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At least 1,099 records · Page 61Linked to original sources
PubMed2003

New strategy for convergent steroid synthesis.

We published recently our results on a new and convergent synthesis of natural steroids. The strategy was based on a cycloaddition reaction of Nazarov reagents 2 and 5 with cyclohexenones 1 and 4. In this paper we report results that deal with the synthesis of two new bicyclic Nazarov reagents (13 and 19) and their cycloaddition with two cyclohexenones (1 and 4). These new results constitute an important improvement concerning the versatility of the strategy since tetracycles having the stereochemistry found in natural steroids are now available.

Catalysis↗
PubMed2003

Synthesis of (-)-tetrodotoxin: preparation of an advanced cyclohexenone intermediate.

The preparation of an advanced intermediate toward the enantioselective synthesis of tetrodotoxin is outlined. The enantiomerically pure cyclopentene 15 was generated from ketone 14 by alkylidene carbene insertion with retention of absolute configuration. An ozonolysis/aldol sequence first produced the trans cyclohexenone, which upon epimerization gave the more stable cis enone 18.

Cyclohexanones↗
PubMed2004

Novel synthesis of highly functionalized 14-beta-hydroxysteroids related to batrachotoxin and ouabain.

The use of anionic polycyclization was investigated in an effort to develop a versatile and convergent synthesis of advanced tetracyclic intermediates of batrachotoxin and ouabain analogues. Two new 5-(trialkylsilyl)-2-cyclohexenones as A ring precursors and a new Nazarov intermediate (D ring precursor) were prepared for this purpose. The reaction of the unsaturated beta-keto aldehyde A ring precursor with the enolate of the Nazarov intermediate afforded, after subsequent transformations, a 14-beta-hydroxysteroid with complete control of stereochemistry.

Batrachotoxins↗
PubMed2004

Modeling substituent and conformational effects on the reactivity of antitumor agents containing a cyclopropylcyclohexadienone subunit.

The uncatalyzed alkylation reactions of ammonia by the parent spirocyclopropylcyclohexadienone (6), its 3-amino analogue (7), the cyclic derivative (8), its N-formyl derivative (9), and a closer model (10) of the CPI (1-4) drugs have been investigated in gas phase and in water solvent bulk, using density functional theory at the B3LYP level with several basis sets and the C-PCM solvation model. The effect of several structural key features such as the vinylogous amide conjugation, the acylation of the 2-amino substituent, the ring constraint of the heterocyclic nitrogen atom at C(2) carbon in a ring, and the presence of a condensed pyrrole ring on the reaction activation energy have been investigated. Substrate 7, which is a flexible conformational model of the cyclopropylpyrroloindole moiety (CPI) contained in the duocarmycins, has been used to model the shape-dependent reactivity of these drugs, in gas phase and water solutions. The calculations indicate that shape dependence of reactivity is strongly operative both in gas phase and in polar solvents, since conformational effects are capable of reducing the reaction activation energy by -8.4 and -4.3 kcal mol(-1) in gas phase and in water solution, respectively, that is required to promote "conformational catalysis".

Antineoplastic Agents↗
PubMed2005

Enantio- and diastereoselective total synthesis of EI-1941-1, -2, and -3, inhibitors of interleukin-1beta converting enzyme, and biological properties of their derivatives.

[reaction: see text] The first asymmetric total synthesis of EI-1941-1, -2, and -3, inhibitors of the interleukin-1beta converting enzyme (ICE), has been accomplished, starting from a chiral epoxy iodoquinone 11, a key intermediate in our total synthesis of epoxyquinols A and B. Despite a failure to synthesize the inhibitors by our postulated biosynthetic route, we were able to diastereoselectively synthesize them via an intramolecular carboxypalladation with the key steps being a 6-endo cyclization mode followed by beta-hydride elimination. The investigation of the biological properties of EI-1941-1, -2, and -3 and their derivatives disclosed them to be potent and effective ICE inhibitors with less cytotoxicity than EI-1941-1 and -2 in a cultured cell system.

Caspase Inhibitors↗
PubMed2006

3He NMR as a sensitive probe of fullerene reactivity: [2 + 2] photocycloaddition of 3-methyl-2-cyclohexenone to C70.

The [2 + 2] photoadditions of 3-methyl-2-cyclohexenone to C70 and 3He@C70 have been studied by a combination of HPLC chromatography and FAB-MS, as well as IR and 1H and 3He NMR spectroscopies. The total yield of the mixture of monoadducts was 55% (67% on the basis of the recovered C70). The use of 3He NMR was especially powerful in determining the regioselectivity of the photoaddition reaction of enone to C70. Results of the 3He NMR experiments conducted on the product mixture implicate the two [6,6] bonds closest to the poles of the fullerene (C1-C2 and C5-C6) in the photoaddition process. This reaction mode is analogous to that of most thermal addition reactions to C70. Separation and characterization of the product mixture shows that eight distinct monoadducts are formed in the photoaddition, namely, the four diastereomeric adducts to the C1-C2 and C5-C6 bonds of the C70 cage, each consisting of cis- and trans-fused isomers in a ratio of 2:3. The major mode of photoaddition, accounting for 65% of the product mixture, involves addition to the C1-C2 bond of the ovoid fullerene. Mechanistic implications of these findings are discussed.

Adenine↗
PubMed2006

1H NMR, 13C NMR, and computational DFT studies of the structure of 2-acylcyclohexane-1,3-diones and their alkali metal salts in solution.

1H and 13C NMR spectra of 2-acyl-substituted cyclohexane-1,3-diones (acyl = formyl, 1; 2-nitrobenzoyl, 2; 2-nitro-4-trifluoromethylbenzoyl, 3) and lithium sodium and potassium salts of 1 have been measured. The compound 3, known as NTBC, is a life-saving medicine applied in tyrosinemia type I. The optimum molecular structures of the investigated objects in solutions have been found using the DFT method with B3LYP functional and 6-31G** and/or 6-311G(2d,p) basis set. The theoretical values of the NMR parameters of the investigated compounds have been calculated using GIAO DFT B3LYP/6-311G(2d,p) method. The theoretical data obtained for compounds 1-3 have been exploited to interpret their experimental NMR spectra in terms of the equilibrium between different tautomers. It has been found that for these triketones an endo-tautomer prevails. The differences in NMR spectra of the salts of 1 can be rationalized taking into account the size of the cation and the degree of salt dissociation. It seems that in DMSO solution the lithium salt exists mainly as an ion pair stabilized by the chelation of a lithium cation with two oxygen atoms. The activation free energy the of formyl group rotation for this salt has been estimated to be 51.5 kJ/mol. The obtained results suggest that in all the investigated objects, including the free enolate ions, all atoms directly bonded to the carbonyl carbons lie near the same plane. Some observations concerning the chemical shift changes could indicate strong solvation of the anion of 1 by water molecules. Implications of the results obtained in this work for the inhibition mechanism of (4-hydroxyphenyl) pyruvate dioxygenase by NTBC are commented upon.

4-Hydroxyphenylpyruvate Dioxygenase↗
PubMed2001

Antioxidant principles from Bauhinia tarapotensis.

A new cyclohexenone (1) and a new caffeoyl ester derivative (2), together with the known compounds (-)-isolariciresinol 3-alpha-O-beta-D-glucopyranoside (3), (+)-1-hydroxypinoresinol 1-O-beta-D-glucopyranoside (4), isoacteoside (5), luteolin 4'-O-beta-D-glucopyranoside (6), and indole-3-carboxylic acid (7), were isolated from the leaves of Bauhinia tarapotensis. The structures of these new compounds were determined by spectroscopic data analysis. The antioxidant activities of 1-7 were determined by measuring their free radical scavenging effects, using the 1,1-diphenyl-2-dipicrylhydrazyl free radical (DPPH) and Trolox equivalent antioxidant activity (TEAC) methods, and the coupled oxidation of beta-carotene and linoleic acid. Compounds 3-5 showed good activities in the DPPH and TEAC tests, while compounds 1 and 2 were active in the coupled oxidation of beta-carotene and linoleic acid bioassay.

Antioxidants↗
PubMed2002

Parasitenone, a new epoxycyclohexenone related to gabosine from the marine-derived fungus Aspergillus parasiticus.

Bioassay-guided fractionation of an organic extract of the broth from the marine-derived fungus culture of Aspergillus parasiticus led to the isolation and subsequent structural elucidation of a new gabosine derivative, parasitenone (1), and two known benzyl alcohols, 3-chloro-4,5-dihydroxybenzyl alcohol (2) and gentisyl alcohol (3). The benzyl alcohols (2, 3) were identified as the principal free radical scavenging components. Parasitenone (1) also showed moderate activity in the free radical scavenging assay.

Acetylation↗
PubMed2003

Three new malyngamides from a Papua New Guinea collection of the marine cyanobacterium Lyngbya majuscula.

Three new malyngamides, U (1), V (2), and W (3), all possessing an uncommon oxygenation pattern, have been isolated from the marine cyanobacterium Lyngbya majuscula collected in Papua New Guinea. The planar structures of these compounds were deduced from NMR data. Aspects of their relative stereochemistry were investigated using selective (1)H decoupling, 1D and 2D NOESY, and E-COSY experiments in three different NMR solvents.

Animals↗
PubMed2005

Sorbicillin analogues and related dimeric compounds from Penicillium notatum.

In our screening of microorganisms for new natural products, the fungus Penicillium notatum delivered further members of the sorbicillin family, namely, the sohirnones A [3, 1-(2,4-dihydroxy-5-methylphenyl)hex-4-en-1-one], B [4a, 1-(2,4,5-trihydroxy-3,6-dimethylphenyl)hexa-2,4-dien-1-one], and C [5, 1-(2,4,5-trihydroxy-3,6-dimethylphenyl)hex-4-en-1-one]. A stable tautomer of oxosorbicillinol (7) was characterized as 6, and the recently described 7-deacetoxyyanuthone (8) was reisolated. The additionally isolated rezishanones A-D (12-13c) are the first natural Diels-Alder products of sorbicillinol (1) with dienophiles not related with 1. The monomers and dimers showed weak antibacterial activity, but were inactive against fungi and algae. The structures were determined by spectroscopic methods and by comparison of the NMR data with those of the structurally related 2',3'-dihydrosorbicillin (2) and, in the case of 4a, by transformation into the known sorrentanone (4b).

Anti-Bacterial Agents↗
PubMed2006

A sorbicillinoid urea from an intertidal Paecilomyces marquandii.

A ureido Diels-Alder adduct of sorbicillinol 3 has been isolated from an intertidal marine Paecilomyces marquandii strain, in a screening for new natural products. The structure was determined by spectroscopic methods, and the relative stereochemistry was confirmed by molecular modeling. The absolute stereochemistry was deduced by comparison of the CD curves with those of known members of the bisorbicillinol family. This is the first report of the isolation of a ureido sorbicillinol derivative.

Cyclohexanones↗
PubMed1983

Mammalian drug metabolism.

Drugs and other chemicals that do not occur in mammalian systems are metabolized by a wide variety of enzymes. Reactions catalyzed by these enzymes have been classified into two general phases. Phase I reactions include oxidations, reductions, and hydrolyses, whereas Phase II reactions are broadly defined as conjugation reactions and include glucuronidation, sulfation, acylation, methylation, and conjugation with glutathione. The mechanisms of these biotransformations are outlined to demonstrate how both non-toxic and toxic metabolites are produced. The mammalian metabolism of acetaminophen, a widely used mild analgesic, and R-(+)-pulegone, the major constituent terpene of pennyroyal oil, will be discussed to illustrate specific features of mammalian drug metabolism.

Abortifacient Agents↗
PubMed1992

Isolation and identification of xochitloldione and isoxochitlolone from Cnidosculus urens.

Major components of MeOH extracts from the plant roots of Cnidosculus urens purified by cc and tlc and crystallization were lupeol acetate and the previously unreported compounds isoxochitlolone [1] and xochitloldione [2], which were identified through mass, ir, nmr, and uv spectroscopy and X-ray crystallography. In preliminary testing, isoxochitlolone has been found to be active against Escherichia coli and Staphylococcus aureus.

Anti-Bacterial Agents↗
PubMed1995

Malyngamide H, an ichthyotoxic amide possessing a new carbon skeleton from the Caribbean cyanobacterium Lyngbya majuscula.

Guided by ichthyotoxic activity against goldfish, a new lipopeptide, malyngamide H [1], and its corresponding free acid, 7-methoxytetradec-4(E)-enoic acid [2], have been isolated from the tropical marine cyanobacterium Lyngbya majuscula. The structure of the new carbon skeleton borne by malyngamide H was elucidated on the basis of spectroscopic analysis, mainly 2D nmr. The absolute stereochemistry of the cyclohexenone moiety of malyngamide H [1] was deduced by a combination of 2D NOESY and exciton chirality circular dichroism spectroscopy.

Animals↗
PubMed1998

Two new cytotoxic compounds from Tapirira guianensis.

Two new cytotoxic compounds, 2-[10(Z)-heptadecenyl]-1,4-hydroquinone (1) and (4R,6R)-dihydroxy-4-[10(Z)-heptadecenyl]-2-cyclohexenone (2) have been isolated from a MeOH extract of seeds of Tapirira guianensis. The structures were established through spectral analysis of the isolates and their derivatives.

Acetylation↗