The tyrosinase inhibitory effects of isoxazolone derivatives with a (Z)-β-phenyl-α, β-unsaturated carbonyl scaffold

Thirteen (Z)-4-(substituted benzylidene)-3-phenylisoxazol-5(4H)-ones were designed to confirm the geometric effect of the double bond of the β-phenyl-α, β-unsaturated carbonyl scaffold on tyrosinase inhibitory activity. Compounds 1a–1m, which all possessed the (Z)-β-phenyl-α, β-unsaturated carbonyl scaffold, were synthesized using a tandem reaction consisting of an isoxazolone ring formation and a Knoevenagel condensation, and three starting materials, ethyl benzoylacetate, hydroxylamine and benzaldehydes. Some of the compounds showed inhibitory activity against mushroom tyrosinase as potent as compounds containing the “(E)”-β-phenyl-α, β-unsaturated carbonyl scaffold. Compounds 1c and 1m showed greater inhibitory activity than kojic acid: IC₅₀?=?32.08?±?2.25?μM for 1c; IC₅₀?=?14.62?±?1.38?μM for 1m; and IC₅₀?=?37.86?±?2.21?μM for kojic acid. A kinetic study indicated that 1m inhibited tyrosinase in a competitive manner and that it probably binds to the enzyme’s active site. In silico docking simulation supported binding of 1m (?7.6?kcal/mol) to the active site of tyrosinase with stronger affinity than kojic acid (?5.7?kcal/mol). Similar results were obtained using cell-based assays, and in B16F10 cells, compound 1m dose-dependently inhibited tyrosinase activity and melanogenesis. These results indicate the anti-melanogenic effect of compound 1m is due to the inhibition of tyrosinase and (Z)-isomer of the β-phenyl-α, β-unsaturated carbonyl scaffold can, like its congener the (E)-isomer, act as an excellent scaffold for tyrosinase inhibition.     

Ionylideneacetic Acids and Abscisic Acid Biosynthesis by Cercospora rosicola

Several compounds having the basic α-ionylideneacetic acid structure were tested in Cercospora rosicola resuspensions. At 100 μm, all the compounds inhibited abscisic acid (ABA) biosynthesis. Time studies with unlabelled and deuterated (2Z,4E)- and (2E,4E)-α-ionylideneacetic acids showed rapid conversions into both (2Z,4E)- and (2E,4E)-4′-keto-α-ionylideneacetic acids as major products. Incorporation of the label into ABA was specific for the 2Z,4E-isomer. Minor products, identified by GC-MS, were (2Z,4E)- and (2E,4E)-4′-hydroxy-α-ionylideneacetic acids and (2Z,4E)-1′-hydroxy-α-ionylideneacetic acid. The conversion to (2Z,4E)-l′-hydroxy-α-ionylideneacetic acid has not been previously reported and was specific for the 2Z,4E-isomer. A time study for the conversion of methyl esters of [²H₃]-(2Z,4E)- and [²H₃]-(2E,4E)-4′-keto-α-ionylideneacetates showed a slow introduction of the l′-hydroxyl group and specificity for 2Z,4E-isomer. Conversion of the ethyl esters of (2Z,4E)- and (2E,4E)-l′-hydroxy-α-ionylideneacetates into the ethyl esters of both ABA and (2E,4E)-ABA demonstrated that ABA can be formed by oxidation of the 4′-position after the insertion of the 1′-hydroxy group. The ethyl 1′-hydroxy acids were also isomerized to the corresponding ethyl (2Z,4E)- and ethyl (2E,4E)-3′-hydroxy-β-ionylideneacetates. Ethyl (2Z,4E)-1′-hydroxy acid also gave small amounts of ethyl l′,4′-trans-diol of ABA. These results suggest that ABA may be formed through a (2Z,4E)-1′-hydroxy-α-ionylidene-type intermediate in addition to the previously proposed route through (2Z,4E)-4′-keto-α-ionylideneacetic acid.     

Methyl-substituted conformationally constrained rexinoid agonists for the retinoid X receptors demonstrate improved efficacy for cancer therapy and prevention

(2E,4E,6Z,8Z)-8-(3′,4′-Dihydro-1′(2H)-naphthalen-1′-ylidene)-3,7-dimethyl-2,3,6-octatrienoinic acid, 9cUAB30, is a selective rexinoid for the retinoid X nuclear receptors (RXR). 9cUAB30 displays substantial chemopreventive capacity with little toxicity and is being translated to the clinic as a novel cancer prevention agent. To improve on the potency of 9cUAB30, we synthesized 4-methyl analogs of 9cUAB30, which introduced chirality at the 4-position of the tetralone ring. The syntheses and biological evaluations of the racemic homolog and enantiomers are reported. We demonstrate that the S-enantiomer is the most potent and least toxic even though these enantiomers bind in a similar conformation in the ligand binding domain of RXR.     

A formyl peptide substituted with a conformationally constrained phenylalanine residue evokes a selective immune response in human neutrophils

Formyl-Met-Leu-Phe-OH (fMLP) binds to formyl peptide receptors, FPR1 and FPR2, and evokes migration and superoxide anion production in human neutrophils. To obtain a more effective and selective ligand, fMLP analogs in which the Phe residue was substituted with four isomers of cyclopropanephenylalanine were synthesized. While Z-isomer peptides induced both migration and superoxide anion production, E-isomer peptides elicited only chemotaxis. Homologous receptor desensitization experiments revealed that E-isomer peptides bound to FPR2. Although a selective agonist of chemotaxis also binds to FPR2 without increasing intracellular calcium concentration, E-isomer peptide elevated the concentration to the same level as fMLP. Understanding of mechanisms responsible for the selectivity of the reported selective agonists and ?Phe-substituted analogs should prove useful for revealing the relationship between receptor–ligand interactions and biological responses of human neutrophils.     

Conversion of (2Z,4E)-5-(1′,2′-epoxy-2′,6′,6′-trimethylcyclohexyl)-3-methyl-2,4-pentadienoic acid to xanthoxin acid by Cercospora cruenta, a fungus producing (+)-abscisic acid

(±)-(2Z,4E)-5-(1′,2′-epoxy-2′,6′,6′-trimethylcyclohexyl)-3-methyl-2,4-pentadienoic acid was metabolized by Cercospora cruenta, which has the ability to produce (+)-abscisic acid (ABA), to give (±)-(2Z,4E)-xanthoxin acid, (±)-(2Z,4E)-5′-hydroxy-1′,2′-epoxy-1′,2′-dihydro-β-ionylideneacetic acid, (±)-1′,2′-epoxy-1′,2′-dihydro-β-ionone and trace amounts of ABA.     

The E/Z isomerization step in the biosynthesis of Z-coniferyl alcohol in Fagus grandifolia

Beech bark contains significant amounts of Z-coniferyl and Z-sinapyl alcohols but not the corresponding E-isomers. There are a number of steps along the cinnamate pathway where E/Z isomerism of the cinnamyl double bond could occur. Studies of the conversion, in beech bark, of ¹⁴C-labelled E- and Z-ferulic acids, E-coniferylaldehyde and E- and Z-coniferyl alcohols indicate that this isomerism occurs at the level of the hydroxycinnamyl alcohols. This system differs, therefore, from that described for the isomerism of geraniol to nerol which proceeds via the corresponding aldehyde.     

Identification of the stereochemical requirements in the 4-aryl-2-cycloalkylidenhydrazinylthiazole scaffold for the design of selective human monoamine oxidase B inhibitors

Exploring the effect that substituents on the cycloaliphatic ring had on the inhibitory activity against human monoamine oxidase B of a series of 4-aryl-2-cycloalkylidenhydrazinylthiazoles led to the synthesis of a new series of 2-methylcyclopentyl and 3-methylcyclopentyl derivatives which were tested in vitro as mixtures of diastereoisomers. In fact, due to the presence of a chiral center on the cycloaliphatic ring and a trisubstituted CN bond, they exist as four diastereoisomers ((E)-(R), (E)-(S), (Z)-(R), (Z)-(S)). 4-(2,4-Difluorophenyl)-2-(2-(3-methylcyclopentylidene)hydrazinyl)thiazole was chosen as a model to investigate the influence of stereochemical requirements on the inhibitory activity against hMAO-B of these derivatives after a stereoconservative synthesis and semi-preparative HPLC diastereoseparation. (R)-(Z) isomer of this compound was endowed with a potent and selective hMAO-B inhibition higher than that of reference drugs as also corroborated by molecular modeling studies.     

Preparation of novel (Z)-4-ylidenebenzo[b]furo[3,2-d][1,3]oxazines and their biological activity

A reaction of 2-acetyl-3-acylaminobenzo[b]furans (9d–o) with Vilsmeier (VM) reagent afforded a mixture of (E)- and (Z)-{(E)-2-aralkenylbenzo[b]furo[3,2-d][1,3]oxazin-4-ylidene}acetaldehydes (5) with a characteristic exo-formylmethylene group on the oxazine ring. The Z-isomer was more stable than the E-isomer. The Z-isomers ((Z)-5) were reacted with phosphonate reagents under two different conditions to obtain various butadiene derivatives (12) containing benzo[b]furo[3,2-d][1,3]oxazine skeleton. Typical compounds (5 and 12) were evaluated for their anti-osteoclastic bone resorption activity, antagonistic activity for the cysLT1 receptor and growth inhibitory activity for MIA PaCa-2 and MCF-7. Compounds 12f and 12j showed potent anti-osteoclastic bone resorption activity comparable to E₂ (17β-estradiol).     

Full characterization of PDX, a neuroprotectin/protectin D1 isomer, which inhibits blood platelet aggregation

Our study aimed to establish the complete structure of the main dihydroxy conjugated triene issued from the lipoxygenation (soybean enzyme) of docosahexaenoic acid, named PDX, an isomer of protectin/neuroprotectin D1 (PD1/NPD1) described by Bazan and Serhan. NMR approaches and other chemical characterization (e.g. GC-MS, HPLC and LC-MS/MS) indicated that PDX is 10(S),17(S)-dihydroxy-docosahexa-4Z,7Z,11E,13Z,15E,19Z-enoic acid. The use of ¹⁸O₂ and mass spectrometry showed that PDX is a double lipoxygenation product. Its structure differs from PD1, with E,Z,E geometry (PDX) instead of E,E,Z (PD1) and S configuration at carbon 10 instead of R. PDX inhibits human blood platelet aggregation at sub-micromolar concentrations.     

2-Fluoro and 2-Methoxycarbonyl Epoxy-β-ionylideneacetic Acids as Abscisic Acid Analogs

Abscisic acid (ABA) is easily isomerized to inactive trans-ABA by light. To solve this problem, two variations of epoxy-?-ionylideneacetic acid were synthesized as ABA analogs, each of them having a methoxycarbonyl or a fluoric substituent at the 2-position. The 2E-, and 2Z-fluorinated analogs showed moderate growth inhibitory activity toward rice seedlings and lettuce seeds, whereas the methoxycarbonyl analog was inactive toward rice seedling growth and only partially active toward lettuce germination. The 2E-fluorinated analog was extensively isomerized to the 2Z-isomer by UV irradiation. We think that a steric requisite for the 2E-position was high, and that the fluorine substituent was not effective for fixing the 2-double bond in the E-configuration.     

Correlation between loss of pro-chiral hydrogen and E,Z geometry in isoprenoid biosynthesis

Biosynthesis of several mono- and sesqui-terpenes that possess E or Z double bonds, or which are generally considered to be derived from precursors possessing such geometries, involved loss of the pro-4S hydrogen of mevalonate in the construction of the double bond. These results confirm and extend previous observations. A recent claim to have newly discovered such a stereochemical correlation is rejected.     

Synthesis and Biological Activity of Methyl 3-Demethyl-Abscisate and Its Related Analogs

To elucidate the role of the methyl substituent on the side chain of abscisic acid (ABA), we synthesized (2Z,4E)-3-demethyl-α-ionylideneacetic acid (4) and its related analogs, methyl (2Z)-3-demethyl-β-ionylideneacetate 1′,2′-epoxide (9) and methyl (2Z) and (2E)-3-demethyl-abscisate (12) and (13). The biological assay of these compounds suggested that the 3-methyl group on the side chain of ABA was indispensable to biological activity.     

(5Z, 7E)-5,7-Dodecadien-1-ol: Female Sex Pheromone of the Pine Moth Dendrolimus spectabilis Butler

The sex pheromone of the pine moth Dendrolimus spectabilis Butler was tentatively identified as 5,7-dodecadien-l-ol by the use of the electroantennogram technique. Analyses of abdominal tip extracts of virgin females by gas-liquid chromatography and mass spectroscopy showed the presence of a (5Z, 7E)-isomer and a (5E, 7E)-isomer in the ratio of about ca. 5:1. In field examinations with four synthetic isomers of 5,7-dodecadien-l-ol, only traps baited with the (5Z, 7E)-isomer captured an appreciable numbers of male moths.     

Gene modulation by the cyclooxygenase inhibitor,sulindac sulfide,in human colorectal carcinoma cells: possible link to apoptosis

The mechanisms underlying the anti-tumorigenic properties of cyclooxygenase inhibitors are not well understood. One novel hypothesis is alterations in gene expression. To test this hypothesis sulindac sulfide, which is used to treat familial adenomatous polyposis, was selected to detect gene modulation in human colorectal cells at physiological concentrations with microarray analysis. At micromolar concentrations, sulindac sulfide stimulated apoptosis and inhibited the growth of colorectal cancer cells on soft agar. Sulindac sulfide (10 microm) altered the expression of 65 genes in SW-480 colorectal cancer cells, which express cyclooxygenase-1 but little cyclooxygenase-2. A more detailed study of 11 genes revealed that their expression was altered in a time- and dose-dependent manner as measured by real-time RT-PCR. Northern analysis confirmed the expression of 9 of these genes, and Western analysis supported the conclusion that sulindac sulfide altered the expression of these proteins. Cyclooxygenase-deficient HCT-116 cells were more responsive to sulindac sulfide-induced gene expression than SW-480 cells. However, this response was diminished in HCT-116 cells overexpressing cyclooxygenase-1 compared with normal HCT-116 cells suggesting the presence of cyclooxygenase attenuates this response. However, prostaglandin E2, the main product of cyclooxygenase, only suppressed the sulindac sulfide-induced expression of two genes, with little known biological function while it modulated the expression of two more. The most likely explanation for this finding is the metabolism of sulindac sulfide to inactive metabolites by the peroxidase activity of cyclooxygenase. In conclusion, this is the first report showing sulindac sulfide, independent of cyclooxygenase, altered the expression of several genes possibly linked to its anti-tumorigenic and pro-apoptotic activity.     

Isolation and Photoisomerization of a New Anthraquinone from Hairy Root Cultures of Sesamum indicum

An unstable anthraquinone was isolated from hairy root cultures of Sesamum indicum after preventing light throughout all experimental procedures. The structure of the (Z)-isomer of a previously isolated anthraquinone was determined to be 2-[(Z)-4-methylpenta-1,3-dien-1-yl]anthraquinone by spectroscopic methods. This compound was readily isomerized to the known (E)-isomer under light.     

Anti-AIDS agents 84. Synthesis and anti-human immunodeficiency virus (HIV) activity of 2′-monomethyl-4-methyl- and 1′-thia-4-methyl-(3′R,4′R)-3′,4′-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) analogs

In a continuing investigation into the pharmacophores and structure–activity relationship (SAR) of (3′R,4′R)-3′,4′-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) as a potent anti-HIV agent, 2′-monomethyl substituted 1′-oxa, 1′-thia, 1′-sulfoxide, and 1′-sulfone analogs were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. Among them, 2′S-monomethyl-4-methyl DCK (5a)³ and 2′S-monomethyl-1′-thia-4-methyl DCK (7a) exhibited potent anti-HIV activity with EC₅₀ values of 40.2 and 39.1 nM and remarkable therapeutic indexes of 705 and 1000, respectively, which were better than those of the lead compound DCK in the same assay. In contrast, the corresponding isomeric 2′R-monomethyl-4-methyl DCK (6) and 2′R-monomethyl-1′-thia-4-methyl DCK (8) showed much weaker inhibitory activity against HIV-1 replication. Therefore, the bioassay results suggest that the spatial orientation of the 2′-methyl group in DCK analogs can have important effects on anti-HIV activity of this compound class.     

A novel acylphloroglucinol from the brown alga Zonaria tournefortii

A novel acylphloroglucinol, (5Z,8Z11Z,13E,17Z)-2′-eicosa-15(S)-hydroxy-5,8,11,13,17-pentaenoylphloroglucinol, has been isolated from the brown alga Zonaria tournefortii and its structure proved by spectroscopic and chemical methods.     

Synthesis of 2′-C-α-Methyl-2′,3′-dideoxynucleosides

Abstract

A general method for the synthesis of 2′-C-α-methyl-2′,3′-dideoxynucleosides is presented. Stereofacial selectivity of the 2-C-methylation reaction of γ-lactone has been investigated, in which the presence of a bulky group at the 5-hydroxymethyl produced the α-isomer as a major product. During glycosylation, the α-methyl group directed the formation of nucleosides in favor of the ß-isomer. This methodology is applied to the synthesis of some new pyrimidine and purine nucleosides.

     

Design,synthesis, and X-ray crystal structures of 2,4-diaminofuro[2,3-d]pyrimidines as multireceptor tyrosine kinase and dihydrofolate reductase inhibitors

To optimize dual receptor tyrosine kinase (RTK) and dihydrofolate reductase (DHFR) inhibition, the E- and Z-isomers of 5-[2-(2-methoxyphenyl)prop-1-en-1-yl]furo[2,3-d]pyrimidine-2,4-diamines (1a and 1b) were separated by HPLC and the X-ray crystal structures (2.0 and 1.4 Å, respectively) with mouse DHFR and NADPH as well as 1b with human DHFR (1.5 Å) were determined. The E- and Z-isomers adopt different binding modes when bound to mouse DHFR. A series of 2,4-diaminofuro[2,3-d]pyrimidines 2–13 were designed and synthesized using the X-ray crystal structures of 1a and 1b with DHFR to increase their DHFR inhibitory activity. Wittig reactions of appropriate 2-methoxyphenyl ketones with 2,4-diamino-6-chloromethyl furo[2,3-d]pyrimidine afforded the C8–C9 unsaturated compounds 2–7 and catalytic reduction gave the saturated 8–13. Homologation of the C9-methyl analog maintains DHFR inhibitory activity. In addition, inhibition of EGFR and PDGFR-β were discovered for saturated C9-homologated analogs 9 and 10 that were absent in the saturated C9-methyl analogs.     

A facile E,Z-isomerization of α,β-unsaturated terpenoid lactones and its effect on plant growth activity

Various synthetic C-16 lactones prepared in earlier work are the Z-isomers. These have been isomerized chemically to the corresponding E-isomers. It is observed that these isomers have different root initiating properties, which reflect the significance of the geometry of double bonds in conjugated γ-lactones which act as plant growth regulators.