Beta-triketone inhibitors of plant p-hydroxyphenylpyruvate dioxygenase: modeling and comparative molecular field analysis of their interactions

p-Hydroxyphenylpyruvate dioxygenase (HPPD) is the target site of beta-triketone herbicides in current use. Nineteen beta-triketones and analogues, including the naturally occurring leptospermone and grandiflorone, were synthesized and tested as inhibitors of purified Arabidopsis thaliana HPPD. The most active compound was a beta-triketone with a C(9) alkyl side chain, not reported as natural, which inhibited HPPD with an I(50) of 19 +/- 1 nM. This is significantly more active than sulcotrione, which had an I(50) of 250 +/- 21 nM in this assay system. The most active naturally occurring beta-triketone was grandiflorone, which had an I(50) of 750 +/- 70 nM. This compound is of potential interest as a natural herbicide because it can be extracted with good yield and purity from some Leptospermum shrubs. Analogues without the 1,3-diketone group needed to interact with Fe(2+) at the HPPD active site were inactive (I(50)s > 50 microM), as were analogues with prenyl or ethyl groups on the triketone ring. Modeling of the binding of the triketones to HPPD, three-dimensional QSAR analysis using CoMFA (comparative molecular field analysis), and evaluation of the hydrophobic contribution with HINT (hydropathic interactions) provided a structural basis to describe the ligand/receptor interactions.

Bullatenone, 1,3-dione and sesquiterpene chemotypes of Lophomyrtus species

The only known natural source of the volatile bioactive compounds bullatenone 1 and 4-methyl-1-phenylpentane-1,3-dione 2 is the New Zealand endemic shrub Lophomyrtus bullata (Myrtaceae). GC and NMR analyses of essential oils and solvent extracts of L. bullata, L. obcordata and the hybrid L. "ralphii" showed several chemotypes, which did not correlate with species. Levels of 1 and 2 varied from dominant to low/undetectable and the most common chemotype was rich in allo-aromadendrene and other sesquiterpenes. The rare natural product E-4-methyl-1-phenyl-1-penten-3-one 4 was detected for the first time in this genus. The non-volatile cytotoxic compound bullataketal 5 co-occurred with bullatenone 1. An essential oil from the relatively rare bullatenone 1 chemotype showed antifungal activity against Candida albicans and Cladosporium resinae, and an oil from the 4-methyl-1-phenylpentane-1,3-dione 2 chemotype showed antibacterial activity against Bacillus subtilis.

Triketones active against antibiotic-resistant bacteria: Synthesis, structure–activity relationships, and mode of action

A series of acylated phloroglucinols and triketones was synthesized and tested for activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VRE) and multi-drug-resistant Mycobacterium tuberculosis (MDR-TB). A tetra-methylated triketone with a C12 side chain was the most active compound (MIC of around 1.0 microg/ml against MRSA) and was shown to stimulate oxygen consumption by resting cell suspensions, suggesting that the primary target was the cytoplasmic membrane.

Novel chemotaxonomic markers of the Alternaria infectoria species-group

Two new structurally related metabolites, novae-zelandin A (1) and novae-zelandin B (2), as well as the novel metabolite 4Z-infectopyrone (3) were purified from extracts of filamentous fungi belonging to the Alternaria infectoria species-group. The structures were elucidated by a combination of 1D and 2D NMR spectroscopic data and MS data. 1-3 are important chemotaxonomic markers of the A. infectoria species-group and exhibit structures similar to those of known biologically active compounds, suggesting that they could be potential phytotoxins.

Sesquiterpenes from the New Zealand Liverwort Lepidolaena hodgsoniae

NMR studies have shown that seven new sesquiterpenoids, 3, 4, 5a, and 7-10, isolated from dried samples of the New Zealand liverwort Lepidolaena hodgsoniae have the same substituted cyclopentapyran ring system as the previously described insecticidal sesquiterpene diene hodgsonox (1), which has been reported only from this plant. In all but one compound, 10, the 1,1-disubstituted double bond of hodgsonox has migrated into an endocyclic position, but only two, 5a and 9, have the double bonds in conjugation. These seven new compounds represent a variety of different oxidation levels. Two of the new derivatives, 9 and 10, were isolated only from an aged sample and are presumably artifacts. The only other terpenoid isolated in significant quantity was (7R,10R)-calamenene (2).

Synthesis of the 3-methylene-2-vinyltetrahydropyran unit; the hallmark of the sesquiterpene, hodgsonox

[structure: see text] The synthesis of some simple compounds containing the previously unreported 3-methylene-2-vinyltetrahydropyran system, a unique feature of the liverwort metabolite, hodgsonox is reported. Key features are the creation of an acrolein substituted in the alpha-position with a three-carbon chain bearing a terminal electrophilic site, addition of a vinyl group, and cyclization.

Essential oils from New Zealand manuka: triketone and other chemotypes of Leptospermum scoparium

The triketone chemotype of manuka, Leptospermum scoparium (Myrtaceae), is commercially important because of its antimicrobial activity. Oils from 36 individual plants on the East Cape of New Zealand all showed similar high triketone contents (>20% total triketones) with little seasonal variation. Analyses of oils from 261 individual manuka plants collected from 87 sites throughout New Zealand showed that the high triketone chemotype was localised on the East Cape, although oils with triketone levels up to 20% were found in the Marlborough Sounds area of the South Island. Cluster analysis revealed other chemotypes localised on other areas. Ten further chemotypes are described: alpha-pinene; sesquiterpene-rich with high myrcene; sesquiterpene-rich with elevated caryophyllene and humulene; sesquiterpene-rich with an unidentified sesquiterpene hydrocarbon; high geranyl acetate; sesquiterpene-rich with high gamma-ylangene + alpha-copaene and elevated triketones; sesquiterpene-rich with no distinctive components; sesquiterpene-rich with high trans-methyl cinnamate; high linalol; and sesquiterpene-rich with elevated elemene and selinene. Some of the chemotypes contained aroma compounds at relatively high levels, with a geranyl acetate-rich oil being most notable. Possible origins for this complex array of chemotypes are proposed.

Ether-linked biflavonoids from Quintinia acutifolia

The New Zealand tree Quintinia acutifolia has yielded four biflavonoids, the new 2,3,2'',3''-tetrahydroochnaflavone (3), and its 7,7''-di-O-methyl derivative (1). The rare 7-O-methyl-2,3,2'',3''-tetrahydroochnaflavone (2) and 2'',3''-dihydroochnaflavone (4), both previously identified only from members of the Ochnaceae, were also isolated. Structures were determined by spectroscopic methods. This is the first report of biflavonoids from the Grossulariaceae.

Determination of the absolute configuration ofAnisotomeirregular diterpenes: Application of CD and NMR methods

Several Anisotome diterpene derivatives were synthesized in an attempt to obtain a crystalline compound for X-ray analysis. Although we were unable to obtain a suitable crystal, the absolute configuration of the irregular diterpene skeleton was determined using two other techniques: a circular dichroism (CD) protocol based on a tetraarylporphyrin molecular tweezer that allowed prediction of the absolute stereochemistry on a microscale level, and a method employing differences in NMR shifts from derivatization of the naturally occurring acid 1 with enantiomers of a phenylglycine methyl ester (PGME) chiral anisotropic reagent. The excellent agreement between the CD and NMR methods led to the assignment of a 2S-absolute configuration for anisotomenoic acid 1.

2-Hydroxyflavanones from Leptospermum polygalifolium subsp. polygalifolium Equilibrating sets of hemiacetal isomers

2,5-Dihydroxy-6-methyl-7-methoxyflavanone and its isomer 2,5-dihydroxy-8-methyl-7-methoxyflavanone have been identified as the principal components in the ethanol extract of L. polygalifolium subsp. polygalifolium. The former compound has been separated from the latter for the first time by crystallisation. Other flavonoids identified include an equilibrating mixture of novel 2,3,5-trihydroxyflavanones; the first discovery of this type of compound from a natural source. This study has also confirmed the presence of the triketones, flavesone and leptospermone, along with the closely related isoleptospermone as anti-microbial components.

Biosynthesis of the sesquiterpene hodgsonox from the New Zealand liverwort Lepidolaena hodgsoniae

The incorporation of [1-13C] labelled glucose into hodgsonox, a sesquiterpene epoxide with a unique, doubly allylic ether functionality has been studied in axenic cultures of the liverwort Lepidolaena hodgsoniae. Quantitative 13C NMR spectroscopic analysis showed that the isoprene units are derived exclusively from the methylerythritol phosphate pathway.

The first atisane diterpenoids from a liverwort: polyols from Lepidolaena clavigera

Two new diterpenoids were isolated from the New Zealand liverwort Lepidolaena clavigera. Spectroscopic studies identified the structures as atisanes 1 and 2, with an unprecedented level of oxygenation. This is the first report of the atisane skeleton from a liverwort. Compound 2 showed cytotoxic and insecticidal activity. [structure: see text]

Laurenanes: fenestranes with a twist

Four isomeric alcohols derived from the diterpene lauren-1-ene (1) have been examined by NMR methods (nuclear Overhauser enhancements, coupling constants, and variable-temperature studies) and by molecular mechanics using the MM3 force field to investigate a conformational twisting of the [5.5.5.7]fenestrane ring system. Results have been correlated with a concurrent study of remote functionalization reactions induced by iodobenzene diacetate/iodine under ultrasonic irradiation. Three of the laurenan-2-ols, 6, 7, and 8, lead to the same tetrahydrofuran derivative, 2beta,14beta-epoxylaurenane (9), and evidence for beta-cleavage of the alkoxy radical intermediate is obtained through the isolation of a ring-cleavage product 11 with a rearranged carbon skeleton. The products from the remaining alcohol 3 demonstrate solution dynamics involving the conformational twisting of the laurenane skeleton.

Hodgsonox, a new class of sesquiterpene from the liverwort Lepidolaena hodgsoniae. Isolation directed by insecticidal activity

Hodgsonox (1), a new insecticidal sesquiterpene, has been isolated from the New Zealand liverwort Lepidolaena hodgsoniae. The structure was elucidated on the basis of 2D NMR analysis of 1 and a synthetic epoxide derivative (2). Hodgsonox represents a new class of sesquiterpene with a cyclopenta[5,1-c]pyran ring system fused to an oxirane ring. The combination of a mono- and a 1,1 disubstituted double bond flanking the oxygenated carbon of a the pyran ring is a unique structural feature. Hodgsonox is toxic to larvae of the blowfly Lucilia cuprina.

Chemistry of New Zealand Apiaceae: New irregular diterpenes from Anisotome flexuosa and A. haastii showing conformational exchange

Two new derivatives of a recently-reported class of irregular diterpene have been discovered in New Zealand species of the Apiaceae family. 16-Acetoxyanisotomenoic acid (8) (3,3a,4,4-tetramethyl-3-{(Z)-5-acetoxy-4-methyl-3-pentenyl}-2,3,3a,4,5,6-hexahydro-1H-2-indenecarboxylic acid) and anisotomene-1,12-diol (11) (3,3a,4,4-tetramethyl-3-(2-hydroxy-4-methyl-3-pentenyl)-2,3,3a,4,5,6-hexahydro-1H-2-indenyl) methanol) have been obtained from the sub-alpine plants, Anisotome flexuosa and A. haastii respectively. 13 C nuclear magnetic esonance (n.m.r.) spectra of the anisotomene derivatives are complicated by line broadening. Molecular modelling of anisotomenoic acid (1) and anisotomenol (2) suggests that this is due to conformational exchange in the highly substituted bicyclo [4,3,0] non-1-ene ring system.

beta-triketones from myrtaceae: isoleptospermone from leptospermum scoparium and papuanone from corymbia dallachiana

Naturally occurring beta-triketones, isoleptospermone [3, 5-hydroxy-4-(2-methyl-1-oxopentyl)-2,2,6, 6-tetramethyl-4-cyclohexene-1,3-dione) from Leptospermum scoparium] and papuanone [6, 5-hydroxy-4-(1-oxohexyl)-2,2,6, 6-tetramethyl-4-cyclohexene-1,3-dione from Corymbia dallachiana], have been synthesized. Full spectral data are reported for the first time. The 13C NMR spectra of 3, 6, and the other triketones flavesone (2), leptospermone (4), and grandiflorone (5) found in Myrtaceous plants are fully assigned.

11-oxygenated cytotoxic 8,9-secokauranes from a New Zealand liverwort, Lepidolaena taylorii

Four new cytotoxic 8,9-secokauranes have been identified from the liverwort Lepidolaena taylorii. The 11-oxygenation found in three of these has not been encountered in the 8,9-secokauranes known from higher plants. NMR studies were combined with molecular modelling to determine the preferred conformations. Six structurally related kauren-15-ones were also found, including three new compounds. Some of these compounds showed differential cytotoxic activity against human tumor cell lines. The probable mode of cytotoxic action was supported by Michael addition of a thiol. Two 8,9-secokauranes were the main cytotoxins in another New Zealand liverwort. L. palpebrifolia.

Reaction of Imidazoles with Cyanogen Bromide: Cyanation at N 1 or Bromination at C 2?

The reaction in acetonitrile solution of a number of imidazoles(1H-, 1-methyl-, 2-methyl-, 4-methyl-, 1,2-, 1,4- and1,5-dimethyl-, 1-ethyl-, 1-benzyl- and 1-butyl-imidazole) and imidazolecomplexes([Co(NH3)5(imH)](ClO4)3,[Co(NH3)5(im)](ClO4)2 and[Co(NH3)5(1-Meim)](ClO4)3) with BrCN has beenstudied. Those imidazoles bearing an N-alkyl substituent and having a hydrogenat C2 react to give the 2-bromo products, while the N-H imidazoles react togive N-cyano derivatives. The product(s) from thereaction of 1,2-dimethylimidazole with BrCN could not be characterized. Of thecomplexes, only[Co(NH3)5(im)](ClO4)2 reacts, giving the 2-bromoproduct. Our observations suggest a lone pair on a ring nitrogen atom isnecessary for an imidazole to react with BrCN, and a possible mechanism issuggested. The X-ray structure of 2-methylimidazole-1-carbonitrile isreported. Crystal data (–143°C) forC5H5N3:monoclinic, P21/c, a10·201(5), b 7·110(3),c 7·227(3) Å, β 100·47(2)°,V 515·4(4) Å 3 , Z 4,dcalcd 1·380 gcm¯3 . Refinement of the structure converged withR1 0·0444 for 1183reflections with Fo >4F(Fo) andwR2 0·1259 for all 1278data.

Synthesis of geranyl phenyl ethers based on the cytotoxic monoterpenoids from the liverwort genus trichocolea

The synthesis of three geranyl ethers, methyl 4-[(2E)-3, 7-dimethyl-5-oxo-2,6-octadienyloxy]-3-methoxybenzoate (1), methyl 4-[(2E)-3,7-dimethyl-2,6-octadienyloxy]-3-methoxybenzoate (2), and methyl 4-[(2E)-3,7-dimethyl-2,6-octadienyloxy]-3-hydroxybenzoate (3), previously isolated from New Zealand Trichocolea liverworts, is described. Differing reactivity of the hydroxy groups of methyl protocatachuate toward alkylation and the ability of alkyl groups to migrate from oxygen to an ortho-oxygen in these benzene derivatives are noted.

A New Tetracycle from Dimerization of the N-Methylpyridazinium Ion in Aqueous Solution

In a one-pot synthesis at room temperature the N-methylpyridazinium ion (1) dimerizes stereospecifically and with 100 % conversion in a series of OH^- -catalyzed processes to give a new tetraazafluorene (2). Four of the individual steps can be identified directly and monitored by ¹ H NMR spectroscopy.

Geranyl Phenyl Ethers from the New Zealand Liverwort Trichocolea hatcheri

Methyl 4-(geranyloxy)-3-hydroxybenzoate (6), previously unreported, has been identified from the New Zealand liverwort Trichocolea hatcheri. Four new related 3-hydroxybenzoates 7-10 were also found, with a carbonyl at C-5 of the geranyl group and various double bond arrangements. Two known geranyl phenyl ethers 1 and 3, found in other Trichocolea species, were also identified.

The Chemistry of Lauren-1-ene. XVII Preparation of Unsaturated Oxa and Aza Tetracycles

Several lauren-1-ene-derived compounds containing an exocyclic methylene grouping have been synthesized. These include substances with both regular and rearranged carbon frameworks. The X-ray structure of a rearranged α-methylene lactone shows that an earlier assignment of stereochemistry is incorrect and that this compound has an exceptionally distorted C=C-C=O unit. The methylene derivatives prepared have proved to have low cytoxicity.

Isoprenyl phenyl ethers from liverworts of the genus Trichocolea: cytotoxic activity, structural corrections, and synthesis

The main cytotoxic component in New Zealand collections of the liverwort Trichocolea mollissima was identified as methyl 4-[(5-oxogeranyl)oxy]-3-methoxybenzoate, a structure that has not been reported previously. Two double-bond isomers of this geranyl ether were present at lower levels. Reinvestigation of the benzoates from Japanese collections of Trichocolea tomentella led to the identification of four geranyl ethers (including two of the three compounds identified from T. mollissima), which had previously been assigned incorrect geranyl ester structures. One compound, previously reported as a 3,3-dimethylallyl ester, could not be reisolated from T. tomentella, but was found in a New Zealand collection of Trichocolea lanata. It was shown to be a 3,3-dimethylallyl ether by synthesis from methyl vanillate. Several of these compounds were active in cytotoxic and antifungal assays.

The glycosidic precursor of (Z)-5-ethylidene-2(5H)-furanone in Halocarpus biformis juvenile foliage

A new glycosidic lactone, (5R,6R)-5-(1-hydroxyethyl)-2(5H)-furanone beta-D-glucopyranoside, has been identified as the principal precursor of (Z)-5-ethylidene-2(5H)-furanone in juvenile foliage of the New Zealand tree Halocarpus biformis. Three related lactone glycosides were isolated in smaller amounts, together with the known phenolic glycosides pyroside, arbutin and picein. The principal lactone glycoside underwent facile elimination of glucose, in neutral or basic conditions, to yield (Z)-5-ethylidene-2(5H)-furanone and its E-isomer. This lactone glycoside was also detected in foliage of H. bidwillii and H. kirkii.

The Chemistry of Laurenene. XVI. Investigation of the Mechanism of a Cationic Rearrangement

Some aspects of the mechanism of the acid-induced rearrangement of laurenan-2β-ol have been deduced from deuterium- labelling studies. A key intermediate arises from two pathways, one involving a 1,4- and one a 1,5-hydride shift. Formation of this intermediate is partially suppressed by substitution of the migrating hydrogen by a deuterium. A proposed pathway which involves a 1,3-methyl migration has been disproved, and scrambling and loss of deuterium label has been accounted for in terms of equilibria involving lauren-1-ene and another previously reported rearrangement product. The rearrangement is strongly promoted in dichloromethane, and the product composition is highly solvent-dependent.

Diiodo Acetals and Unsaturated Lactones From Dihydropyran

Reaction of dihydropyran with propiolic acid and N- iodosuccinimide gave an iodo ester which was cyclized under free-radical conditions to form an (E) iodomethylene lactone. Photolysis of this lactone could be controlled to generate mixtures of (E) and (Z) iodomethylene lactones, or alternatively the iodine-free methylene lactone. The structures of some by-products of the iodo ester formation have been shown to be a succinimide derivative and two stereoisomers of a diiodo acetal. X-Ray determination of the structure of one of the diiodo acetal isomers is described.

The Chemistry of Laurenene. XV. Preparation of 15βH-Lauren-1-ene and Deuterium-Labeled Laurenan-2β-ol

A synthesis of laurenan-2β-ol labelled with deuterium at various positions has been undertaken to infer various points about a rearrangement mechanism. During this work, syntheses of the 15-epimer of lauren-1-ene and some derivatives were also developed.

The Chemistry of Laurenene. XIV. New Rearrangements of a Ring A Seco Ester

Adsorption on neutral alumina of a keto ester derived from the diterpene lauren-1-ene has been shown to yield a new keto ester with an unusual bridged tricyclic ring system. With trifluoroacetic acid, both keto esters yield a further new compound which contains a benzene ring. The transformations involved may be rationalized in terms of carbocationic rearrangements. An alcohol derived from the compound with the bridged tricyclic ring system has been converted into a cyclopentacyclononene derivative by β -cleavage of the alkoxy radical.