Enzymatic synthesis of cyclopeptine intermediates in Penicillium cyclopium

Cyclopeptine, a benzodiazepine alkaloid of Penicillium cyclopium, is formed from anthranilic acid, L-phenylalanine and the methyl group of L-methionine by cyclopeptine synthetase. The following partial activities of this enzyme system were determined in vitro: anthranilic acid and L-phenylalanine adenylyltransferase activity, binding of anthranilic acid and L-phenylalanine as thioesters to proteins, formation of thioester-bound N-methyl-L-phenylalanine and N-methyl-L-phenylalanylanthranilic acid. The obtained results indicate that cyclopeptine is formed via enzyme-bound intermediates by the thiotemplate mechanism of peptide biosynthesis.     

A Molecular Electrostatic Potential Mapping Study of Some Fluoroquinolone Anti-Bacterial Agents

Molecular electrostatic potential (MEP) maps of some fluoroquinolones having varying degrees of activity against the bacterium Staphylococcus Aureus have been studied using the optimized hybridization displacement charges (HDC) combined with Löwdin charges obtained by the AM1 method. The roles of different substitutions at the N₁-position in the parent quinolone ring have been studied. The conformation of the carboxylic group attached to the quinolone ring was shown to be such that there is an intramolecular hydrogen bonding between the hydrogen atom of this group and the oxygen atom of the carbonyl group of the quinolone moiety. The carbonyl oxygen atom of the quinolone moiety, hydroxyl oxygen atom of the carboxylic group and the terminal nitrogen atom of the piperazin ring attached to the quinolone ring appear to be involved in the action of the drugs through electrostatic interactions while the N₁-alkyl substituents seem to be involved in the same through hydrophobic interactions.     

Biosynthesis of podophyllum lignans—i. cinnamic acid precursors of podophyllotoxin in podophyllum hexandrum

Feeding experiments in Podophyllum hexandrum plants have established that phenylalanine, cinnamic acid and ferulic acid are good precursors of the two major aryltetralin lignans podophyllotoxin and 4′-demethylpodophyllotoxin. Sinapic and 3,4,5-trimethoxycinnamic acids were poorly utilized, showing that the substitution pattern of the pendent aryl ring is built up after coupling of the two phenylpropane units. Degradation studies on podophyllotoxin derived from [3-O¹⁴CH₃] ferulic acid show that the two halves of the lignan molecule are equally labelled supporting a biosynthetic sequence involving oxidative coupling of two similar phenylpropane precursors having the substitution pattern of ferulic acid. Although 3,4-methylenedioxycinnamic acid was readily incorporated, degradative studies prove that this compound is not incorporated intact, but via a metabolic sequence in which the methylenedioxy carbon atom enters the C₁-pool and then labels the methylenedioxy and methoxyl substituents of podophyllotoxin. The rest of the skeleton is incorporated via ferulic acid, presumably by way of caffeic acid.     

Alantrypinone and its derivatives: Synthesis and antagonist activity toward insect GABA receptors

The γ-aminobutyric acid (GABA) receptor bears important sites of action for insecticides. Alantrypinone is an insecticidal alkaloid that acts as a selective antagonist for housefly (vs rat) GABA receptors, and is considered to be a lead compound for the development of a safer insecticide. In an attempt to obtain compounds with greater activity, a series of racemic alantrypinone derivatives were systematically synthesized using hetero Diels–Alder reactions, and a total of 34 compounds were examined for their ability to inhibit the specific binding of [³H]4′-ethynyl-4-n-propylbicycloorthobenzoate, a high-affinity non-competitive antagonist, to housefly-head membranes. The assay results showed that (1) there is no significant difference between the potencies of natural (+)-alantrypinone and its synthetic racemate; (2) the amide NHs at the 2- and 18-positions are important for high activity; (3) there is a considerable drop in potency for compounds without an aromatic ring at the 16-position; and (4) a large substituent at the 3-position is detrimental to high activity.     

Correlation of carboxylic acid pKa to protein binding and antibacterial activity of a novel class of bacterial translation inhibitors

Previously we reported the discovery and initial optimization of a novel anthranilic acid derived class of antibacterial agents which suffered from extensive protein binding. This report describes efforts directed toward understanding the relationship of the acidity of the carboxylic acid with the extent of protein binding. The pK(a) of the acid was modified via the synthesis of a number of anthranilic acid analogs which vary the aromatic ring substituent at the 4-position. The pK(a) and HSA binding constants have been determined for each of the analogs. Our results indicate a correlation between pK(a) and HSA K(d). The physical properties and antibacterial activities will be discussed as well as how these results help address the protein binding issue with this series of compounds.     

Pleiotropic effect of a pelargonidin-hydroxylation gene in Silene dioica?

In petals of Silene dioica a gene P has been identified, which controls the 3′-hydroxylation of the B-ring of pelargonidin to cyanidin. Another gene Ac controls the acylation of the terminal sugar at the 3-position of anthocyanin 3-rhamnosylglucoside-5-glucosides. In p/p plants the bound acyl group is p-coumaric acid; in P/P plants, however, it is caffeic acid. Gene P seems to exert a pleiotropic effect: it not only controls the hydroxylation of the B-ring of pelargonidin but also that of the acyl group.     

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.     

Exploration of the 5-bromopyrimidin-4(3H)-ones as potent inhibitors of PDE5

The substituents both at the 6-position of the 5-bromopyrimidinone ring and at the 5′-position of the phenyl ring of 5-bromopyrimidin-4(3H)-ones were explored. 5-Bromo-6-isopropyl-2-(2-propoxy-phenyl)pyrimidin-4(3H)-one was identified as a new scaffold for potent PDE5 inhibitors. The crystal structures of PDE5/2e and PDE5/10a complexes provided a structural basis for the inhibition of 5-bromopyrimidinones to PDE5. In addition, it was also found that there is a great tolerance for the substitution at the 5′-position of the phenyl ring of 5-bormopyrimidinones and the resulted compound 13a has the highest inhibition activity to PDE5 (IC₅₀, 1.7 nM).     

Cyclopeptide alkaloids from Melochia corchorifolia

Adouetine-y′ and a new cyclopeptide alkaloid, melofoline, have been isolated from melochia corchorifolia. The latter was characterized mainly from its mass spectrum and hydrolysis products. Melofoline has N,N-dimethyl-β-hydroxyleucine as the terminal amino acid and 2-aminobutyric acid as the ring amino acid, neither of which has been found in the positions before.     

Cinnamic acid intermediates as precursors to mesembrine and some observations on the late stages in the biosynthesis of the mesembrine alkaloids

Experiments with various labelled cinnamic acid derivatives establish, in conjunction with previous work, that the incorporation of phenylalanine into the 3a-aryl octahydroindole ring system of the mesembrine alkaloids occurs via the intermediacy of cinnamic acid and 4′-hydroxycinnamic acid. The major pathway to the 3′,4′-di-oxyaryl substituted alkaloids proceeds via 4′-hydroxydihydrocinnamic acid (4′-phloretic acid), and 3′4′-dioxy-genated cinnamic acids are not involved as intermediates on this major pathway. In accord with this latter finding, the 3′-aryl oxygen substituent is introduced at a late state in the biosynthesis as evidenced by the bioconversion in S. strictum of sceletenone to mesembrenol and other related alkaloids. The late stages in the biosynthesis of the alkaloids are shown to involve the sequence: sceletenone, 4′-O-demethylmesembrenone, mesembrenone. Mesembrenone is converted to mesembrine, mesembrenol and mesembranol.     

Synthesis of new melatoninergic hexahydroindenopyridines

Hexahydroindenopyridine (HHIP) is an interesting heterocyclic framework that contains an indene core similar to ramelteon. This type of tricyclic piperidines aroused our interest as potential melatoninergic ligands. Melatonin receptor ligands have applications in insomnia and depression. We report herein an efficient two-step method to prepare new HHIP by the reaction of an enamine with 3-bromopropylamine hydrobromide. Some synthesized compounds showed moderate affinity for melatonin receptors in the nanomolar or low micromolar range. Furthermore, the methylenedioxy HHIPs 2d (N-phenylacetamide) and 2f (N,N-diethylacetamide), exhibited high selectivity at MT₁ or MT₂ receptors, respectively, when compared with melatonin. It seems that the methylenedioxy group on the indene ring system and the N-acetamide substituent are important structural features to bind selectively MT₁ or MT₂ subtypes.     

Synthesis of betaine lipids: Dipropionylglyceryl(N,N,N-trimethyl)serine

1,2-Dipropionylglyceryl-3-O-3′-(N,N,N-trimethyl)serine was synthesized as a first example of a diglyceride containing an ether-linked hydroxyamino acid with betaine structure. The ether bond was formed by condensation of isopropylideneglycerol (Na alcoholate) and ethyl-2,3-dibromopropionate. Then, the quaternary ammonium group was introduced by replacing the secondary bromine (2-position) with trimethylamine. Finally, the isopropylidene group was split off in acidic medium and the free hydroxyl groups of the glycerol part esterified with propionic acid. The overall yield was 7.5%.     

Cycleanine from Synclisia scabrida: conformational information from the 1H NMR spectrum at 300 MHz

Cycleanine, a bisbenzylisoquinoline alkaloid, has been isolated from the roots of Synclisia scabrida. The ¹H NMR spectrum at 300 MHz reveals that, in chloroform solution, cycleanine has a conformation whereby ring B partly shields ring C′ and ring C is similarly influenced by ring B′.     

Lead optimization of methionine aminopeptidase-2 (MetAP2) inhibitors containing sulfonamides of 5,6-disubstituted anthranilic acids

A series of aryl sulfonamides of 5,6-disubstituted anthranilic acids were identified as potent inhibitors of methionine aminopeptidase-2 (MetAP2). Small alkyl groups and 3-furyl were tolerated at the 5-position of anthranilic acid, while -OCH(3), CH(3), and Cl were found optimal for the 6-position. Placement of 2-aminoethoxy group at the 6-position enabled interaction with the second Mn(2+) but did not result in enhancement in potency. Introduction of a tertiary amino moiety at the ortho-position of the sulfonyl phenyl ring gave reduced protein binding and improved cellular activity, but led to lower oral bioavailability.     

Synthesis and biological evaluation of novel acylhydrazone derivatives as potential antitumor agents

We have designed, synthesized, and evaluated as potential antitumor agents a series of 2-hydroxybenzylidene derivatives of the N-(2-trifluoromethylpiridyn-4-yl)anthranilic acid hydrazide, and some analogues bearing a (2-trifluoromethyl)piridyn-4-ylamino group in 3- or 4-position of benzohydrazide or 4-position of phenylacetohydrazide. Compounds 12e, 13e, 15e, and 16e, bearing a 4-(diethylamino)salicylidene group exhibited potent cytotoxicity, with averaged GI₅₀ values in sub-micromolar range, and a variety of cell selectivity at nanomolar concentrations. The determination of acute toxicity in athymic nudes mice proved some compounds to be non-toxic, making them good candidates for further study as antitumor agents.     

Docking and molecular dynamics studies on triclosan derivatives binding to FabI

FabI, enoyl-ACP reductase (ENR), is the rate-limiting enzyme in the last step for fatty acids biosynthesis in many bacteria. Triclosan (TCL) is a commercial bactericide, and as a FabI inhibitor, it can depress the substrate (trans-2-enoyl-ACP) binding with FabI to hinder the fatty acid synthesis. The structure-activity relationship between TCL derivatives and FabI protein has already been acknowledged, however, their combination at the molecular level has never been investigated. This paper uses the computer-aided approaches, such as molecular docking, molecular dynamics simulation, and binding free energy calculation based on the molecular mechanics/Poisson-Bolzmann surface area (MM/PBSA) method to illustrate the interaction rules of TCL derivatives with FabI and guide the development of new derivatives. The consistent data of the experiment and corresponding activity demonstrates that electron-withdrawing groups on side chain are better than electron-donating groups. 2-Hydroxyl group on A ring, promoting the formation of hydrogen bond, is vital for bactericidal effect; and the substituents at 4-position of A ring, 2′-position and 4′-position of B ring benefit antibacterial activity due to forming a hydrogen bond or stabilizing the conformation of active pocket residues of receptor. While the substituents at 3′-position and 5′-position of B ring destroy the π-π stacking interaction of A ring and NAD⁺ which depresses the antibacterial activity. This study provides a new sight for designing novel TCL derivatives with superior antibacterial activity.     

Identification by gc-ms of 4-chloroindolylacetic acid and its methyl ester in immature Vicia faba seeds

4-Chloroindolylacetic acid and its methyl ester have been converted to the N′-heptafluorobutyryl methyl ester derivative. An extract of immature seeds of Vicia faba has been similarly derivatized. It gave in its mass spectrum the same fragmentation pattern as the synthetic heptafluorobutyryl derivative. The chlorine atom was assigned to the 4-position on the indole ring after comparison by GLC of the extract and of four monochlorinated IAA isomers.     

Isothiocyanatotriphenyl(pyridinium-2-carboxylato)tin(IV) monohydrate

The crystal structure of isothiocyanatotriphenyl- (pyridinium-2-carboxylato)tin(IV) monohydrate is reported. The crystals are monoclinic, space group P2₁/n, a = 10.349(2), b =12.003(2), c = 19.325(4) Å, β = 97.68(2)°, Z = 4, refined to R_F = 0.024 on 4249 observed reflections.The tin(IV) atom is five-coordinate, being bound to three phenyl groups, the isothiocyanato nitrogen atom and an oxygen from the picolinic acid. The geometry around the tin atom is trigonal bipyramidal, with the three phenyl groups occupying the equatorial positions, while the picolinic acid oxygen and the isothiocyanato nitrogen are coordinated axially. The acidic proton of picolinic acid has shifted position in the complex, and is bound to the heterocyclic nitrogen atom. The acid is thus coordinated in the form of a zwitterion. These trigonal bipyramidal units are linked together as dimers by pairs of water molecules, each of which hydrogen- bonds to the non-coordinated carboxylate oxygen atoms of both picolinic acid molecules, plus the heterocyclic nitrogen atom of one picolinic acid molecule. For complex formation with the protonated acid, theheterocyclic nitrogen should be alpha to the carboxylic acid group.     

Study of complex formation with 2-hydroxyiminocarboxylates: specific metal binding ability of 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid

Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H₃L¹) with Cu²⁺ and Ni²⁺ were investigated in solution by potentiometrical and spectral (UV-Vis, EPR, NMR) methods. All Cu²⁺ and most of Ni²⁺ complex species detected in solution were found to have square-planar MN₄ core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N,O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu²⁺ but stronger ones with Ni²⁺ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu²⁺ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni²⁺ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co³⁺ complex K₃[Co(HL¹)₃]·5.5H₂O (1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co³⁺ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings.     

6-Hydrophobic aromatic substituent pyrimethamine analogues as potential antimalarials for pyrimethamine-resistant Plasmodium falciparum

The series of des-Cl (unsubstituted) and m-Cl phenyl analogues of PYR with various flexible 6-substituents were synthesized and studied for the binding affinities with highly resistant quadruple mutant (QM) DHFR. The derivatives carrying 4 atoms linker with a terminal carboxyl substituted on the aromatic ring exhibited good inhibition to the QM enzyme and also showed effective antimalarial activities against resistant P. falciparum bearing the mutant enzymes with relatively low cytotoxicity to mammalian cells. The X-ray crystallographic analysis of the enzyme-inhibitor complexes suggested that the hydrophobic substituent at 6-position was accommodated well in the hydrophobic pocket and the optimal length of the flexible linker could effectively promote the binding of the terminal carboxyl group to the key amino acid residues, Arg59 and Arg122.