The effect of temperature, solvent, reagent equivalence, and substrate has been investigated for this DG-mediated late-stage functionalization reactions along with the crystal structure of a selected analogue. Moreover, this DG has been successfully applied for ortho-selective C(sp2)-H activation in aqueous medium in high yields to demonstrate the practicability of this present methodology.

Chemoenzymatic reduction of citreorosein and its implications on aloe-emodin and rugulosin C (bio)synthesis.

A chemoenzymatic reduction of citreorosein by the NADPH-dependent polyhydroxyanthracene reductase from Cochliobolus lunatus or MdpC from Aspergillus nidulans in the presence of Na2S2O4 gave access to putative biosynthetic intermediates, (R)-3,8,9,10-tetrahydroxy-6-(hydroxymethyl)-3,4-dihydroanthracene-1(2H)-one and its oxidized form, (R)-3,4-dihydrocitreorosein. Herein, we discuss the implications of these results towards the (bio)synthesis of aloe-emodin and (+)-rugulosin C in fungi.

Stereoselective Peptide Modifications via ß-C(sp3)-H Arylations.

Palladium-catalyzed stereoselective ß-arylations of phenylalanine, proline- and pipecolinic acid-containing peptides are a versatile tool for peptide modifications. The reactions proceed without epimerization of stereogenic centers in the peptide chain. If suitable functionalized aryl iodides are introduced, subsequent cross coupling reactions can be used for further modifications. The 8-amino quinoline (AQ) directing group can easily be removed, allowing the prolongation of the peptide chain at the C-terminus.

Pd(OAc)2-catalyzed dehydrogenative C-H activation: An expedient synthesis of uracil-annulated ß-carbolinones.

An intramolecular dehydrogenative C-H activation enabled an efficient synthesis of an uracil-annulated ß-carbolinone ring system. The reaction is simple, efficient and high yielding (85-92%).

Advances in metal-free heterocycle-based columnar liquid crystals.

Liquid crystals are ordered soft materials formed by self-organized molecules and can potentially be used as new functional materials for electron-, ion- or molecular-transport; optical; and bio-active materials. In particular, the columnar liquid crystals are promising candidates used in various optical and electronic devices. For this purpose, design and synthesis of unconventional materials are essential. In this review, we have summarized several approaches for the synthesis of columnar liquid crystals composed of various heterocyclic systems. We also outline their liquid crystalline and other relevant properties, and their suitability for applications in diverse fields.

An iron(ii)-based metalloradical system for intramolecular amination of C(sp2)-H and C(sp3)-H bonds: synthetic applications and mechanistic studies.

A catalytic system for intramolecular C(sp2)-H and C(sp3)-H amination of substituted tetrazolopyridines has been successfully developed. The amination reactions are developed using an iron-porphyrin based catalytic system. It has been demonstrated that the same iron-porphyrin based catalytic system efficiently activates both the C(sp2)-H and C(sp3)-H bonds of the tetrazole as well as azide-featuring substrates with a high level of regioselectivity. The method exhibited an excellent functional group tolerance. The method affords three different classes of high-value N-heterocyclic scaffolds. A number of important late-stage C-H aminations have been performed to access important classes of molecules. Detailed studies (experimental and computational) showed that both the C(sp2)-H and C(sp3)-H amination reactions involve a metalloradical activation mechanism, which is different from the previously reported electro-cyclization mechanism. Collectively, this study reports the discovery of a new class of metalloradical activation modes using a base metal catalyst that should find wide application in the context of medicinal chemistry, drug discovery and industrial applications.