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.