The constitution of vertinolide,a new derivative of tetronic acid,produced by Verticillium intertextum

From the culture of Verticillium intertextrum a new tetronic acid derivative, vertinolide, has been isolated as the main constituent of the chloroform extract. Structure 1a was established for vertinolide by X-ray diffraction analysis. Vertinolide (1a) was also transformed to an O-methyl-(1b), an O-acetyl-(1c), a tetrahydro- (1d) and a tetrahydro-O-methyl-derivative (4). The spectroscopic properties of 1a, of its derivatives 1a, 1c, 1d and 4 as well as of three model compounds are compared and discussed.     

Isolation and structure elucidation of three metabolites from verticillium intertextum: sorbicillin, dihydrosorbicillin and bisvertinoquinol

From the culture medium of Verticillium inlertexlum three metabolitcs have been isolated, namely the hexaketidcs sorbicillin (1) and 2'3'-dihydrosorbicillin (2), and the dimeric hexaketide bisvertinoquinol (3). 1 has previously been isolated from Penicillium chrysogenum and also synthesised. Hydrogenation of 1 yielded tetrahydrosorbicillin (8), 2'5'-dihydrosorbicillin (9) and 2',3'-dihydrosorbicillin (2). 2 was also obtained by a BF₃-catalysed condensation of 2,4-dimethyl-resorcinol (5) with (4R^*, 5S^*)-4,5-dibromo-hexanoic acid (6), followed by debromination with zinc and acetic acid. The structure of the dimeric hexaketide 3 (without absolute configuration) was obtained by X-ray structure analysis. It may be considered to be a Diels-Alder adduct of the quinols 11 and 12, the latter being related to 1 and 2, respectively, by simple hydroxylation at C(5). The ¹H and ¹³C NMR signals of 3 and its mono-methyl ether 10 are interpreted and compared with the corresponding properties of 1, 2, vertinolide (4), 3-methoxy-2-methyl-2-cyclohexenone (14), and 2-[(E,E)-2,4-hexadienoyl)]-cyclohexanone (13). The latter was prepared by acylation of the lithium enolate of cyclohexanone with sorbyl chloride. From the spectra of the hexaketides from V. intertextum several patterns have been extracted which are characteristic for some common and some distinguishing substructures in these natural products.     

Hydride Abstraction from Benzocyclopropene. Preliminary communication

The reaction between benzocyclopropene ( 1 ) and triphenylmethyl fluoroborate in acetonitrile shows an isotope effect of 6.7 and the isolation of the resulting triphenylmethane and benzaldehyde has been effected. A mechanism for the formation of the latter is proposed, involving an intermediate benzocyclopropenium ion ( 2 ).     

Isolation and structure analysis of a photoproduct of the new photoaffinity label p-nitrophenylalanine. Preliminary communication

The isolation and structural analysis of a photoproduct of Ac · p-nitrophenyl-alanine ethyl ester is described and discussed. Nitrophenylalanine is proposed as a hydrogen fluoride stable photoaffinity label.     

Twista-4,9-diene. Preliminary communication

A synthesis of twista-4,9-diene ( 17 ) from tricyclo[4.3.1.0^3,8]dec-4-en-10-one ( 2 ) is described.     

Light-induced dehydrodimerization of pyrroles. Preliminary communication

Irradiation (λ>280 nm) of 3-hydroxypyrroles 1 in acetonitrile leads to the formation of 3,3′-bi-3H-pyrroles 2 in reasonable to good yields.     

A Photo-initiated Wagner-Meerwein Rearrangement. Preliminary communication

Irradiation of the octalin-derived sesquiterpene oxide α-agarofuran in methanol leads to rearrangement to the perhydroazulene system, in addition to simple double-bond migration to β-agarofuran. This rearrangement apparently proceeds through a carbonium-ion-like intermediate, whereas conventional generation of a carbocation leads only to opening of the oxide ring without rearrangement.     

The Electrocyclic Cyclopropyl-Allyl Rearrangement. Preliminary communication

MINDO-2 SCF calculations indicate that ring-opening of cyclopropyl radical (I) to allyl radical (II) is more favourable via a disrotatory reaction path, the calculated activation energy being ～30 kcal/mole. (For conrotatory opening the activation energy was found to be ～44 kcal/mole.) The two critical motions of the nuclei during the transformation are found to be strongly decoupled, i.e. rupture of the CH₂βCH₂ bond precedes rotation of the CH₂ groups. As predicted by qualitative theories both ring-opening modes are unfavourable since they involve a change in electronic ground-state symmetry between I and II. The preferred ring-opening mode is discussed qualitatively in terms of Evans' principle.     

Dendrophanes: Water-Soluble Dendritic Receptors. Preliminary communication

The dendritic cyclophanes (dendrophanes ) 1–3 containing a [6.1.6.1]paracyclophane as the initiator core embedded in dendritic poly(ether-amide) shells of first ( 1 ), second ( 2 ), and third ( 3 ) generation were prepared and characterized. The X-ray crystal-structure analyses of esters 7 and 4 , derivatives of cyclophane core 9 and first-generation dendrophane 1 , respectively, displayed open cavity binding sites suitable for the inclusion complexation of aromatic substrates. With their carboxylate surface groups, dendrophanes 1–3 were readily soluble in aqueous phosphate buffer (pH 8.0), and the complexation of naphthalene derivatives was investigated by ¹H-NMR and fluorescence titrations. The binding studies demonstrated that the cyclophane cavity remains open and accessible to appropriate substrates even at higher dendritic generations. The 1:1 complexes formed in aqueous buffer were of similar stability to those formed by the unbranched core 9 (K_a between 1000 and 10000 1 mol^?1, 300 K). Investigations with the fluorescent probe 6-(p-toluidino)naphthalene-2-sulfonate ( 12 ) showed that the micropolarity at the dendrophane core decreases with increasing generation number.     

Thermal Interconversion of Phenylcarbene and Tropylidene. Preliminary communication

Phenylcarbene and tropylidene interconvert in the gas-phase, as evidenced by the formation of stilbene and heptafulvalene ( 5 ) from both at 300°. Heptafulvalene itself rearranges to stilbene and anthracene above 500°. Phenylcarbene, but not tropylidene, undergoes ring contraction to fulvenallene ( 9 ) at 900°. Formation of fluorene from diphenylcarbene involves a complete ring expansion to 2-phenyltropylidene ( 14 ), and subsequent ring contraction to 2-biphenylylcarbene ( 15 ).     

The Adamantane Rearrangement of 1,2endo-Trimethylenenorbornane. Preliminary communication

1,2endo-Trimethylenenorbornane (1) in the presence of aluminium bromide in carbon disulfide at ?60° isomerizes at a much higher rate than its 2exo-isomer 2 to 2endo, 6endo-trimethylenenorbornane (3) as the sole product. By consequence, the hydrocarbon 2 being the next intermediate in the sequence of the adamantane rearrangement of 1 seems to be very unlikely.     

On the stereochemistry of allylmetal-aldehyde condensations. Preliminary communication

The stereochemical course of the intramolecular allylsilane-aldehyde condensation of 1a has been investigated. A modest preference for the product arising from a synclinal orientation of double bonds was observed with Lewis-acid catalysts. Cyclization induced by fluoride ion resulted in stereochemical reversal.     

Reactions of Diazo Compounds with Imines. Preliminary communication

The [Rh₂(OAc)₄]-catalyzed addition of methyl diazoacetate to N-benzylideneaniline ( 1a ) afforded the imine cis- 2 in 35% yield. Under catalysis by chiral Rh^II catalysts, however, only racemic 1a was produced, and the yield was low. In the presence of dimethyl maleate, aziridine formation was suppressed, and an intermediate ylide 6 was trapped as cycloadduct 7 . No aziridines were obtained, however, from 1b, 1c , and 3 . The iminium salt 8 reacted with (trimethylsilyl)diazomethane in the absence of [Rh₂(OAc)₄] via dipolar cycloaddition followed by extrusion of N₂ to 10 .     

Breakdown of Chlorophyll: A Tetrapyrrolic Chlorophyll Catabolite from Senescent Rape Leaves. Preliminary communication

The experiments leading to the isolation and to the elucidation of the constitution of Bn-NCC-1, a colourless non-fluorescent chlorophyll catabolite from senescent cotyledons of rape (Brassica napus L.), are described. A series of fast-atom-bombardment (FAB) mass and ¹H- and ¹³C-NMR spectral experiments are used to determine the constitution of the catabolite Bn-NCC-1. The structural information available indicates Bn-NCC-1 to be a 1-formyl-19-oxobilane, structurally related to ‘RP 14’, isolated earlier from artificially aged primary leaves of barley. The major differences between the constitution of the metal-free chlorophyll pheophorbide a and that of Bn-NCC-1 concern oxygenolytic opening of the porphinoid macrocycle at C(4)? C(5), saturation at the other meso positions, hydrolysis of the methyl-ester function, and functionalization by a malonic-acid unit of the side chain at C(8). This work provides for the first time the structural data of a chlorophyll-degradation product from senescent plant leaves formed under normal growth conditions.     

1,1-Dihalogenoanthra [b]cyclopropenes. Preliminary communication

1,1-Dichloro- and 1,1-difluoroanthra [b]cyclopropene ( 1 and 2 ) are synthesized in 8 steps from the Diels-Alder adduct of benzocyclobutene and maleic anhydride.     

Structural Modifications of Chaparrinone Using Benzeneseleninic Anhydride. Preliminary communication

Treatment of chaparrinone triacetate with benzeneseleninic anhydride afforded in addition to the Δ^14,15-dehydro compound two products arising from angular hydroxylation at C(5). The mechanism of this reaction is discussed. The corresponding deacetylated compounds do not display significant antineoplastic activity.     

穿心莲内酯硫酸酯化反应体系中四个新的衍生物的分离与表征

通过色谱方法, 从复杂的穿心莲内酯硫酸酯化反应体系中分离获得4个新的穿心莲内酯衍生物, 应用谱学方法进行了表征. 主要利用1H NMR, 13C NMR, DEPT, 1H-1H COSY, HSQC, HMBC及NOSEY等1D和2D NMR技术, 并通过与母体化合物NMR数据的对比分析, 鉴定这4个化合物分别为3,19-二羟基-8,11,13-赖百当三烯-15,16-内酯(1), 3-羟基-8,11,13-赖百当三烯-15,16-内酯-19-硫酸酯(2), 8,11,13-赖百当三烯-15,16-内酯-3,19-二硫酸酯(3), 3-羟基- 8(R)-12(S)-8(12)-环氧-13-赖百当烯-15,16-内酯-19-硫酸酯(4).