Intramolecular addition of carbon radicals to aldehydes: synthesis of enantiopure tetrahydrofuran-3-ols

Origin of the Unexpected Enantioselectivity in the Enzymatic Reductions of 5-Membered-Ring Heterocyclic Ketones Catalyzed by Candida parapsilosis Carbonyl Reductases

Candida parapsilosis carbonyl reductases (CpRCR) have been widely used for the reductive conversion of ketone precursors and chiral alcohol products in pharmaceutical industries. The enzymatic enantioselectivity is believed to be related to the shape complementation between the cavities in the enzymes and the substitutions of the ketone substrates. In this work, we reported an unexpected enantioselectivity in the enzyme reductions of dihydrofuran-3(2H)-one (DHF) to (S)-tetrahydrofuran-3-ol (DHF-ol, enantiomeric excess: 96.4%), while dihydrothiophen-3(2H)-one substrate (DHT) was unproductive under the same experimental conditions. To rationalize the exclusive S-configuration and the specific reactivity of DHF, we carried out molecular dynamics simulations for the reacting complexations of DHF with CpRCR, and DHT with CpRCR. Our calculations indicate that DHF preferentially binds to the small cavity near L119, F285, and W286, while the large cavity near the α1 helix was mainly occupied by solvent water molecules. Moreover, the pre-reaction state analysis suggests that the pro-S conformations were more abundant than the pro-R, in particular for DHF. This suggests that the non-polar interaction of substrate C4-C5 methylene contacting the hydrophobic side-chains of L119-F285-W286, and the polar interaction of funanyl oxygen exposing the solvent environment play important roles in the enantioselectivity and reactivity. The phylogenetic tree of CpRCR homologues implies that a variety of amino acid combinations at positions 285 and 286 were available and thereby potentially useful for redesigning enantioselective reductions of 5-membered-ring heterocyclic ketones.

Efficient Protocol for Synthesis of β-Hydroxy(alkoxy)selenides via Electrochemical Iodide-Catalyzed Oxyselenation of Styrene Derivatives with Dialkyl(aryl)diselenides

An efficient protocol for the synthesis of β-hydroxy(alkoxy)selenides was developed through the electrochemical iodide-catalyzed oxyselenation of styrene derivatives with dialkyl(aryl)diselenides under mild reaction conditions. Mechanistic studies showed that the cation I+ is involved during the whole process, and accelerates the formation of seleniranium ion via substitution and addition reaction with dialkyl(aryl)diselenides and styrene derivatives. The corresponding products are formed in good to excellent yields. This electrochemical oxyselenation provides an efficient strategy for difunctionalization of alkenes.

Strategy for Overcoming Full Reversibility of Intermolecular Radical Addition to Aldehydes: Tandem C-H and C-O Bonds Cleaving Cyclization of (Phenoxymethyl)arenes with Carbonyls to Benzofurans

An intermolecular addition of carbon radicals enabled by a cascade radical coupling strategy is developed. It includes an intermolecular alkyl radical addition to a carbonyl group followed by an intramolecular alkoxy radical addition to haloarenes and produces substituted benzofurans in high yields. The radical nature of this reaction is explored by radical trapping experiments and EPR analysis. The mechanism is investigated by KIE experiments and control experiments. This method could provide rapid and practical access to the key intermediate of TAM-16, a safe and potent antibacterial agent for treating tuberculosis, and, therefore, is of great importance for organic synthesis and the pharmaceutical industry.

Synthesis of Novel Selenides Bearing Benzenesulfonamide Moieties as Carbonic Anhydrase I, II, IV, VII, and IX Inhibitors

A series of novel selenides bearing benzenesulfonamide moieties was synthesized and investigated for the inhibition of five human (h) isoforms of zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), hCA I, II, IV, VII, and IX. These enzymes are involved in a variety of diseases, including glaucoma, retinitis pigmentosa, epilepsy, arthritis, and tumors. The investigated compounds showed potent inhibitory action against hCA II, VII, and IX, in the low nanomolar range, thus making them of interest for the development of isoform-selective inhibitors and as candidates for biomedical applications.

Copper-catalyzed cascade annulation of unsaturated α-bromocarbonyls with enynals: a facile access to ketones from aldehydes

A Cu-catalyzed cascade annulation of enynals with alkenyl or alkynyl α-bromocarbonyls for the synthesis of various cyclohexenone-fused polycyclic compounds is described. Up to six new C-C bonds and four new carbocycles can be established in a single reaction, highlighting the high efficiency and step-economics of this protocol. This reaction offers a novel and straightforward entry to the synthesis of ketones featuring the addition of carbon radicals to aldehydes.