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At least 307 records · Page 17Linked to original sources
PubMed2006

Amino acid-bearing ROMP polymers with a stereoregular backbone.

The ruthenium-catalyzed ring-opening polymerization (ROMP) of 1-cyclobutenecarbonyl glycine methyl ester provides translationally invariant, head-to-tail ordered polymers. This polybutadiene backbone contains (within the limits of detection) only E-trisubstituted olefins, and it has no stereocenters that would serve as a source of structural ambiguities. Characterization of the polymer products indicates that they have polydispersities ranging from 1.2 to 1.6 and suggests that they are the products of a "living" polymerization. 1-Cyclobutenecarboxamide-derived ROMP polymers are excellent prospects for applications that require stereoregular chains functionalized with polar ligands.

Amino Acids↗
PubMed2006

Circumambulatory rearrangement with characteristics of a 2:1 covalent molecular bevel gear.

anti-W(CO)(5)-complexed 9-methyl-9-phosphabicyclo[6.1.0]nonatriene represents a covalently interlocked molecular bevel gear. Correlated movement of the phosphorus atom and the eight-membered ring by way of a "walk" rearrangement makes gear slippage impossible. The gearing motion is transferred to the four-toothed W(CO)(5) propeller connected to the rotating phosphorus atom, enabling a gearing ratio of 2:1 according to B3LYP and Car-Parrinello Molecular Dynamics calculations. Methyl substitution of the eight-membered ring tempers the gearing process, with the PMeW(CO)(5) entity passing the substituted carbon atom only at temperatures above 50 degrees C.

Bridged Bicyclo Compounds↗
PubMed2006

Studies of the generation and pericyclic behavior of cyclic pentadienyl carbanions. Alkylation reactions as an efficient route to functionalized cis-bicyclo[3.3.0]octenes.

Carbolithiation has been studied with alkyllithium reagents in a series of six- through nine-membered 3-methylene-1,4-cycloalkadienes, efficiently producing the corresponding cyclic pentadienyl carbanions. These pentadienyl anions display unique reactivity, depending on ring size. Cyclooctadienyl anions readily undergo disrotatory electrocyclization to cis-bicyclo[3.3.0]octenyl systems, which are trapped with a variety of electrophiles to stereoselectively provide functionalized cis-bicyclo[3.3.0]octenes. The carbolithiation and electrocyclization processes are examined using low-temperature (1)H NMR experiments. An expedient synthesis of a linear triquinane illustrates this methodology. Electrocyclization of the corresponding cyclononadienyl anion requires unusually high temperatures (120 degrees C), and computational studies provide insights into this change in reactivity. Cycloheptadienyl and cyclohexadienyl anions, generated via carbolithiation, provide functionalized cycloheptadienes and cyclohexadienes upon electrophilic capture. Trapping experiments reveal that the cycloheptadienyl anions are transformed to heptatrienyl anions. A series of experiments have been designed to explore evidence for the feasibility of equilibration of open and closed anionic systems, and these studies report the first isolation of a cis-bicyclo[3.1.0]hexene derived from electrocyclization of a cyclohexadienyl carbanion.

Alkadienes↗
PubMed2006

Organocatalytic transfer hydrogenation of cyclic enones.

The first enantioselective organocatalytic transfer hydrogenation of cyclic enones has been accomplished. The use of iminium catalysis has provided a new organocatalytic strategy for the enantioselective reduction of beta,beta-substituted alpha,beta-unsaturated cycloalkenones, to generate beta-stereogenic cyclic ketones. The use of imidazolidinone 4 as the asymmetric catalyst has been found to mediate the hydrogenation of a large class of enone substrates with tert-butyl Hantzsch ester serving as an inexpensive source of hydrogen. The capacity of catalyst 4 to enable enantioselective transfer hydrogenation of cycloalkenones has been extended to five-, six-, and seven-membered ring systems. The sense of asymmetric induction is in complete accord with the stereochemical model first reported in conjunction with the use of catalyst 4 for enantioselective ketone Diels-Alder reactions.

Catalysis↗
PubMed1993

Structure-based design of inhibitors of purine nucleoside phosphorylase. 2. 9-Alicyclic and 9-heteroalicyclic derivatives of 9-deazaguanine.

Alicyclic and heteroalicyclic derivatives of 9-deazaguanine (2-amino-1,5-dihydro-4H-pyrrolo[3,2-d] [pyrimidin-4-one) are, with one exception, potent inhibitors of purine nucleoside phosphorylase (PNP) equaling the corresponding 9-arylmethyl derivatives previously investigated. The mode of binding of these compounds to PNP was determined by X-ray crystallography.

Binding Sites↗
PubMed1991

N6-substituted adenosine receptor agonists: potential antihypertensive agents.

Adenosine is known to exert a wide range of pharmacological effects including hypotension. This effect of adenosine suggested that modified analogues of adenosine might provide useful antihypertensive agents. Thus, we prepared a series of novel N6-benzocycloalkyladenosines and studied their receptor binding and antihypertensive activity. The structure-activity relationship study shows that the adenosine analogues having the hydrophobic phenyl moiety one carbon away from the C6-nitrogen have modest affinity and selectivity for the A1 receptor, whereas those with the phenyl moiety two carbons away from the C6-nitrogen have excellent affinity and selectivity for the A1 receptor. Many of these analogues showed excellent antihypertensive activity with a wide range of effects on heart rate. There is no direct correlation between the receptor binding affinities and antihypertensive activity; however, it is more closely associated with A1 than A2 affinity. The bradycardic effect of these agonists seems to be due to the A1 affinity. From this set, compound 3 was further evaluated in secondary antihypertensive screens. It lowered the blood pressure dose dependently with effects lasting for over 20 h following administration of a 30 mg/kg dose. Compound 3 was also effective in lowering blood pressure in a renal hypertensive rat model. Thus, appropriately modified N6-substituted adenosines represent a novel class of antihypertensive agents.

Adenosine↗
PubMed1979

Diels-Alder adducts of fulvenes and halogenated dienes. Synthesis and insecticidal activity.

A series of eight adducts (1--8) of substituted fulvenes and polychlorinated cyclodienes was synthesized by Diels-Alder cyclization. The products isolated were the endo bicyclo adducts as determined by detailed 1H and 13C NMR spectral analysis. Steric hindrance of end-product bridge substituents coupled with bulky substituents at C6 of the fulvenes led to one isomeric product in most cases. Compounds 1--8 demonstrated weak insecticidal action in Musca domestica as determined by topical LD50 and oral LC50 assays.

Animals↗
PubMed1976

Importance of the aromatic ring in adrenergic amines. 2. Synthesis and adrenergic activity of some nonaromatic six- and eight-membered ring analogs of beta-phenylethanolamine.

The synthesis of beta-phenylethanolamine analogs in which the phenyl ring is replaced by cyclohexyl, cyclohexen-4-yl, cyclooctyl, cyclooctenyl, cycloocta-1,3-dien-2-yl, cycloocta-1,5-dienyl, and cyclooctatetraenyl was accompanied by conversion of the corresponding aldehydes to the cyanohydrins followed by reduction with lithium aluminum hydride. A preparatively useful synthesis of 1-formylcyclooctatetraene is described utilizing the photocycloaddition of methyl propiolate to benzene followed by reduction to the alcohol and oxidation with MnO2. All compounds, as their hydrochloride salts, exhibited indirect adrenergic activity on the rat vas deferens. On the reserpinized rat vas deferens all compounds potentiated the effects of exogenous norepinephrine. The results are in agreement with the conclusion that the more saturated the ring moiety, the greater the affinity for the amine uptake site of the vas deferens and suggest that there is no important interaction between the drug and this uptake site that involves pi-complex formation.

Adrenergic alpha-Agonists↗
PubMed1976

Hypoglycemic alpha-cycloalkylphenylmehtyl, furanalkyl, and thiophenealkyl lactamimides.

A series of alpha-cycloalkylphenylmethyl lactamimides and a series of furan- and thiophenealkyl lactamimides were prepared for biological evaluation as an extension of earlier finding of hypoglycemic activity in lactamimides. Compounds 7, 20, 23, 25, 29, and 32 produced pronounced hypoglycemia after oral administration to fasted, glucose-primed rats.

Animals↗
PubMed1976

Cycloalkanones. 9. Comparison of analogues which inhibit cholesterol and fatty acid synthesis.

A number of 2,8-dibenzylcyclooctanone analogues inhibited the HMG-CoA reductases activity of Holtzman male rat liver, whereas only 2-octanone, 2-hexadecanone, 2,8-dibenzylcyclooctanone derivatives, and 2-bis(4-chlorophenyl)-3,5-dimethyltetrahydro-4-pyrone inhibited fatty acid synthetase activity. 2-Octanone significantly lowered serum cholesterol, triglycerides, and glycerol levels in Holtzman male rats and serlm cholesterol in male CF1 mice. Serum lipase activity was significantly elevated in rats administered 20 mg/kg/day of 2-octanone for 16 days. The activity of liver HMG-CoA reductase was inhibited in mice administered 10 mg/kg/day of 2-octanone for 10 days and in mouse and rat liver in vitro by 10 mg of 2-octanone. In mice, fecal excretion of [14C]cholesterol and tripalmitin was accelerated whereas palmitic acid and cholesteryl oleate were not affected by 10 mg/kg/day of 2-octanone. The LD50 in male mice for 2-octanone was 1.6g/kg.

Acetate-CoA Ligase↗
PubMed1975

Cycloalkanones. 6. Separation of hypocholesterolemic and antifertility activities in derivatives of 2,8-dibenzylcyclooctanone.

Fluoro and hydroxy derivatives of 2,8-dibenzylcyclooctanone were prepared. Separation of antifertility activity from hypolipidemic and uterotropic effects was achieved with 2,8-bis(4-acetoxybenzyl)cyclooctanone. Some enhancement of the hypolipidemic effect in relation to the uterotropic and antifertility activities was seen in 2,8-bis(4-fluorobenzyl)cyclooctanone. Synthetic methods for the hydroxy compounds are presented.

Animals↗
PubMed1975

Cycloalkanones. 7. Hypocholesterolemic activity of aliphatic compounds related to 2,8-dibenzylcyclooctanone.

A series of 19 aliphatic analogs of 2,8-dibenzylcyclooctanone and 1,5-diphenyl-2,4-dimethyl-3-pentanone was examined. Separation of hypocholesterolemic activity from the previously observed uterotropic and antifertility activities was achieved by simplification of the parent compound to 2-octanone. There was no loss of hypocholesterolemic activity. Reduction of serum cholesterol levels in male rats to less than 50% of control values was obtained at a dose of 10 mg/kg/day.

Animals↗