Identification and Structure Analysis of an Unusual Halohydrin Dehalogenase for Highly Chemo-, Regio- and Enantioselective Bio-Nitration of Epoxides.

We report the discovery of an unusual halohydrin dehalogenase, HHDHamb, that can work under relatively low acidic conditions and extremely low temperatures for the bio-nitration of epoxides using nitrite as a nitrating agent. The bio-nitration strategy exhibits high chemo-, regio-, and enantioselectivity, catalyzing the kinetic resolution of various epoxides to enantiopure ß-nitroalcohols with nitro-bearing stereocenters in up to 41 % isolated yield and >99 % enantiomeric excess (ee). Additionally, the bio-nitration method displays a high reaction efficiency and can be performed on a gram scale. We also solved the crystal structure of HHDHamb to understand the possible structural determinants of chemoselectivity control in the bio-nitration reaction.

Biocatalytic Thionation of Epoxides for Enantioselective Synthesis of Thiiranes.

Expanding the enzymatic toolbox for the green synthesis of valuable molecules is still of high interest in synthetic chemistry and the pharmaceutical industry. Chiral thiiranes are valuable sulfur-containing heterocyclic compounds, but relevant methods for their enantioselective synthesis are limited. Herein, we report a biocatalytic thionation strategy for the enantioselective synthesis of thiiranes, which was developed based on the halohydrin dehalogenase (HHDH)-catalyzed enantioselective ring-opening reaction of epoxides with thiocyanate and a subsequent nonenzymatic rearrangement process. A novel HHDH was identified and engineered for enantioselective biocatalytic thionation of various aryl- and alkyl-substituted epoxides on a preparative scale, affording the corresponding thiiranes in up to 43 % isolated yield and 98 % ee. Large-scale synthesis and useful transformations of chiral thiiranes were also performed to demonstrate the utility and scalability of the biocatalytic thionation strategy.

The antioxidant activities of flavonoids in Jerusalem artichoke (Helianthus tuberosus L.) leaves and their quantitative analysis.

The main targets of this work were to evaluate the antioxidative properties of flavonoids in Jerusalem artichoke (Helianthus tuberosus L.) leaves and quantitatively determine their contents. 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis (3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) and hydroxyl free radicals scavenging assays were performed to determine their antioxidative capacities. The validated ultra high-performance liquid chromatography-quadrupole-time-of-flight/mass spectrometry (UHPLC-Q-TOF/MS) method was subsequently applied to the quality evaluation of eleven batches of Jerusalem artichoke leaves grown in different habitats at different harvesting time. Results indicated that two flavonoids isolated from Jerusalem artichoke leaves showed stronger antioxidant effects than the positive control, butylated hydroxytoluene (BHT). And the total contents of the two flavonoids in the Jerusalem artichoke leaves of flowering stage from Dalian, Liaoning Province, China, were the highest, their contents varied significantly depending on region and harvesting time. This study indicated that the leaves of Jerusalem artichoke possessed excellent antioxidant properties, highlighting their candidacy as natural antioxidants, which could be utilized therapeutically to protect the body from diseases caused by oxidative stress.