Asymmetric synthesis of 2-substituted 4-chromanones using enzyme-catalyzed reactions

Polyketides From the Endophytic Fungus Cladosporium sp. Isolated From the Mangrove Plant Excoecaria agallocha

Five new polyketides (2–6) and ten known compounds (1 and 7–15) were obtained from the fermentation products of the endophytic fungus Cladosporium sp. OUCMDZ-302 with the mangrove plant, Excoecaria agallocha (Euphorbiaceae). The new structures of 2–6 were established on the basis of ECD, specific rotation and spectroscopic data as well as the chemical calculation. Compound 7 showed cytotoxicity against H1975 cell line with an IC₅₀ value of 10.0 μM. Compounds 4 and 8–10 showed radical scavenging activity against DPPH with the IC₅₀ values of 2.65, 0.24, 5.66, and 6.67 μM, respectively. In addition, the absolute configuration of compound 1 was solidly determined by X-ray and sugar analysis of the acidic hydrolysates for the first time as well as those of compounds 8–10 in this paper.

Nickel-promoted highly regioselective carboxylation of aryl ynol ether and its application to the synthesis of chiral β-aryloxypropionic acid derivatives

Nickel(0)-promoted carboxylation of aryl ynol ether proceeded in a highly regioselective manner to produce α-substituted-β-aryloxyacrylic acid derivatives. The α-substituted-β-aryloxyacrylic acids were transformed into the corresponding β-aryloxypropionic acid derivative as an optically active form via rhodium-catalyzed asymmetric hydrogenation.

An eco-friendly enantioselective access to (R)-naringenin as inhibitor of proinflammatory cytokine release

(RS)-Naringenin is a flavanone well-known for its beneficial health-related properties, such as its anti-inflammatory activity. The preparative enantioselective chromatographic resolution of commercial (RS)-naringenin was performed on a Chiralpak AD-H column (500×50 mm i.d., dp 20 μm) using MeOH as eluent. The developed method is in accordance with the principles of green chemistry, since the environmental impact was lowered by recycling of the eluent, and allowed the production of gram amounts of each enantiomer with high purity (chemical purity >99%, enantiomeric excess (ee) >94%). Racemic and enantiomeric naringenin were subjected to an exhaustive in vitro investigation of anti-inflammatory activity, aimed at evaluating the relevance of chirality. The assay with cultured human peripheral blood mononuclear cells (hPBMC) activated by phytohemagglutinin A revealed that (R)-naringenin was more effective in inhibiting T-cell proliferation than the (S)-enantiomer and the racemate. Moreover, (R)-naringenin significantly reduced proinflammatory cytokine levels such as those of TNF-α and, with less potency, IL-6. These results evidenced the anti-inflammatory potential of naringenin and the higher capacity of (R)-naringenin to inhibit both in vitro hPBMC proliferation and cytokine secretion at non toxic doses. Thus, (R)-naringenin is a promising candidate for in vivo investigation.

Nanobio interfaces: charge control of enzyme/inorganic interfaces for advanced biocatalysis

Specific approaches to the rational design of nanobio interfaces for enzyme and protein binding to nanomaterials are vital for engineering advanced, functional nanobiomaterials for biocatalysis, sensing, and biomedical applications. This feature article presents an overview of our recent discoveries on structural, functional, and mechanistic details of how enzymes interact with inorganic nanomaterials and how they can be controlled in a systematic manner using α-Zr(IV)phosphate (α-ZrP) as a model system. The interactions of a number of enzymes having a wide array of surface charges, sizes, and functional groups are investigated. Interactions are carefully controlled to screen unfavorable repulsions and enhance favorable interactions for high affinity, structure retention, and activity preservation. In specific cases, catalytic activities and substrate selectivities are improved over those of the pristine enzymes, and two examples of high activity near the boiling point of water have been demonstrated. Isothermal titration calorimetric studies indicated that enzyme binding is coupled to ion sequestration or release to or from the nanobio interface, and binding is controlled in a rational manner. We learned that (1) bound enzyme stabilities are improved by lowering the entropy of the denatured state; (2) maximal loadings are obtained by matching charge footprints of the enzyme and the nanomaterial surface; (3) binding affinities are improved by ion sequestration at the nanobio interface; and (4) maximal enzyme structure retention is obtained by biophilizing the nanobio interface with protein glues. The chemical and physical manipulations of the nanobio interface are significant not only for understanding the complex behaviors of enzymes at biological interfaces but also for desiging better functional nanobiomaterials for a wide variety of practical applications.

A practical access to highly enantiomerically pure flavanones by catalytic asymmetric transfer hydrogenation

A surprisingly selective, non-enzymatic kinetic resolution of readily available, racemic β-chiral ketones enabled the title process, which was applied to a rapid synthesis of several bioactive flavanones in virtually enantiopure form (see scheme; MOM=methoxymethyl, Ts=p-toluenesulfonyl).