ABSTRACT
It is shown that the bicyclic triaminophosphine P(i-BuNCH2CH2)3N serves as an effective ligand for the palladium-catalyzed amination of a wide array of aryl bromides and iodides. Other bicyclic or acyclic triaminophosphines, even those of similar basicity and/or bulk, were inferior.
ABSTRACT
PhCH=P[MeNCH(2)CH(2)](3)N (1), a semi-stabilized ylide prepared from the commercially available nonionic base P[MeNCH(2)CH(2)](3)N, reacts with aldehydes to give alkenes in high yield with quantitative E selectivity. In contrast with other ylides, this E selectivity is maintained despite changes in the metal ion of the ionic base used to deprotonate 1, temperature, and solvent polarity. In conjunction with structural parameters gained from the X-ray molecular structure of 1, the pathway to E selectivity in these reactions is rationalized by the Vedejs model of Wittig reaction stereochemistry.
ABSTRACT
The hindered nonionic phosphazene base P(4)-t-Bu efficiently deprotonates o-arylmethoxy benzaldehydes, leading to a direct synthesis of benzofurans. Strong ionic bases such as LDA, LiTMP, and KH failed.
Subject(s)
Benzaldehydes , Benzofurans/chemical synthesis , Benzofurans/chemistry , Indicators and Reagents , Molecular Conformation , Molecular Structure , Organophosphorus CompoundsABSTRACT
Extremely strong nonionic superbases of the type P(RNCH(2)CH(2))(3)N catalyze the transesterification of carboxylic acid esters with high selectivity and yields at 25 degrees C. These bases also catalyze the deacetylation of alcohols under mild conditions in quantitative yields. Using enol acetates as acylating agents, primary and secondary alcohols are efficiently protected as acetates through the action of these catalysts. Substituents such as epoxide, carbamate, acetal, oxazoline, nitro, and alkynyl functionalities are tolerated under the reaction conditions. N-Protected peptides undergo clean transesterification without significant racemization, making this methodology potentially very useful.
ABSTRACT
The role of t-butylbicyclophosphorothionate (TBPS) as an antagonist of gamma-aminobutyric acid (GABA) was studied with primary cultures of neurons from the chick embryo cerebrum. The addition of GABA stimulated the uptake of 36Cl- by neurons and the dose dependence of this effect followed hyperbolic kinetics with a K0.5 = 1.3 microM for GABA. TBPS proved to be a potent inhibitor of GABA-dependent Cl- uptake (IC50 = 0.30 microM). Analysis of the kinetics of this process revealed that TBPS is a noncompetitive inhibitor (Ki = 0.15 microM) with respect to GABA. Scatchard analysis of direct binding of [35S]TBPS to membranes isolated from neuronal cultures gave curvilinear plots. These could be resolved by nonlinear regression methods into two components with KD values of 3.1 nM and 270 nM. The TBPS binding constant for this lower affinity site agreed well with the IC50 and Ki values for inhibition of Cl- flux, suggesting that this site is physiologically relevant to GABA antagonism. GABA was a noncompetitive displacer of [35S]TBPS binding to the lower affinity site. The Ki value for this displacement by GABA (1.7 microM) was comparable to the value for GABA enhancement of Cl- flux. The binding of [35S]TBPS to its low-affinity site on neuronal membranes was ninefold higher in the presence of Cl- than with gluconate, an impermeant anion. The rank order for anion stimulation of [35S]TBPS binding was Br- greater than or equal to SCN- greater than Cl- greater than or equal to NO3- greater than I- greater than F- greater than gluconate.(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
Brain/metabolism , Bridged Bicyclo Compounds, Heterocyclic , Bridged Bicyclo Compounds/pharmacology , Bridged-Ring Compounds/pharmacology , Chlorides/metabolism , Ion Channels/metabolism , gamma-Aminobutyric Acid/pharmacology , Animals , Anions , Bridged Bicyclo Compounds/metabolism , Cell Membrane/metabolism , Cells, Cultured , Chick Embryo , Chlorides/pharmacology , Ion Channels/drug effects , Kinetics , Neurons/metabolismABSTRACT
The synthesis of the title compound from 3'-amino-3'-deoxyadenosine in 40% yield is reported. 3'-Amino-3'-deoxyadenosine was made by an improved synthesis in 12 steps from inexpensive D-xylose in 15% overall yield. Both isomers of the title compound, separated by column chromatography, possess confirmed activity against KB tumor cell cultures.
