Studies on griseolic acid derivatives. I. Synthesis of substituted derivatives of griseolic acid at the N1, C6, C2' or C7' position and their biological activities

Griseolic acid derivatives having a different substituent at the N1,C6,C2' or C7' position of the natural product were synthesized and their structure activity relationship to cyclic nucleotide phosphodiesterase inhibitory activity was investigated.     

2beta,3beta-Difluorosialic acid derivatives structurally modified at the C-4 position: synthesis and biological evaluation as inhibitors of human parainfluenza virus type 1

A series of 4-O-substituted 2beta,3beta-difluorosialic acid derivatives (3a-d) has been synthesized. A key intermediate was synthesized efficiently by the electrophilic syn-addition of fluorine to the double bond of a glycal precursor using molecular fluorine or xenon difluoride in the presence of BF(3).OEt(2). Among compounds 3a-d, the 4-O-thiocarbamoylmethyl derivative 3c showed the most potent inhibitory activity against sialidase of human parainfluenza virus type 1. [structure: see text].     

The novel pyrimidine and purine derivatives of l-ascorbic acid: synthesis, one- and two-dimensional 1H and 13C NMR study, cytostatic and antiviral evaluation

The syntheses of the novel C-5 substituted pyrimidine derivatives of l-ascorbic acid containing free hydroxy groups at C-2' (6-10) or C-2' and C-3' (11-15) positions of the lactone ring are described. Debenzylation of the 6-chloro- and 6-(N-pyrrolyl)purine derivatives of 2,3-O,O-dibenzyl-l-ascorbic acid (16 and 17) gave the new compounds containing hydroxy groups at C-2' (18) and C-2' and C-3' (19 and 20). Z- and E-configuration of the C4'C5' double bond and position of the lactone ring of the compounds 6-9 were deduced from their one- and two-dimensional (1)H and (13)C NMR spectra and connectivities in NOESY and HMBC spectra. Compounds 15 and 18 showed the best inhibitory activities of all evaluated compounds in the series. The compound 15 containing 5-(trifluoromethyl)uracil showed marked inhibitory activity against all human malignant cell lines (IC(50): 5.6-12.8 microM) except on human T-lymphocytes. Besides, this compound influenced the cell cycle by increasing the cell population in G2/M phase and induced apoptosis in SW 620 and MiaPaCa-2 cells. The compound 18 containing 6-chloropurine ring expressed the most pronounced inhibitory activities against HeLa (IC(50): 6.8 microM) and MiaPaCa-2 cells (IC(50): 6.5 microM). The compound 20 with 6-(N-pyrrolyl)purine moiety showed the best differential inhibitory effect against MCF-7 cells (IC(50): 35.9 microM).     

Inhibition of hepatic stearoyl-CoA desaturase activity by trans-10, cis-12 conjugated linoleic acid and its derivatives

Conjugated linoleic acid (CLA) has been reported to decrease stearoyl-CoA desaturase (SCD) activity by decreasing mRNA expression. This investigation was designed to determine whether structurally related compounds of CLA have a direct inhibitory effect on SCD activity. Trans-10,cis-12 CLA had strong inhibitory activity on SCD while cis-9,trans-11, and trans-9,trans-11 isomers had no effect. Trans-10 octadecenoate was not inhibitory, whereas cis-12 octadecenate was inhibitory, but not as effective as trans-10,cis-12 CLA. Of the oxygenated derivatives, 9-peroxy-cis/trans-10, trans-12 octadecadienoate was a more effective inhibitor than trans-10,cis-12 CLA, whereas 9-hydroxy-trans-10, cis-12 octadecadienoate was less effective. Interestingly, cis-11 octadecadienoate and cis-12 octadecen-10-ynoate were slightly inhibitory. However, trans-9 and trans-11 octadecenoates, and trans-9,cis-12 octadecadienoate were all inactive under test condition, as were linoleate, oleate, and arachidonate. Derivatives of CLA acid modified to alcohol, amide or chloride were all inactive. A cis-12 double bond appears to be a key structural feature for inhibiting SCD activity, especially when coupled with a trans-10 double, whereas a cis-11 double bond is less effective.     

Synthesis of both enantiomers of hydroxypipecolic acid derivatives equivalent to 5-azapyranuronic acids and evaluation of their inhibitory activities against glycosidases

We have synthesized 3-hydroxy- and 3,4,5-trihydroxypipecolic acid derivatives corresponding to 5-aza derivatives of uronic acids and evaluated their inhibitory activities against various glycosidases including beta-glucuronidase. Compounds 4 and 5 were chosen as common intermediates for the synthesis of 3,4,5-trihydroxypipecolic acids and 3-hydroxypipecolic acids as well as for 3-hydroxybaikiain, a unique natural product isolated from a toxic mushroom. Cross aldol reaction of N-Boc-allylglycine derivative with acrolein followed by the ring-closing metathesis gave 4 and 5 as a mixture of diastereomers which could be separated by silica gel column chromatography. By employing lipase-catalyzed kinetic resolution, the synthesis of both L- and D-isomers of 3,4,5-trihydroxy- and 3-hydroxypipecolic acids was achieved. None of the compounds tested showed inhibitory activity against alpha- and beta-glucosidases. On the other hand, L-23 and L-29 were found to have potent inhibitory activity against beta-glucuronidase. In addition, it is interesting that some uronic-type azasugar derivatives showed moderate inhibitory activities against beta-N-acetylglucosaminidase.     

Ascotoxin (Decumbin), a Metabolite of Ascochyta imperfecta PECK.

From the mycelium of Ascochyta imperfecta decumbin, C₁₆H₂₄O₄, mp 203°C, was obtained in one percent yield.

The absolute structure of decumbin was presented as [II] by the following evidences: The configuration about C₄ was determined as (S) by the benzoate rule on the tetrahydromonoketone (21). The hydroxyl at C₇ is α, because tetrahydrodecumbin (23) showed no intramolecular hydrogen bond, while its C₇ epimer (24) did. Ring juncture was determined by ORD of a five membered ketone (16). Two double bonds were found to be trans from IR data. The stereochemistry of decumbin monoepoxide (7), tetrahydropyrans (12 and 13) was also studied. Plant tests of the twenty derivatives of decumbin on lucerne and rape revealed that the growth inhibition activity has close relation with the presence of double bond in the thirteen membered lactone ring.     

Synthesis and inhibitory activity of benzoic acid and pyridine derivatives on influenza neuraminidase

Based upon the activity and X-ray crystallographic studies of tri-substituted benzene derivatives containing carboxylic acid, acetamido and guanidine groups, we investigated the effect of the fourth substituent to fulfill the fourth pocket of neuraminidase enzyme. The groups selected as fourth substituents were hydroxymethyl, hydroxyethyl, oxime and amino. These tetra-substituted benzene derivatives were synthesized and evaluated for neuraminidase inhibitory activity. All these compounds were found to have poorer IC(50) values than the tri-substituted compounds. Further, benzene ring was replaced by pyridine ring and di, tri and tetra-substituted pyridine derivatives were synthesized. The activity of the pyridine derivatives was comparable to benzene derivatives. The fourth substituent seems to disturb the binding of the other three substituents, so the activity is reduced as compared to tri-substituted benzene and pyridine derivatives.     

Synthesis of sialic acid derivatives having a CC double bond substituted at the C-5 position and their glycopolymers

Glycomonomers of sialic acid in which the acetamide group at C-5 was converted into two kinds of CC double bond substituents were prepared and the fully protected glycomonomers were directly polymerized before deprotection steps. Radical polymerization with acrylamide in DMF in the presence of ammonium persulfate and N,N,N’,N’-tetramethylethylenediamine proceeded smoothly and gave corresponding sialopolymers. Interestingly glycomonomers had hemagglutination inhibitory activities not only for H1N1 but also for H3N2 of human influenza virus strains.     

Novel 4,1-benzoxazepine derivatives with potent squalene synthase inhibitory activities.

A series of (3,5-trans)-2-oxo-5-phenyl-1,2,3,5-tetrahydro-4,1-benzoxazepine derivatives were synthesized and evaluated for squalene synthase inhibitory and cholesterol biosynthesis inhibitory activities. Through modification of substituents of the lead compounds 1a and 1b, it was found that 4,1-benzoxazepine-3-acetic acid derivatives with isobutyl and neopentyl groups at the 1-position, the chloro atom at the 7-position, and the chloro and methoxy groups at the 2'-position on the 5-phenyl ring, had potent squalene synthase inhibitory activity. Among such compounds, the 5-(2,3-dimethoxyphenyl) derivative 2t exhibited potent inhibition of cholesterol biosynthesis in HepG2 cells. As a result of optical resolution study of 2t, the absolute stereochemistry required for inhibitory activity was determined to be 3R,5S. In vivo study showed that the sodium salt of (3R,5S)-7-chloro-5-(2,3-dimethoxyphenyl)-1-neopentyl-2-oxo-1,2,3,5-tetrahydro-4,1-benzoxazepine-3-acetic acid 20 effectively reduced plasma cholesterol in marmosets.     

Key structural features of cis-cinnamic acid as an allelochemical

1-O-cis-cinnamoyl-β-d-glucopyranose is one of the most potent allelochemicals isolated from Spiraea thunbergii Sieb. It is suggested that it derives its strong inhibitory activity from cis-cinnamic acid, which is crucial for phytotoxicity. It was synthesized to confirm its structure and bioactivity, and also a series of cis-cinnamic acid analogues were prepared to elucidate the key features of cis-cinnamic acid for lettuce root growth inhibition. The cis-cyclopropyl analogue showed potent inhibitory activity while the saturated and alkyne analogues proved to be inactive, demonstrating the importance of the cis-double bond. Moreover, the aromatic ring could not be replaced with a saturated ring. However, the 1,3-dienylcyclohexene analogue showed strong activity. These results suggest that the geometry of the C–C double bond between the carboxyl group and the aromatic ring is essential for potent inhibitory activity. In addition, using several light sources, the photostability of the cinnamic acid derivatives and the role of the C–C double bond were also investigated.     

17,20-lyase inhibitors. Part 4: design, synthesis and structure-activity relationships of naphthylmethylimidazole derivatives as novel 17,20-lyase inhibitors

A novel series of naphthylmethylimidazole derivatives and related compounds have been investigated as selective 17,20-lyase inhibitors. Optimization of the substituent at the 6-position on the naphthalene ring was performed to yield a methylcarbamoyl derivative, which exhibited potent inhibitory activity against human 17,20-lyase and promising selectivity (>200-fold) for 17,20-lyase over CYP3A4. Further modifications of the methylcarbamoyl derivative led to the discovery of the corresponding tricyclic compound, which showed highly potent activity against human 17,20-lyase (IC(50) 19 nM) and good selectivity (>1000-fold) for inhibition of 17,20-lyase over CYP3A4. Additional biological evaluation revealed that the tricyclic compound had potent in vivo efficacy in monkeys and favorable pharmacokinetic profiles when administered in rats. Asymmetric synthesis of the selective tricyclic inhibitor was also achieved using a chiral α-hydroxy ketone.     

Synthesis, structural studies, and cytostatic evaluation of 5,6-di-O-modified L-ascorbic acid derivatives

The 5,6-di-O-tosylated derivative of l-ascorbic acid was synthesized by selective protection and deprotection of 2,3- and 5,6-dihydroxy functional groups involving 5,6-ditosylation in the final step, while the novel 6-acetoxy, 6-hydroxy, and 6-chloro derivatives of 4,5-didehydro-l-ascorbic acid were obtained by reaction of ditosylated compound with nucleophilic reagents. The analysis of 3JH-4-H-5 homonuclear coupling constants shows that all l-ascorbic acid derivatives except for epoxy and 4,5-didehydro compounds exist in high population as gauche conformers across C-4-C-5 bonds, while 3JC-3-H-5 heteronuclear coupling constants in 4,5-didehydro derivatives indicate cis geometry along C-4-C-5 double bond. The X-ray crystal structure analysis of 2,3-di-O-benzyl-5,6-epoxy- and 5,6-isopropylidene-l-ascorbic acid shows that the oxygen atoms attached at positions 2 and 3 of the lactone ring are disposed in a synperiplanar fashion. Besides that, the dioxolane ring adopts half-chair conformation. The molecules of epoxy derivative are joined into infinite chains by one weak hydrogen bond of C-H...O type. Two O-H...O, and C-H...O hydrogen bonds link the molecules of 5,6-di-O-isopropylidene compound into two-dimensional network. 6-Chloro derivative of 2,3-di-O-benzyl-l-ascorbic acid showed the best cytostatic effects against all tested malignant tumor cells (IC50: approximately 18 microM).     

Inhibition of phenylalanine ammonia-lyase by cinnamic acid derivatives and related compounds

Thirty-five derivatives of cinnamic acid and related compounds were tested for inhibition against phenylalanine ammonia-lyase (PAL) derived from sweet potato, pea and yeast. Caffeic and gallic acids showed inhibition against PAL originating from higher plants, but not against yeast PAL. In contrast, yeast PAL was specifically inhibited by p-hydroxycinnamic and p-hydroxybenzoic acids. The results suggest that caffeic and gallic acids may act as regulatory substances in phenylpropanoid metabolism in higher plants. Inhibition experiments with synthetic cinnamic acid derivatives have revealed that the presence of a hydrophobic aromatic ring, α,β-double bond and carboxyl group is essential for inhibitory activity. 2-Naphthoic acid which fulfills these structural requirements showed a strong inhibition. The size and shape of the active site is discussed from structure-activity relationships of cinnamic acid derivatives. o-Chlorocinnamic acid, one of the strongest inhibitors found in this study showed an inhibitory effect on the growth of the roots of rice seedlings.     

Bioactivity studies of oxysporone and several derivatives

Recently oxysporone, a phytotoxic dihydrofuropyranone, was isolated along with two closely related compounds, afritoxinones A and B, from liquid cultures of Diplodia africana, an invasive fungal pathogen of Phoenicean juniper. In this study, eight derivatives were hemisynthesized and assayed for their phytotoxic and antifungal activities in comparison to the parent compound. Each compound was tested on non-host plants and on four destructive plant pathogens such as Athelia rolfsii, Diplodia corticola, Phytophthora cinnamomi and P. plurivora. The results on the phytotoxic activity showed that the dihydrofuropyranone carbon skeleton and both the double bond the hydroxy group of dihydropyran ring appeared to be structural features important in conferring activity. Although the data concerning the antifungal activity did not allow to extract any structure–activity relationships, it should be underlined that the conversion of oxysporone into the corresponding 4-O-benzoyl derivative led to a compound showing a good antifungal activity towards three out of the four organisms tested.     

Purification and characterization of N-ethylmaleimide reducing enzyme from Candida lipolytica

N-Ethylmaleimide (NEM) reducing enzyme was purified to homogeneity from cell-free extracts of Candida lipolytica by chromatography techniques. The molecular weight of the native enzyme was estimated to be about 43,000 by gel filtration using Superose 12 and to be 47,000 by SDS-PAGE. This enzyme can use both NADPH and NADH as an electron donor, and catalyzes the reduction of the carbon-carbon double bond of five membered ring compounds which have two conjugated carbonyl groups on both sides of a double bond.     

Synthesis,crystal structure and biological evaluation of new phosphoramide derivatives as urease inhibitors using docking,QSAR and kinetic studies

In an attempt to achieve a new class of phosphoramide inhibitors with high potency and resistance to the hydrolysis process against urease enzyme, we synthesized a series of bisphosphoramide derivatives (01–43) and characterized them by various spectroscopic techniques. The crystal structures of compounds 22 and 26 were investigated using X-ray crystallography. The inhibitory activities of the compounds were evaluated against the jack bean urease and were compared to monophosphoramide derivatives and other known standard inhibitors. The compounds containing aromatic amines and their substituted derivatives exhibited very high inhibitory activity in the range of IC₅₀ = 3.4–1.91 × 10⁻¹⁰ nM compared with monophosphoramides, thiourea, and acetohydroxamic acid. It was also found that derivatives with PO functional groups have higher anti-urease activity than those with PS functional groups. Kinetics and docking studies were carried out to explore the binding mechanism that showed these compounds follow a mixed-type mechanism and, due to their extended structures, can cover the entire binding pocket of the enzyme, reducing the formation of the enzyme-substrate complex. The quantitative structure-activity relationship (QSAR) analysis also revealed that the interaction between the enzyme and inhibitor is significantly influenced by aromatic rings and PO functional groups. Collectively, the data obtained from experimental and theoretical studies indicated that these compounds can be developed as appropriate candidates for urease inhibitors in this field.     

Synthesis and antimycobacterial evaluation of new trans-cinnamic acid hydrazide derivatives

In this work, we report the synthesis and the antimycobacterial evaluation of new trans-cinnamic acid derivatives of isonicotinic acid series (5) and benzoic acid series (6), designed by exploring the molecular hybridization approach between isoniazid (1) and trans-cinnamic acid derivative (3). The minimum inhibitory concentration (MIC) of the compounds 5a-d and 6c exhibited activity between 3.12 and 12.5 microg/mL and could be a good start point to find new lead compounds against multi-drug resistant tuberculosis.     

A new class of salicylic acid derivatives for inhibiting YopH of Yersinia pestis

Previously, we identified a class of salicylic acid derivatives that display inhibitory activity against the protein tyrosine phosphatase YopH from Yersinia pestis. Because docking study suggested that the large phenyl ring attaching to the salicylic acid core might be exposed to the solvent and might not contribute significantly to binding, we have developed a new class of compounds that no longer contain this phenyl ring. We first devised a synthetic scheme for the compounds and then developed an automated computational screening model surrounding this synthetic scheme to help select a small number of compounds for synthesis and experimental testing. Based on this computational screening model and the analysis of the structure–activity relationship of our previous class of compounds, we have synthesized eight compounds and found five that yield micromolar activity. When applying in a larger scale, the synthetic scheme and the computational screening model developed here should help to identify even more potent inhibitors in the future.     

Novel marine flagellate fatty acid: structural elucidation by GC-MS analysis of DMOX derivatives and DMDS adducts.

In situ biodegradation experiments of marine particles were performed in deep Atlantic waters. Lipid changes were associated with the colonization of the decaying detritus by marine flagellates smaller than 10 microm in size. Fatty acid methyl esters (FAMEs) of these flagellates showed high proportion of a FAME with a molecular weight (MW) of 320. Its structure could not be unambiguously resolved by retention times on gas chromatography runs using polar and nonpolar columns, nor by routine gas chromatography coupled to mass spectrometry (GC-MS). Complementary GC-MS analysis of two types of derivatives was performed to fully elucidate the structure of this novel acid. GC-MS analysis of 4,4-dimethyloxazoline (DMOX) derivative of the compound enabled localization of a double bond in position Delta17, whereas other double bond locations could not be unambiguously located by spectrum interpretation. DMDS addition on the flagellate biomarker produced monocyclic triadducts. Fragment suites corresponding to gradual losses of thiomethyl substituents indicated the presence of a five-membered thioether cycle, located on the methyl side of the derivative. Fragment suites produced by cleavage of C linked to sulfured substituents revealed various possible structures. However, interpretation of the spectra in relation with the fragmentation of the DMOX derivative yielded a convergent identification of the flagellate biomarker, as a non-methylene-interrupted C20:3Delta7,13,17 FAME.     

Structure-Activity Correlations with Compounds Related to Abscisic Acid

Inhibition of cell expansion of excised embryonic axes of Phaseolus vulgaris was used to evaluate the growth-inhibiting activity of abscisic acid and related compounds. None of the 13 compounds tested was as active as abscisic acid. 4-Hydroxyisophorone, a substance representative of the abscisic acid ring system was essentially inactive; cis, trans-3-methylsorbic acid, a compound resembling the side chain of abscisic acid, had low activity; and cis, trans-beta-ionylideneacetic acid was one-sixth as active. Loss of the ring double bond results in a drastic decrease in biological activity. Comparison of our results with those reported previously leads to the suggestion that the double bond of the cyclohexyl moiety may have an important function in determining the degree of activity of cis, trans-ionylideneacetic acids. Two modes of action are discussed. It seems possible that the ring double bond is involved in covalent bonding in binding of the abscisic acid analogue to macromolecules. This may require formation of an intermediate epoxide. It can also be argued that stereochemical differences between cyclohexane derivatives are important factors in determining the degree of biological activity.