Stable silylenes.

M Haaf; T A Schmedake; R West

doi:10.1021/ar950192g

Home/Archive/PubMed

PubMed · 11041835

Stable silylenes.

M Haaf·T A Schmedake·R West

View original source ↗Export metadata ↓

Abstract

The field of stable silylene research has grown dramatically since the first isolation of a stable silylene in 1994. Prior to 1994, silylenes existed only as reactive intermediates, isolable only in low-temperature matrixes. Since then, several stable silylenes have been synthesized, some in fact showing remarkable thermal stability. This Account highlights the developments in stable silylene chemistry, including theoretical and experimental studies attempting to explain the remarkable stability of the silylenes as well as the rapidly expanding reaction chemistry of the stable silylenes.

Explore related subjects

Molecular Structure Silicon Compounds Spectrum Analysis Journal Article Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

M Haaf, T A Schmedake, R West. 2000. Stable silylenes.. https://doi.org/10.1021/ar950192g

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2025

Biosynthesis of the 5-Isoxazolidinone-Containing Hexacyclic Structure of Parnafungin.

Parnafungins A-D (1-4) are fungal natural products that inhibit eukaryotic poly(A)-polymerase and were first discovered by Merck & Co., Inc., through a Candida albicans Fitness Test (CaFT) screening program. The biological activity of parnafungins is a result of the unique fused hexacyclic structure highlighted by a 5-isoxazolidinone (5ILD) N-heterocycle. In this work, we characterize the complete biosynthetic pathway of parnafungins through heterologous reconstitution and enzymatic assays. Nearly half of the 26-gene biosynthetic gene cluster of parnafungin is responsible for the production of a known polyketide natural product, blennolide C. Starting from the blennolide C fragment, a three-enzyme cascade involving CoA-ligase ParJ, P450 ParO, and DUF829 ParD catalyzes the formal biaryl cross-coupling between blennolide C and anthranilate. Subsequent oxidative cyclization generates a phenanthridine product that is then reduced by atypical short-chain reductase ParT. N-Hydroxylation by flavin-dependent monooxygenase ParB and subsequent lactonization catalyzed by a homologue of dienenolactone hydrolase ParF form the 5ILD ring and complete the biosynthesis of 1 and 2. Methylation of 1 forms parnafungin C (3), and lastly epoxidation forms parnafungin D (4). Together, our work revealed the chemical logic and enzymology in extending the biosynthetic pathway of a well-characterized natural product, blennolide C, to introduce considerable additional structural diversity that affords parnafungins with unique biological activity.

Molecular Structure↗

PubMed2007

Positive and negative ion electrospray tandem mass spectrometry (ESI MS/MS) of Boc-protected peptides containing repeats of L-Ala-gamma4Caa/gamma4Caa-L-Ala: differentiation of some positional isomeric peptides.

High-resolution electrospray ionization (ESI) quadrupole time-of-flight and ion trap tandem mass spectrometry has been used to distinguish the positional isomers of a new class of N-blocked hybrid peptides containing repeats of the amino acids, L-Ala-gamma(4)Caa ((l))/gamma(4)Caa((l))-L-Ala [Caa((l)) = Carbo (lyxose) amino acid, derived from D-mannose]. Both MS/MS and MS(3) of protonated isomeric peptides produce characteristic fragmentation involving the peptide backbone, Boc-group, and the side-chain. It is interesting to observe that the abundant y(n)(+) ions are formed when the corresponding amide -NH does not participate in the helical structures in solution phase and relatively low abundance y(n)(+) ions resulted when the amide -NH involves in the H-bonding. Thus, it was possible to identify the amide -NH hydrogens that participate in the helical structures through H-bonding in solution phase. Further, negative ion ESI MS/MS has also been found to be useful for differentiating these isomeric peptide acids.

Molecular Structure↗

PubMed2007

Two methods for the determination of enantiomeric excess and concentration of a chiral sample with a single spectroscopic measurement.

The previously established enantioselective indicator-displacement assays (eIDAs) for the determination of concentration and enantiomeric excess (ee) require two spectroscopic measurements for each chiral sample. To further simplify the operation of eIDAs, we now introduce two innovative analytical methods, both of which utilize a dual-chamber quartz cuvette, which reduces the number of spectroscopic measurements from two to one. An attractive feature of this cuvette is that the concentration- and ee-dependent absorption data can be collected at the isosbestic points or transparent regions of the spectra recorded in each individual chamber, thereby reflecting optical changes that occur in the other chamber. Therefore, two independent equations, which are needed to solve the values of the two independent variables-concentration and ee-can be established with only a single spectroscopic measurement. The first method takes advantage of this feature in conjunction with a judicious choice of indicator/host combinations to generate concentration- and ee-dependent calibration curves. Our second method removes the requirement to measure equilibrium constants and molar absorptivities altogether through the use of artificial neural networks (ANNs). The most frequently used three-layer feed-forward network is generated, which relates the absorption data to concentration and ee of the samples by training with a back propagation procedure. Here, the data collection is not limited to the isosbestic points or transparent regions. Both approaches enabled accurate and rapid determination of concentration and ee of chiral samples. The technology removes the relative difficulty, which is the need for two separate measurements for concentration and ee respectively, of analyzing chiral samples compared to achiral samples. When implemented in a high-throughput format, this technology should greatly facilitate the discovery of asymmetric catalysts in the same way as conventional high-throughput screening assays.

Molecular Structure↗