The influence of cosolvent concentration on enzymatic kinetic resolution of <i>trans</i>-2-phenyl-cyclopropane-1-carboxylic acid derivatives

<p>A method to improve the enantioselectivity of lipase-catalyzed kinetic resolution (KR) of <i>trans</i>-2-phenyl-cyclopropane-1-carboxylic acid derivatives in water–acetone solution is presented. Two different approaches were compared: enzyme-catalyzed esterification and enzymatic hydrolysis of the target ester. A substantial influence of enzyme type, ethoxy group donor, and solvent on conversion and enantioselectivity of the enzymatic esterification was noted. While enzymatic esterification proceeds with poor enantioselectivity, the hydrolysis of target ester proceeds efficiently. Studies on the influence of cosolvent used for the enzymatic hydrolysis reaction showed that kinetic resolution can be performed in acetone and water buffer mixture predominantly containing organic solvent. Any change in organic solvent content resulted in a substantial decrease in enantioselectivity from almost <i>E</i> = 150 to less than 5.</p

Studies on the Synthesis of Endocyclic Enol Lactones via a RCM of Selected Vinyl Esters

The novel and efficient approach toward the synthesis of endocyclic enol lactones was devised based on ring-closing metathesis of unsaturated carboxylic acids vinyl esters. Systematic studies revealed that vinyl esters are suitable substrates for RCM reaction. The developed methodology offers an easy route for synthetically challenging target molecules with different functional groups and substitution. We have also demonstrated that vinyl esters of cyclic carboxylic acids can be successfully applied for domino ring-opening ring-closing metathesis sequences

Dynamics of Intramolecular Excited State Proton Transfer in Emission Tunable, Highly Luminescent Imidazole Derivatives

The enol–keto excited state dynamics of a series of emission tunable imidazole derivatives undergoing excited state intramolecular proton transfer (ESIPT) were determined by means of steady state and time-resolved spectroscopic techniques in different solvents at room temperature and at 77 K. Examination of the corresponding non-ESIPT compounds, with the proton transfer function deliberately blocked, was carried out for comparison. At room temperature, the ESIPT process in the examined samples, determined by picosecond streak camera experiments, had lifetimes ranging from less than 10 ps to ca. 100 ps, and the resulting keto forms deactivated with lifetimes less than 100 ps up to a few nanoseconds. Delayed luminescence detection at 77 K in solid glasses allowed the identification of the phosphorescence of the enolic form and, in a few cases, P-type delayed fluorescence was also seen. The phosphorescence lifetimes were in the range of seconds at 77 K. The enolic triplet excited state absorption at RT, determined by nanosecond laser flash-photolysis, displayed a maximum around 460–500 nm and lifetimes on the order of tens of microseconds. In a few cases, a broad band with a maximum around 420 nm was detected and tentatively ascribed to the triplet excited state of the keto form. Reaction rates with oxygen on the order of (2–4) × 10⁹ M^–1 s^–1 were measured

Regioselective Enzymatic Carboxylation of Phenols and Hydroxystyrene Derivatives

The enzymatic carboxylation of phenol and styrene derivatives using (de)carboxylases in carbonate buffer proceeded in a highly regioselective fashion: Benzoic acid (de)carboxylases selectively formed <i>o</i>-hydroxybenzoic acid derivatives, phenolic acid (de)carboxylases selectively acted at the β-carbon atom of styrenes forming (<i>E</i>)-cinnamic acids

Electrochemically Driven Intramolecular Oxidative Aromatic Coupling as a Pathway toward π‑Extended Porphyrins

A Ni­(II) complex of a π-extended porphyrin bearing three mesityl substituents and one electron-rich naphthalene moiety has been prepared via electrochemical oxidation. It was proven that the whole oxidative process starts from electrochemical generation of a radical-cation on the porphyrin core. Electrochemistry and spectroelectrochemistry of both a naphthalenyl-substituted porphyrin and a porphyrin with a fused naphthalenyl group on the π-ring system provide clear distinction between metal- and ring-centered processes. The redox reactivity of the naphthalenyl-substituted metalloporphyrin in nonaqueous media is presented while outlining the most important structural factors which influence the reversible half-wave potentials for oxidation and reduction of this complex and the following chemical reactions which lead to an extended π-system