Synthesis of Si-Stereogenic Silanols by Catalytic Asymmetric Hydrolytic Oxidation.

Despite growing progress in the construction of chiral organosilicon compounds, the catalytic asymmetric synthesis of silicon-stereogenic silanols is less explored and remains a considerable challenge. Herein, we report the first enantioselective construction of silicon-stereogenic silanols by the catalytic asymmetric hydrolytic oxidation of dihydrosilanes. This practical procedure features ambient reaction conditions, high atom economy, good functional-group compatibility, and H2 as the only by-product, and produces a wide range of valuable chiral silanols and bis-silanols in decent yields with excellent chemo- and stereoselectivity.

Catalytic Asymmetric Synthesis of Silicon-Stereogenic Dihydrodibenzosilines: Silicon Central-to-Axial Chirality Relay.

A Rh-catalyzed asymmetric synthesis of silicon-stereogenic dihydrodibenzosilines featuring axially chiral 6-membered bridged biaryls is demonstrated. In the presence of a RhI catalyst with a chiral diphosphine ligand, a wide range of dihydrodibenzosilines containing both silicon-central and axial chiralities are conveniently constructed in excellent enantioselectivities via dehydrogenative C(sp3 )-H silylation. Absolute configuration analysis by single-crystal X-ray structures revealed a novel silicon central-to-axial chirality relay phenomenon, which we believe will inspire further research in the field of asymmetric catalysis and chiroptical materials.

Electrochemical Radical Silyl-Oxygenation of Activated Alkenes.

An efficient electrochemical radical silyl-oxygenation of electron-deficient alkenes is demonstrated, which gives access to a variety of new highly functionalized silicon-containing molecules, including ß-silyl-cyanohydrin derivatives in good yields with excellent chemo- and regio-selectivity. This electrochemical radical silylation process conducts under mild conditions without the use of transition metal catalyst or chemical oxidant and exhibits a wide scope of substrate silanes with high functional-group tolerance. The ability to access silyl radicals using electrochemical Si-H activation offers new perspectives for the synthesis of valuable organosilicon compounds in a sustainable and green manner.

Asymmetric Total Synthesis of the Highly Strained 4ß-Acetoxyprobotryane-9ß,15α-diol.

The first and asymmetric total synthesis of 4ß-acetoxyprobotryane-9ß,15α-diol, containing a rare and highly strained trans-fused bicyclo[3.3.0]octane ring system, has been achieved. The synthetically challenging [6-5-5] tricyclic ring system in the final product was efficiently and diastereoselectively synthesized via an asymmetric rhodium-catalyzed [4 + 2] cycloaddition reaction, followed by a unique benzilic acid type rearrangement under very mild conditions. The seven contiguous stereocenters were installed efficiently and diastereoselectively.

Field Monitoring and Analysis of the Vibration of Stay Cables under Typhoon Conditions.

Structural health monitoring systems provide many advantages for full-scale measurements in bridge monitoring. In this study, a strong landing typhoon event recorded at the Jintang Bridge (Zhejiang Province, China) in 2019 was selected to study the nonstationary wind and cable vibration characteristics. To study the characteristics of the recorded typhoon, the time-varying mean wind was extracted based on the adaptive method of the wavelet-matrix transform. The nonstationary characteristics of Typhoon Lekima, including the turbulence intensity, gust factor, and fluctuating wind power spectral density, were analyzed and compared with the stationary model characteristics of a typhoon, and the typical characteristics and parameters were obtained. In addition, the measured vibration response of the cables was analyzed. The vibration characteristics of the cables and the energy distribution of the wind speed wavelet packet were investigated. The vibrations at different positions were compared. A power spectrum analysis and a wavelet packet energy analysis of the cable were performed. The results of this study can be used as a basis for wind-resistant design and performance evaluation of bridges under similar operational conditions.

Asymmetric Total Synthesis of Bufospirostenin A.

The first and asymmetric total synthesis of bioactive bufospirostenin A, an unusual spirostanol with rearranged A/B rings, was accomplished. The synthetically challenging [5-7-6-5] tetracyclic ring system, found in bufospirostenin A and some other natural products, was efficiently constructed by the unique intramolecular rhodium-catalyzed Pauson-Khand reaction of an alkoxyallene-yne. The 11 stereocenters in the final product, including the 10 contiguous stereocenters, were installed diastereoselectively.

Pharmacokinetics of a novel nifedipine and pH-sensitive N-succinyl chitosan/alginate hydrogel bead in rabbits.

CONTEXT: A novel N-succinyl chitosan/alginate hydrogel bead was prepared by the ionic gelation method for controlled delivery of nifedipine (NF). OBJECTIVE: The delivery behavior of NF from the hydrogel bead was studied in rabbit body. MATERIALS AND METHODS: Nitrendipine was used as the internal standard and the concentration of NF in serum was determined by reversed-phase high-performance liquid chromatography. RESULTS: The assay was linear from 5 to 755 ng/mL. The limit of quantitation for NF was 5 ng/mL in serum, and the recovery was greater than 90%. The method was used to determine the concentration-time profiles of NF in the serum. The pharmacokinetic parameters were calculated by Drug and Statistics (ver 1.0) program. The mean Cmax was 320.2 ± 71.3 µg/L, the mean Tmax was 3.2 ± 0.5 hours, the mean t1/2 was 6.60 ± 2.17 hours, the mean AUC0-24 was 2.03 ± 0.25 mg h/L, the mean AUC0-∞ was 2.50 ± 0.36 mg h/L, the mean MRT0-24 was 8.57 ± 0.19 hours, and the mean MRT0-∞ was 15.2 ± 1.8 hours. DISCUSSION AND CONCLUSION: The pharmacokinetic characteristics were found by a two-compartment model following the oral administration of NF-loaded N-succinyl chitosan/alginate hydrogel beads in rabbits.