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N-Cycloalkanoyl-L-phenylalanine derivatives as VCAM/VLA-4 antagonists.

A systematic structure-activity relationship investigation of the lead compound 1 resulted the identification of several N-[(substituted alkyl)cycloalkanoyl]-4-[((2,6-dichlorophenyl)carbonyl)amino]-L-phenylalanine derivatives as potent VCAM/VLA-4 antagonists. The data are consistent with a model of these compounds in which these alkanoylphenylalanines reside in a compact gauche (-) bioactive conformation.

Crystallography, X-Ray↗

New generation dopaminergic agents. 5. Heterocyclic bioisosteres that exploit the 3-OH-N1-phenylpiperazine dopaminergic template.

The synthesis of several bioisosteric analogs based on the 3-OH-N1-phenylpiperazine dopamine D2 agonist template (i.e., 4) is described. The indolone (5) and 2-CF3-benzimidazole (13) were observed to have excellent affinity for the D2 receptor. Several D4 selective compounds were also identified. Molecular modeling studies and a putative bioactive conformation are discussed.

Animals↗

Introduction of a cis-prolyl mimic in position 7 of the peptide hormone oxytocin does not result in antagonistic activity.

New insights into the structure-activity relationship of the peptide hormone oxytocin are presented. Incorporation of the novel cis-prolyl mimic 2,2-dimethyl-1,3-thiazolidine-4-carboxylic acid (pseudoproline, PsiPro) at position 7 of the hormone yielded the analogue [Cys(Psi(Me,Me)pro)]7oxytocin (1) that showed a 92-95% induction of the cis peptide bond conformation between Cys6 and PsiPro7, as determined by one- and two-dimensional NMR spectra in water and in DMSO-d6. The impact of the dimethyl moiety regarding conformation and bioactivity was investigated by the synthesis of the corresponding dihydro compound, [Cys(Psi(H,H)pro)]7oxytocin (2). Biological tests of the uterotonic activity, the pressor activity, and the binding affinity to the rat and human oxytocin receptors were carried out. As a most significant result, no antagonistic activities were found for both the cis-constrained analogue 1 and analogue 2, suggesting that a cis conformation between residues 6 and 7 of the molecule does not result in antagonistic activity. However, the about 10-fold reduction in agonistic activity of 1 as compared to oxytocin is consistent with the reduction of the trans conformation from 90% for oxytocin to 5-8% for compound 1. Compound 1 retained a high binding affinity for the oxytocin receptor, with K(i) values of 8.0 and 1.9 nM for the rat and the human receptor, respectively. The correlation between the biological activities and the cis contents obtained from NMR analysis for compounds 1, 2, and oxytocin leads to the hypothesis that a cis/trans conformational change plays an important role in oxytocin receptor binding and activation.

Animals↗

Helical structure of tercyclopropanedimethanol in solution.

Oligocyclopropanes with repetitive stereochemistry occur in two unusual natural products with interesting bioactivity. X-ray crystal structures are available for these compounds but with partially contradicting results. Because the 1H and 13C NMR spectra of oligocyclopropanes are far from trivial to be assigned even at highest magnetic fields, we have prepared a specifically deuterated sample and have applied high field NMR spectroscopy and DFT calculations to determine its conformation. The helix with equal handedness shown in the stereopicture was found for tercyclopropanedimethanol. A dihedral angle of around +40 degrees is the best representation of the experimental data and characterizes, therefore, the dominating helical conformation of tercyclopropanedimethanol with a single repetitive (+)-gauche interunit dihedral angle. This is in full agreement with the crystal structure of the all syn,trans-quinquecyclopropanedimethanol with an R configuration at the termini that also adopted an all (+)-gauche conformation. However, the crystal structure of the title compound and the solution structure are different.

Crystallography, X-Ray↗

Defensive chemistry of Senecio miser.

Three eremophilanolides, 1alpha-acetoxy-8beta-methoxy-10betaH-eremophil-7(11)-en-8alpha,12-olide (1); 1alpha-angeloyloxy-6beta-hydroxy-8beta-methoxy-10betaH-eremophil-7(11)-en-8alpha,12-olide (2); and 1alpha-angeloyloxy-8betaH,10betaH-eremophil-7(11)-en-8alpha,12-olide (3), and two pyrrolizidine alkaloids, integerrimine (4) and its N-oxide (5), were isolated from bioactive fractions of Senecio miser. The structures of the new compounds 1 and 2 were established by NMR spectroscopic analysis and chemical transformation. The X-ray analysis of compound 1 was also performed. Eremophilanolides 1 and 2 and alkaloids 4 and 5 were found to be strong insect antifeedants, further supporting a proposed defensive role for these classes of compounds.

Animals↗

Two new bioactive monotetrahydrofuran Annonaceous acetogenins from the bark of Xylopia aromatica.

Xylopien [1] and xylomatenin [2], two new bioactive monotetrahydrofuran Annonaceous acetogenins, have been isolated from an EtOH extract of the bark of Xylopia aromatica, using bioactivity-directed fractionation employing lethality to brine shrimp. These new compounds each have a double bond in the hydrocarbon chain and have been identified as C-23, C-24 dehydro analogs of xylopiacin and xylomaticin. Their structures were elucidated by spectral analyses of the parent compounds and/or simple chemical derivatives. Their absolute stereochemistries have been established by 1H- and 2D nmr experiments utilizing the production of Mosher esters. These acetogenins showed cytotoxic potencies superior to adriamycin against three human solid tumor cell lines.

4-Butyrolactone↗

Additional bioactive acetogenins, annomutacin and (2,4-trans and cis)-10R-annonacin-A-ones, from the leaves of Annona muricata.

In a continuation of our research on bioactive components from the leaves of Annona muricata, three novel monotetrahydrofuran Annonaceous acetogenins, namely, annomutacin [1], (2,4-trans)-10R-annonacin-A-one [2], and (2,4-cis)-10R- annonacin-A-one [3], have been identified. Their structures were deduced by ms, nmr, ir, and uv spectral and chemical methods, and the absolute configurations were determined by Mosher ester methodology. A known bioactive amide, N-p-coumaroyl tyramine, was also found. Compound 1 and the mixture of compounds 2 and 3 showed selective cytotoxicities against the human A-549 lung tumor cell line.

4-Butyrolactone↗

Chemistry of puupehenone: 1,6-conjugate addition to its quinone-methide system.

The marine natural product puupehenone (1), isolated in good yields from sponges of the genus Hyrtios, has been shown to undergo stereospecific 1,6-conjugate addition to its quinone-methide system. Several nucleophilic agents such as hydrogen cyanide, Grignard reagents, and nitroalkanes were studied, producing structurally diverse compounds. This lead optimization study was initiated due to the bioactivity of puupehenone and its natural analogues, which includes numerous previous reports of potential anticancer and antiinfective activity.

Animals↗

Potential metabolic bioactivation pathways involving cyclic tertiary amines and azaarenes.

A major theme explored in this review is the MAO-and cytochrome P450-catalyzed alpha-carbon oxidations of selected cyclic tertiary amines to give iminium metabolites that undergo further chemical modifications to form known or potentially toxic products. The most dramatic illustration of this type of bioactivation process is the conversion of the parkinsonian-inducing neurotoxin MPTP (23) by brain MAO-B to the iminium (dihydropyridinium) metabolite 24 which is oxidized further to the pyridinium species MPP+ (25). The selective destruction of nigrostriatal neurons by MPP+ is dependent on a unique sequence of events (transport into the nerve terminals by the dopamine transporter, localization in the inner mitochondrial membrane by electromotive forces, and inhibition of complex I of the mitochondrial electron transport chain) that, fortunately, are unlikely to be encountered with many substances. A second example of a well-documented metabolic bioactivation sequence involves the highly toxic pyrrolizidine alkaloids (102). These compounds undergo cytochrome P450-catalyzed alpha-carbon oxidation which converts the 3-pyrrolinyl moiety present in the parent alkaloids into a pyrrolyl-containing metabolite (105). The presence of labile functional groups results in the spontaneous conversion of 105 to reactive electrophilic products (106 and 108) that undergo Michael addition reactions with nucleophiles on biomacromolecules leading to a variety of toxic outcomes. Less clearly defined are the potential contributions to neurodegenerative processes that may be mediated by low-level, long term exposure to less potent toxins. Examples of potential proneurotoxins are the endogenously formed tetrahydroisoquinolines (such as 40-50) and tetrahydro-beta-carbolines (such as 54) that may be biotransformed to neurotoxic isoquinolinium (such as 51) and beta-carbolinium (such as 52) species in the brain. A similar argument can be made for 4-piperidinols (compounds that are at the same oxidation state as the tetrahydropyridines) which may be metabolized via iminium intermediates to amino enols that spontaneously convert to dihydropyridinium species and hence to pyridinium metabolites (67-->68-->69-->70-->71, Scheme 10). This type of reaction sequence has been well documented with the parkinsonian-inducing neuroleptic agent haloperidol (72) which is metabolized in humans, baboons, and rodents to the pyridinium species HPP+ (75), a potent inhibitor of mitochondrial respiration. Finally, an appreciation of the alpha-carbon oxidations of fully reduced azacycles such as (S)-nicotine (61) and phencyclidine (82) to chemically reactive metabolites that form covalent adducts with proteins, including the enzymes that are responsible for their formation, may prove of toxicological importance when attempting to account for the effects of chronic abuse of these potent drugs.1

Amines↗

Rational design and synthesis of new quorum-sensing inhibitors derived from acylated homoserine lactones and natural products from garlic.

Parallel solution-phase synthesis of sulfide AHL analogues (10a-s) by one-pot or a sequential approach is reported. The corresponding sulfoxides 13a-e and sulfones 14a-e were prepared to expand the diversity of the 19-member array of sulfides . Likewise, dithianes 12a-c were prepared with similarity both to sulfides 10a-s and to bioactive structures from garlic. Design and biological screening of all compounds presented in this work targeted inhibition of quorum-sensing comprising competitive inhibition of transcriptional regulators LuxR and LasR. The design was based on critical interactions within the binding-site and structural motifs in molecular components isolated from garlic, 7 and 8, shown to be quorum-sensing inhibitors but not antibiotics. A potent quorum-sensing inhibitor N-(heptylsulfanylacetyl)-l-homoserine lactone (10c) was identified. Together with data collected for the other analogues, the resulting structure-activity relationship led to a hypothesis in which competitive binding was assumed.

4-Butyrolactone↗

Identification and occurrence of the bioactive beta-carbolines norharman and harman in coffee brews.

Norharman and harman, two heterocyclic beta-carboline alkaloids with biological activity, were found in brewed coffee. Identification and analysis were carried out by HPLC-MS and RP-HPLC-fluorescence, respectively. All tested samples of brewed coffee including ground coffee, decaffeinated coffee, instant coffee and espresso contained both norharman and harman in variable amounts. Norharman was the major beta-carboline alkaloid in brewed coffee at levels up to 9.34 microg g(-1) in instant ground coffee compared with harman, which had levels up to 1.67 microg g(-1). The two beta-carbolines appeared to be formed during roasting of the coffee beans. It is concluded that drinking coffee is a major exogenous dietary source of these bioactive beta-carboline alkaloids previously reported as mild psychoactive compounds in animal studies and in vitro co-mutagens. These results support our previous conclusion that foods containing beta-carbolines are an important exogenous source of these alkaloids in humans.

Alkaloids↗

4-Hydroxynonenal as a biological signal: molecular basis and pathophysiological implications.

Reactive oxygen intermediates (ROI) and other pro-oxidant agents are known to elicit, in vivo and in vitro, oxidative decomposition of omega-3 and omega-6 polyunsaturated fatty acids of membrane phospholipids (i.e, lipid peroxidation). This leads to the formation of a complex mixture of aldehydic end-products, including malonyldialdehyde (MDA), 4-hydroxy-2,3-nonenal (HNE), and other 4-hydroxy-2,3-alkenals (HAKs) of different chain length. These aldehydic molecules have been considered originally as ultimate mediators of toxic effects elicited by oxidative stress occurring in biological material. Experimental and clinical evidence coming from different laboratories now suggests that HNE and HAKs can also act as bioactive molecules in either physiological and pathological conditions. These aldehydic compounds can affect and modulate, at very low and nontoxic concentrations, several cell functions, including signal transduction, gene expression, cell proliferation, and, more generally, the response of the target cell(s). In this review article, we would like to offer an up-to-date review on this particular aspect of oxidative stress--dependent modulation of cellular functions-as well as to offer comments on the related pathophysiological implications, with special reference to human conditions of disease.

Aldehydes↗

(4S,5S)-4-[(1R)-1,2-Dihydroxyethyl]-5-tridecyl-1,3-oxazolidin-2-one.

The title compound, C(18)H(35)NO(4), is a new bioactive amphiphilic lipid with a cis-substituted 1,3-oxazolidin-2-one head group. In the crystal structure, the molecules form intercalating bilayers in which the oxazolidinone head groups are joined together by hydrogen bonds into chains.

Journal Article↗

Screening for biologically active metabolites with endosymbiotic bacilli isolated from arthropods.

Endosymbiotic bacteria from the genus Bacillus were isolated from different compartments of the gut of various members of insects (Hexapoda) and millipedes (Diplopoda). They were grown in submerged culture and investigated by biological assays and HPLC-diode array analysis regarding their production of bioactive metabolites, which were isolated and determined in structure. Known compounds and yet unknown derivatives from the primary metabolism were detected, as well as antibacterially and antifungally acting peptide antibiotics.

Animals↗

The biochemistry and physiology of S-nitrosothiols.

S-nitrosothiols are biological metabolites of nitric oxide. It has often been suggested that they represent a more stable metabolite of nitric oxide that can either be stored, or transported, although the evidence for this is sparse. There are many unanswered questions concerning how S-nitrosothiols are formed, how they are metabolized and how they elicit biological responses. These questions are highlighted by the fact that the known chemistry of nitric oxide, thiols, and S-nitrosothiols cannot serve to explain their proposed biological activities. This review attempts to highlight the gulf between our chemical understanding of S-nitrosothiols and the proposed biological activities of these compounds with respect to guanylyl cyclase-independent nitric oxide bioactivity and also the control of vascular tone.

Animals↗

Modulation of the immune response by anaphylatoxins.

Bioactive C3a and C5a fragments derived from the human complement compounds C3 and C5, respectively, possess immunoregulatory activities. C3a and C5a differentially influence in vitro immune function. C3a was found to be a potent suppressor of antigen-specific and polyclonal antibody responses. In contrast, C3a was unable to suppress antigen-or mitogen-induced B and T cell proliferation. Analyses of synthetic peptides based on the sequences of C3a revealed that the carboxy-terminal region of the molecule is responsible for immunosuppression. C3a-mediated suppression occurs through the activation of a nonspecific suppressor T cell pathway. In contrast to the results obtained with C3a, C5a was found to augment both in vitro humoral and cell-mediated immune responses. Regulation of immune function by complement components may form part of an in vitro nonspecific immunoregulatory network.

Adjuvants, Immunologic↗

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates adenylate cyclase and promotes proliferation of mouse primordial germ cells.

During migration and for about 2 days after their arrival in the gonadal ridges, primordial germ cells (the embryonic precursors of gametes of the adult animal) proliferate actively. Certain growth factors, such as stem cell factor and leukemia inhibitory factor, seem to be essential for survival, proliferation and possibly differentiation of mouse primordial germ cell in vivo and/or in vitro. Similarly, increase in intracellular cAMP is followed by a marked enhancement of primordial germ cell proliferation, at least in culture. In the present study, we show that pituitary adenylate cyclase-activating polypeptides (PACAP-27 and PACAP-38), two neuropeptides of the secretin-glucagon-vasoactive intestinal polypeptide-GH-releasing hormone family, stimulate in vitro proliferation of mouse primordial germ cells, bind to primordial germ cells and gonadal somatic cells (possibly to type I PACAP receptor) and activate adenylate cyclase in the same cells. Moreover, PACAP-like immunoreactivity was found in gonadal ridges, mostly on germ cell surface. In conclusion, evidence is provided that PGC proliferation can be stimulated by certain bioactive polypeptides, thus suggesting a novel regulatory role for such compounds in early gonad development.

Adenylyl Cyclases↗

How significant are environmental estrogens to women?

Women are exposed to xenobiotic estrogens at least to the same extent as men. These estrogenic chemicals are either from plant material in the diet (phytoestrogens) or from industrial sources. Mainly industrially derived environmental estrogens may accumulate within the food chain and persist in human adipose tissue. In contrast, phytoestrogens do not bioaccumulate and are rapidly excreted in urine. The phytoestrogens probably represent the source of most extensive exposure for humans. Epidemiological evidence suggests that diets rich in phytoestrogens are associated with reduced incidences of cardiovascular disease, breast cancer, prostate cancer and osteoporosis. The numerous bioactivities (other than just estrogenicity) of phytoestrogens and related dietary compounds make it difficult to single out the mechanisms mediating such protective effects. The possibility that the newly discovered estrogen receptor beta may be an important modulator of phytoestrogen action is opening up new lines of research. While the evidence suggests that phytoestrogens may be of positive relevance to postmenopausal women, indications that exposure of women to industrially derived xenobiotic estrogens provides risks to health remain unproven. Further work is necessary to clarify the relative importance of 'xenobiotic' estrogens to human health, but it must be emphasized that the estrogenic potency of all the xenobiotic estrogens is very low compared with that of endogenous estrogens.

Breast Neoplasms↗