Reduction of xanthates by N-heterocyclic carbene boranes (NHC-boranes) has been suggested to occur a radical chain mechanism involving heretofore unknown NHC-boryl radicals. In support this suggestion, both the expected borane dithiocarbonate product and an unexpected xanthate have now isolated. These are first NHC-boranes with boron−sulfur bonds, their structures secured spectroscopic crystallographic means. The rate constants for H-atom transfer from NHC complex were determined using ring...

The placenta synthesizes insulin-like growth factors (IGFs) and their binding proteins (IGFBPs), which are believed to regulate its development in an autocrine/paracrine manner. To delineate the cellular sites of expression IGP IGFBP messenger ribonucleic acids (mRNAs) human throughout pregnancy, we used situ hybridization histochemistry with 35S-labeled IGF complementary RNA probes on placentas fetal membranes gestational ages 6 weeks term (40 weeks). In placental regions where trophoblasts...

Abstract

Cascade, domino, or tandem processes, that link together two more transformations in one pot, are increasing popularity because they lead to improvements synthetic efficiency and decreases environmental impact. Not only do these cascades contain choice mechanistic gems but also deliver compact elegant syntheses of complex natural products. Longer require functional groups precisely configured within carefully designed initial molecular architectures. Such "purposeful" molecules can be...

N-Heterocyclic carbene boranes (NHC-boranes) are a new "clean" class of reagents suitable for reductive radical chain transformations. Their structures well suited their reactivity to be tuned by inclusion different NHC ring units and appropriate placement diverse substituents. EPR spectra were obtained the boron-centered radicals generated on removal one BH(3) hydrogen atoms. This spectroscopic data, coupled with DFT computations, demonstrated that NHC-BH(2)* planar pi-delocalized species....

Using immunohistochemical techniques, we have determined the localization and distribution of CRH immunoreactivity (CRH-IR) in human placenta, fetal membranes, decidua, umbilical cord. Tissues were obtained at 6–8 weeks pregnancy, term, association with premature birth, from patients pregnancy-induced hypertension or diabetes mellitus. A polyclonal antibody to epithelial cell marker cytokeratin was used identify trophoblast cells. CRH-IR not detected placenta decidua gestation. In tissues...

Selective syntheses are now available for compounds of many classes, based on C-centered radicals, exploiting a diverse range mechanisms. The prospect chemistry around N- and O-centered radicals is probably more favorable because the importance heterocycles as biologically active materials. Heteroradical still comparatively underdeveloped due to need safe easy ways generating them. Oxime esters appeared promising candidates meet this literature reports our EPR spectroscopic examinations...

This research aimed to provide a new and "clean" synthetic method that would enable both known novel N-heterocycles be prepared efficiently. O-Phenyl oximes were found excellent precursors for iminyl radicals with variety of acceptor side chains. Dihyropyrroles made in good yields from O-phenyl containing pent-4-ene acceptors. The analogous process hex-5-enyl did not yield dihydropyridine, probably because the 6-exo-trig ring closure radical was too slow compete H-atom abstraction. precursor...

Oxime carbonates were found to be excellent precursors for the clean and direct generation of iminyl radicals under UV irradiation. Suitably functionalised iminyls underwent cyclisations yielding various phenanthridines also substituted quinolines isoquinolines. EPR X-ray analyses oxime provided insight into mechanism.

Type 1 15-hydroxyprostaglandin dehydrogenase (PGDH) is the main enzyme responsible for metabolism of prostaglandin E2 (PGE2) and PGF2 alpha. To examine possibility that a deficiency PGDH might contribute to preterm labor, we measured localization immunoreactive (IR-) PGDH, mRNA, activity in chorio-decidua, placenta, amnion patients after term elective cesarean section (n = 9), spontaneous vaginal delivery 10), at idiopathic labor (PTL) absence infection (< 36 weeks gestation; n 11)....

Suites of new precursors designed around a cyclohexadiene core and intended to mediate "clean" radical chain syntheses have been prepared tested. 1-Functionalized cyclohexa-2,5-dienes were found readily donate H-atoms, the resulting cyclohexadienyl radicals rapidly extruded their functional group as free radical, because this β-scission restored aromaticity ring. This concept was employed generate designer from esters corresponding alcohols with 1-methyl- or...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe kinetics and orientation of free-radical addition to olefinsJohn M. Tedder John C. WaltonCite this: Acc. Chem. Res. 1976, 9, 5, 183–191Publication Date (Print):May 1, 1976Publication History Published online1 May 2002Published inissue 1 1976https://pubs.acs.org/doi/10.1021/ar50101a003https://doi.org/10.1021/ar50101a003research-articleACS PublicationsRequest reuse permissionsArticle Views782Altmetric-Citations111LEARN ABOUT THESE METRICSArticle...

A wide range of biologically active compounds contain the quinazoline ring system. new free-radical-based method making functionalized quinazolines is described, which relies on microwave-promoted reactions O-phenyl oximes with aldehydes. small set 2-aminoaryl alkanone was prepared and shown to produce dihydroquinazolines when mixed an aldehyde in toluene subjected microwave heating. When ZnCl(2) included reaction mixture, fully aromatic were produced high yields by a rapid convenient...

Fifteen second-generation NHC-ligated boranes with aryl and alkyl substituents on boron were prepared, their radical chemistry was explored by electron paramagnetic resonance (EPR) spectroscopy calculations. Hydrogen atom abstraction from NHC-BH(2)Ar groups produced boryl radicals akin to diphenylmethyl spin extensively delocalized across the NHC, BH, units. All of NHC-B·HAr studied abstracted Br-atoms bromides. Radicals bulky N,N'-dipp underwent dimerization about 2 orders magnitude more...

Under dry, anaerobic conditions, TiO(2) photocatalysis of carboxylic acid precursors resulted in carbon-carbon bond-forming processes. High yields dimers were obtained from treatment acids alone. On inclusion electron-deficient alkenes, efficient alkylations achieved with methoxymethyl and phenoxymethyl radicals. In reactions maleic anhydride or maleimides, phenoxyacetic produced chromenedione derivatives addition to adducts. These photocatalytic are simple cheap perform, the is easily...

A set of oxime carbamates having N-alkyl and N,N-dialkyl substituents were prepared via carbonyldiimidazole intermediates. It was shown by EPR spectroscopy that they underwent clean homolysis their N-O bonds upon UV photolysis. During photolysis acetophenone O-allylcarbamoyl oxime, the corresponding oxazolidin-2-onylmethyl radical detected spectroscopy, providing first evidence N-monosubstituted carbamoyloxyl radicals can hold structural integrity. N,N-Disubstituted dissociated rapidly at...

We treated human lung epithelial cells, type BEAS-2B, with 10-80 microg/cm2 of dust from soils and road surfaces in the western United States that contained particulate matter (PM) < 2.5 microm aerodynamic diameter. Cell viability cytokine secretion responses were measured at 24 hr. Each sample is a complex mixture containing particles different minerals mixed biogenic anthropogenic materials. determined particle chemical composition using methods based on U.S. Environmental Protection...