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PubMed2000

Metabolites from a marine bacterium Pseudomonas/Alteromonas, associated with the sponge Dysidea fragilis.

The lipophylic extract from a Black Sea bacterium, associated with the sponge Dysidea fragilis, was investigated. Saturated hydrocarbons and fatty acids of the lipids were identified. The concentrations of the polycyclic compounds appeared to be negligible. The main components appeared to be phosphatidyl ethanolamine, followed by phosphatidyl serine. The first was investigated by FAB mass spectrometry and a series of molecular species partially identified.

Alteromonas↗
PubMed1998

Synthesis and evaluation of tacrine-huperzine A hybrids as acetylcholinesterase inhibitors of potential interest for the treatment of Alzheimer's disease.

Seventeen polycyclic compounds related to tacrine and huperzine A have been prepared as racemic mixtures and tested as acetylcholinesterase (AChE) inhibitors. The conjunctive pharmacomodulation of huperzine A (carbobicyclic substructure) and tacrine (4-aminoquinoline substructure) led to compound 7jy, 2.5 times less active than tacrine as AChE inhibitor, but much more active than its (Z)-stereoisomer (7iy). Derivatives 7dy and 7ey, lacking the ethylidene substituent, showed to be more active than tacrine. Many other structural modifications of 7jy led to less active compounds. Compounds 7dy and 7ey also showed to be much more active than tacrine in reversing the partial neuromuscular blockade induced by d-tubocurarine.

Acetylcholinesterase↗
PubMed2000

Enantiomer-selective activation of racemic catalysts.

Asymmetric catalysts can be evolved into highly activated catalysts by association with chiral activators. This asymmetric activation process is particularly useful in racemic catalysis through selective activation of one enantiomer of the racemic catalysts. Recently, a strategy whereby a racemic catalyst is selectively deactivated by a chiral additive has been reported to yield nonracemic products. However, we have reported a strategy that is an alternative to asymmetric catalysts but is conceptually opposite, in which a chiral activator selectively activates rather than deactivates one enantiomer of a racemic chiral catalyst. The advantage of this activation strategy over the deactivation counterpart is that the activated catalyst can produce a greater enantiomeric excess (x(act)% ee) in the products than the ee attained by the enantiomerically pure catalyst on its own. Therefore, 'asymmetric activation' could provide a general and powerful strategy for the use of not only atropisomeric and, hence, racemic ligands but also chirally flexible and 'pro-atropisomeric' ligands without enantiomeric resolution!

Catalysis↗
PubMed2002

Applications of the squarate ester cascade to the expeditious synthesis of hypnophilin, coriolin, and ceratopicanol.

The first applications of the squarate ester cascade to natural products synthesis have been realized. Only 10 laboratory steps mediate the conversion of diisopropyl squarate to (+/-)-hypnophilin (8). Key reactions include a combination of chlorination, reduction, dehydration, and oxidation maneuvers in the proper sequence. A penultimate precursor to 8 has previously been converted into coriolin (9), thereby allowing a formal synthesis of racemic 9 also to be claimed. A rather different strategy was employed to arrive at (+/-)-ceratopicanol (10). Of the seven steps involved, three consisted of the use of lithium in liquid ammonia. The three divergent synthetic objectives realized in these experiments involved (a) generation of an extended enolate anion and its regioselective C-methylation at the gamma-carbon; (b) unprecedented reductive cleavage of a beta-isopropoxy group in a 2,3-diisopropoxy-2-cyclopentenone setting; and (c) conventional conversion of an alpha-alkoxy ketone to the parent carbonyl system. Thus, the appreciable enhancement in structural complexity offered by the squarate cascade holds considerable potential for the concise synthesis of constitutionally intricate targets.

Antibiotics, Antineoplastic↗
PubMed2005

Generation and reaction of tungsten-containing carbonyl ylides: [3 + 2]-cycloaddition reaction with electron-rich alkenes.

Novel tungsten-containing carbonyl ylides 7, generated by the reaction of the o-alkynylphenyl carbonyl derivatives 1 with a catalytic amount of W(CO)(5)(thf), reacted with alkenes to give polycyclic compounds 5 through [3 + 2]-cycloaddition reaction followed by intramolecular C-H insertion of the produced nonstabilized carbene complex intermediates 8. In the presence of triethylsilane, these tungsten-containing carbene intermediates 8 were smoothly trapped intermolecularly by triethylsilane to give silicon-containing cycloadducts 17 with regeneration of the W(CO)(5) species. By this procedure, the scope of alkenes employable for this reaction was clarified. The presence of the tungsten-containing carbonyl ylide 7c was confirmed by direct observation of the mixture of o-ethynylphenyl ketone 1c and W(CO)(5)(thf-d(8)). Careful analysis of the intermediate by 2D NMR, along with the observation of the direct coupling with tungsten-183 employing the (13)C-labeled substrate, confirmed the structure of the ylide 7c. Examination using (E)- or (Z)- vinyl ether revealed that the [3 + 2]-cycloaddition reaction proceeded in a concerted manner and that the facial selectivity of the reaction differed considerably depending on the presence or absence of triethylsilane. These results clarified the reversible nature of this [3 + 2]-cycloaddition reaction.

Journal Article↗
PubMed1983

Tricyclic triarylethylene antiestrogens: dibenz[b,f]oxepins, dibenzo[b,f]thiepins, dibenzo[a,e]cyclooctenes, and dibenzo[b,f]thiocins.

The bridging groups O, S, CH2CH2, and SCH2 were used to produce a series of 26 tricyclic triarylethylenes. Their in vitro binding to rat uterine estrogen receptor was measured in a competitive binding assay. Antifertility and uterotrophic tests in rats showed that antiestrogenic activity was present. The most interesting series had a basic side chain, and the most potent compounds were 3-[2-(dimethylamino)ethoxy] -10-ethyl-11-(4-hydroxyphenyl)dibenzo[b,f]thiepin (7b) and 3-[2-(dimethylamino)ethoxy]-11-ethyl-12-(4-hydroxyphenyl)-5,6-dihydrodibenzo[a,e]-cyclooctene (7c), which had good binding (approximately 50% relative to estradiol) and good antiestrogenic activity (ca. one-half of the potency of tamoxifen, III). In this series, the O-bridged compound was the least active, and this is interpreted in terms of the flatness of the dibenzoxepin ring system. Sedative activity was found in some of the compounds.

Animals↗
PubMed2003

Cascade radical cyclizations of benzannulated enyne-allenes. Unusual cleavage of a benzene ring leading to twisted 1,1'-dialkyl-9,9'-bifluorenylidenes and spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorenes].

Treatment of the benzannulated enediynyl propargylic alcohol 16 (isomer ratio = 2:1) with thionyl chloride induced a sequence of reactions leading to the twisted 1,1'-dipropyl-9,9'-bifluorenylidene 17, the polycyclic compounds 18 and 19, and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 (trans/cis = 5:1). The transformation from 16 to the unexpected 17 presumably involved an initial formation of the benzannulated enyne-allene 21 followed by a C(2)-C(6) cyclization reaction and an intramolecular radical-radical coupling reaction, giving rise to the formal Diels-Alder adduct 23. Repeat of this sequence then furnished 24. Cleavage of the bond connecting the two carbons having the propyl substituent afforded 25. A subsequent rotation of the carbon-carbon bond joining the two central five-membered rings then gave the trans isomer 26. Oxidation of 26, presumably by oxygen, followed by hydrolysis then produced 17. Interestingly, the pathway leading to 17 involved an unusual cleavage of a benzene ring. The X-ray crystal structure of 17 reveals that it has a twist angle of 45.2 degrees for the carbon-carbon double bond connecting the two bifluorenylidene fragments. The spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 20 apparently was produced via two intramolecular [2 + 2] cycloaddition reactions of the benzannulated enyne-allene moieties, generated in situ from the benzannulated enediynyl propargylic alcohols. The twisted 1,1'-dimethyl-9,9'-bifluorenylidene 33 and the spiro[1H-cyclobut[a]indene-1,9'-[9H]fluorene] 39 (trans/cis = 3:1) were likewise produced from 32 and 38, respectively.

Journal Article↗
PubMed2003

New versatile route to the synthesis of tetrahydro-beta-carbolines and tetrahydro-pyrano[3,4-b]indoles via an intramolecular Michael addition catalyzed by InBr3.

A simple multistep synthetic strategy to 4-substituted 1,2,3,4-tetrahydro-beta-carboline and 1,3,4,9-tetrahydro-pyrano[3,4-b]indole derivatives starting from commercially available indole 2-carboxylic acid (5) is described. The final intramolecular Michael addition promoted by catalytic amount of InBr(3) (5-10 mol %) provided the expected polycyclic compounds in excellent yields (up to 97%) both in anhydrous organic and aqueous media.

Journal Article↗
PubMed2005

Total synthesis of epoxyquinols A, B, and C and epoxytwinol A and the reactivity of a 2H-pyran derivative as the diene component in the Diels-Alder reaction.

Full details of two versions of the total synthesis of epoxyquinols A, B, and C and epoxytwinol A (RKB-3564D) are described. In the first-generation synthesis, the HfCl(4)-mediated diastereoselective Diels-Alder reaction of furan with Corey's chiral auxiliary has been developed. In the second-generation synthesis, a chromatography-free preparation of an iodolactone, by using acryloyl chloride as the dienophile in the Diels-Alder reaction of furan, and the lipase-mediated kinetic resolution of a cyclohexenol derivative have been developed. This second-generation synthesis is suitable for large-scale preparation. A biomimetic cascade reaction involving oxidation, 6pi-electrocyclization, and then Diels-Alder dimerization is the key reaction in the formation of the complex heptacyclic structure of epoxyquinols A, B, and C. Epoxytwinol A is synthesized by the cascade reaction composed of oxidation, 6pi-electrocyclization, and formal [4 + 4] cycloaddition reactions. A 2H-pyran, generated by oxidation/6pi-electrocyclization, acts as a good diene, reacting with several dienophiles to afford polycyclic compounds in one step. An azapentacyclic compound is synthesized by a similar cascade reaction composed of the four successive steps: oxidation, imine formation, 6pi-azaelectrocyclization, and Diels-Alder dimerization.

Ascomycota↗
PubMed2004

Highly selective synthesis of bicyclic quinolizidine alkaloids and their analogues via double RCM reaction of N-alkynyl-N-(1,omega)-alkadienyl acrylamides.

The double ring-closing metathesis reaction of N-alkynyl-N-(1,omega)-alkadienyl acrylamides 1 using first- or second-generation Grubbs' catalyst afforded, in a highly selectively manner, the fused bicyclic quinolizidine alkaloid derivatives and their analogues bearing a 1,3-diene moiety, which may further undergo a Diels-Alder reaction with a dienophile to afford N-containing polycyclic compounds. The excellent selectivity of fused/dumbbell-mode cyclization has been realized by the higher reactivity of the electron-rich C=C bond or carbon-carbon triple bond combined with the lower reactivity of the electron-deficient C=C bond toward metallocarbenes and the thermodynamically more stable nature of fused bicyclic compounds 3 vs dumbbell-type bicyclic compounds 4.

Journal Article↗
PubMed2006

Diversity-oriented synthesis of 3-iodochromones and heteroatom analogues via ICl-induced cyclization.

The ICl-induced cyclization of heteroatom-substituted alkynones provides a simple, highly efficient approach to various 3-iodochromones and analogues. This process is run under mild conditions, tolerates various functional groups, and generally provides chromones in good to excellent yields. Subsequent palladium-catalyzed transformations afford a rapid increase in molecular complexity and a convenient preparation of a wide range of functionally substituted chromones, furans, and polycyclic compounds. Iodothiochromenones and iodoquinolinones are also prepared by similar ICl-induced cyclizations.

Catalysis↗
PubMed2006

Cyclopropenes in the 1,3-dipolar cycloaddition with carbonyl ylides: experimental and theoretical evidence for the enhancement of sigma-withdrawal in 3-substituted-cyclopropenes.

The carbonyl ylide dipoles generated by the dirhodium tetra-acetate-catalyzed decomposition of diazocarbonyl precursors 1, 5, and 8 cycloadd to 3-substituted 1,2-diphenylcyclopropenes 3a-e and 3,3-disubstituted cyclopropenes 13, 14, 19, and 20 to give polycyclic compounds with 8-oxatricyclo[3.2.1.0(2,4)]octane and 9-oxatricyclo[3.3.1.0(2,4)]nonane frameworks. Generally, reactions proceed stereoselectively to give adducts of exo stereochemistry with the approach of the carbonyl ylide dipoles from the less-hindered face of cyclopropenes. The electronic properties of the substituent at the C3 position of cyclopropenes play an important role in governing the reactivity of cyclopropenes: when the C3 position is substituted by electron-acceptors such as the methoxycarbonyl or cyano groups, the yields of adducts are decreased significantly or no adducts can be detected at all. Relative reactivities of cyclopropenes were quantified by competition experiments to give the best correlation with sigmaF-Taft constants. Both measured photoelectron spectra and ground-state calculations of a series of 1,2-diphenylcyclopropenes indicate considerable lowering of cyclopropene pi-HOMO energies by substitution with an acceptor group. Such changes in electronic structures of cyclopropenes may cause the inversion of frontier molecular orbital (FMO) interactions from HOMO(cyclopropene)-LUMO(ylide) to LUMO(cyclopropene)-HOMO(ylide) type. In terms of philicity, nucleophilic properties of acceptor-substituted cyclopropenes are diminished to such an extent that these species are no longer good nucleophiles in the reaction with carbonyl ylides, and neither are they good electrophiles, being unreactive. This was shown by the B3LYP calculations of addends.

Journal Article↗