Antimicrobial activity of amino acid,imidazole, and sulfonamide derivatives of pyrazolo[3,4-d]pyrimidine

Derivatives of pyrazolo[3,4-d]pyrimidine with amino acid 3a–d , imidazole 4a–d , carbonyl 6–9 , pyrazole 10 , pyrazolone 11 , and sulfonamide 12–17 moieties were synthesized. Structure of the new compounds were established by their elemental analyses and spectral data. Some of the synthesized compounds were tested in vitro for their antimicrobial activity. Compounds 4b, 12 , and 16 were almost as potent as the standard antibiotic Chloramphenicol as positive control. Also, compounds 3b, 3c, 12 , and 16 were nearly as active as Terbinafine as positive control. © 2003 Wiley Periodicals, Inc. 15:57–62, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10212     

Ferroelectric and piezoelectric properties of a quenched poly(vinylidene fluoride-trifluoroethylene) copolymer

The ferroelectric and piezoelectric properties of melt-quenched unoriented poly(vinylidene fluoride-trifluoroethylene) (73 : 27) copolymer films as a function of the number of poling cycles have been studied. The investigation revealed that quenched films exhibit a decrease in D-E hysteresis behavior as the number of poling cycles increases when the samples are poled at room temperature. Corresponding decreases in remanent polarization, Pr, as well as small increases in the coercive field, Ec, were observed as the material was subjected to successive poling cycles. The piezoelectric coefficients, d₃₁ and e₃₁, also decreased as the number of poling cycles increased. In addition, a clear reduction in the “apparent” Curie transition temperature between unpoled and poled material was observed. Preliminary evidence indicates that films quenched from the melt to below T_c do not form a stable ferroelectric crystal phase as previously believed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2671–2679, 1997     

Identification and differentiation of dragon's blood in works of art using gas chromatography/mass spectrometry

Dragon's blood is a common but non-specific name for red-coloured resins that are produced by various plants, particularly exudations from plant species belonging to the genera Dracaena and Daemonorops. Although dragon's blood is mentioned in historic sources as a colourant, it has hardly ever been identified in real artworks. This paper reports the identification and discrimination of dragon's blood produced by Dracaena cinnabari, Dracaena draco as well as Daemonorops draco and Daemonorops micracantha by means of gas chromatography/mass spectrometry (GC/MS) within the context of a routine analysis of binding media used in works of art. The detection of specific flavonoid marker compounds in both underivatised and methylated methanol extracts provided the first evidence for the use of dragon's blood from all four species in various works of art from the fifteenth to nineteenth centuries. Dragon's blood was mainly used as a red colourant in gold lacquers as well as translucent glazes and paints, e.g. in reverse-glass paintings (Hinterglasmalerei).     

Dimeric Manganese-Catalyzed Hydroalkenylation of Alkynes with a Versatile Silicon-Based Directing Group

Herein, we present a manganese-catalyzed, branched-selective hydroalkenylation of terminal alkynes, under mild conditions through facile installation of a versatile silanol as a removable directing group. With an alkenyl boronic acid as the coupling partner, this reaction produces stereodefined (E,E)-1,3-dienes with high regio-, chemo- and stereoselectivity. The protocol features mild reaction conditions such as room temperature and an air atmosphere, while maintaining excellent functional group compatibility. The resulting 1,3-dienesilanol products serve as versatile building blocks, as the removal of the silanol group allows for the synthesis of both branched terminal 1,3-dienes for downstream coupling reactions, as well as stereoselective construction of linear (E,E)-1,3-dienes and (E,E,E)- or (E,E,Z)-1,3,5-trienes. In addition, a Diels–Alder cycloaddition can smoothly and selectively deliver silicon-containing pentasubstituted cyclohexene derivatives. Mechanistic investigations, in conjunction with DFT calculations, suggest a bimetallic synergistic activation model to account for the observed enhanced catalytic efficiency and good regioselectivity.     

New Carbonyl Compounds in the High-Boiling Fraction of Lavender Oil. 3rd Communication

The occurrence of a series of new constituents which can be considered as Diels-Alder adducts of methyl vinyl ketone and ocimene (→1–4), myrcene (→ 9 , 10 ) or β-far-nesene ( → 11 , 12 ), respectively, was reported. Furthermore, the structures of four isomeric cyclohexene derivatives could be established as adducts 21–24 of (E, Z)- and (E, E)-1,3,5-undecatrience and methyl vinyl ketone. Another series of constituents having the norbornane skeleton represents adducts 25–32 , and 33–40 of methyl cyclopentadiene and 1-octen-3-one or methyl vinyl ketone, respectively. In accordance with Alder's endo-rule the endo-isomers are preponderant in the natural as well as in the synthetic mixtures. Most of these constituents could also be identified in a lavender absolute as well as in a freshly prepared hexane extract of lavender flowers (Lavandula officinalis CHAIX ).     

Distribution of polymer deposition in plasma polymerization. III. Effect of discharge power

Distribution of polymer deposition in an inductively coupled rf discharge system is studied as a function of level of discharge power with acetylene and styrene as monomers. When a fixed flow rate is used, the discharge power has a relatively small effect on the pattern of distribution of polymer deposition as long as values of W/FM, where W is discharge wattage, F is flow rate, and M is molecular weight of monomer, are maintained above a critical level to maintain full glow in the reaction tube. It has been shown that plasma polymerization of two monomers which have different molecular weights can be compared in a fair manner by selecting conditions to yield similar value of W/FM.     

The Overall Hyper-Wiener Index

The concept of overall connectivity of a graph G was extended here to the definition of the overall hyper-Wiener index OWW(G) of a graph G, defined as the sum of the hyper-Wiener indexes in all subgraphs of G, as well as the sum of eth-order terms, ^e OWW(G), with e being the number of edges in the subgraph. The potential usefulness of the overall hyper-Wiener index in QSAR/QSPR is evaluated by its correlation with a number of properties of C3-C8 alkanes and cycloalkanes.     

REDUCED NEAR-UV SENSITIVITY IN Phycomyces MUTANTS AFFECTED IN THE BIOSYNTHESIS OF 6,7-DIMETHYL-8-RIBITYLLUMAZINE

Riboflavin-requiring mutants of Phycomyces blakesleeanus with defects in the genes ribA, ribB, ribC and ribD were analyzed with respect to their contents of flavins, 6,7-dimethyl-8-ribityllu-mazine (DMRL) and pterins as well as their phototropic sensitivity. Strains were grown on minimal medium enriched with 10^?6M riboflavin (RB), and the concentrations of the respective pigments in sporangiophores were determined by HPLC. In strains A607 ribC401 and A641 ribC402 madA7 a loss of DMRL correlated with a loss of near-UV sensitivity. In general terms, the results suggest the participation of DMRL in photoreception, which does not necessarily imply DMRL as a photoreceptor chromophore. In more specific terms, the result could be understood on the basis of a UV/blue-light photoreceptor, which includes besides a flavin also a lumazine-like chromophore. Mutants C318 ribA I and C323 ribA4 accumulated DMRL, the immediate precursor of RB, as well as biopterin and neopterin. Mutant C322 ribB contained normal amounts of DMRL and pterins. Mutant C324 ribD5 had reduced amounts of neopterin and biopterin. The fact that some of the RB-requiring mutants displayed abnormal amounts of pterins indicates a common regulation for the flavin and the pterin pathway.     

Dipolare (1:1)-Addukte aus der Reaktion von 3-Amino-2H-azirinen mit 1,3,4-Oxadiazol- und 1,3,4-Thiadiazol-2(3H)-onen

Dipolar 1:1 Adducts from the Reaction of 3-Amino-2H-azirines with 1,3,4-Oxadiazol- and 1,3,4-Thiadiazol-2(3H)-ones 3-Amino-2H-azirines 1 react with 5-(trifluoromethyl)-1,3,4-oxadiazol-2(3H)-one ( 2 ) as well as with different 5-substituted 1,3,4-thiadiazol-2(3H)-ones ( 5a–e ) in 2-propanol at room temperature to give dipolar 1:1 adducts of type 3 and 6 , respectively, in reasonable-to-good yields (Schemes 3 and 6, Tab. 1 and 2). The structure of two of these dipolar adducts, 6a and 6e , which are formally donor-acceptor-stabilized azomethin imines, have been elucidated by X-ray crystallography (Figs. 1-4). In the reaction of 2 and sterically crowded 3-amino-2H-azirines 1c–e with a 2-propyl and 2-propenyl substituent, respectively, at C(2), a 4,5-dihydro-1,2,4-triazin-3(2H)-one of type 4 is formed as minor product (Scheme 3 and Table 1). Independent syntheses of these products proved the structure of 4 . Several reaction mechanisms for the formation of compounds 3 and 4 are discussed, the most likely ones are described in Scheme 4: reaction of 2 as an NH-acidic compound leads, via a bicyclic zwitterion of type A , to 3 as well as to 4 . In the latter reaction, a ring-expanded intermediate B is most probable.     

What to Learn from a Comparative Genomic Sequence Analysis of <Emphasis Type="Italic">L</Emphasis>-Carnitine Dehydrogenase

Summary. In contrast to eukaryotic cells certain eubacterial strains have acquired the ability to utilize L-carnitine (R-(–)-3-hydroxy-4-(trimethylamino)butyrate) as sole source of energy, carbon and nitrogen. The first step of the L-carnitine degradation to glycine betaine is catalysed by L-carnitine dehydrogenase (L-CDH, EC 1.1.1.108) and results in the formation of the dehydrocarnitine. During the oxidation of L-carnitine a simultaneous conversion of the cofactor NAD⁺ to NADH takes place. This catabolic reaction has always been of keen interest, because it can be exploited for spectroscopic L-carnitine determination in biological fluids – a quantification method, which is developed in our lab – as well as L-carnitine production.Based on a cloned L-CDH sequence an expedition through the currently available prokaryotic genomic sequence space began to mine relevant information about bacterial L-carnitine metabolism hidden in the enormous amount of data stored in public sequence databases. Thus by means of homology-based and context-based protein function prediction is revealed that L-CDH exists in certain eubacterial genomes either as a protein of approximately 35 kDa or as a homologous fusion protein of approximately 54 kDa with an additional putative domain, which is predicted to possess a thioesterase activity. These two variants of the enzyme are found on one hand in the genome sequence of bacterial species, which were previously reported to decompose L-carnitine, and on the other hand in gram-positive bacteria, which were not known to express L-CDH. Furthermore we could not only discover that L-CDH is located in a conserved genetic entity, which genes are very likely involved in this L-carnitine catabolic pathway, but also pinpoint the exact genomic sequence position of several other enzymes, which play an essential role in the bacterial metabolism of L-carnitine precursors.     

Editorial

The complexity and polyfunctionality of carbohydrates as a testing ground for modern organic methodology, carbohydrates as building blocks, carbohydrate related mimetics of natural products as enzyme probes, diagnostics, and therapeutics, carbohydrates in material sciences, all these and many more exciting topics demonstrate this lasting boom in glycosciences. Not many other areas are as rich in complexity, subtle reactivity differences, unusual behaviour of compounds and, as a result, so full of challenges, surprises, and rewards. Consequently, it was a great pleasure to accept the proposal by the Managing Editor of the Austrian journal Chemical Monthly, Prof. Heinz Falk, to compile a representative survey of timely research contributed by international leaders in the field as well as by outstanding young talents. This collection is intended to give evidence for the statements made above as well as to provide informative and entertaining reading for the many who are interested in our field, from advanced students to seasoned researchers. The topic span from an interesting and wide range of contributions in the section synthetic methodology to important subunits of biologically significant lipopolysaccharides, sugar, and nucleoside mimetics and their biological activities as well as applications of saccharides as scaffolds for compound libraries and the application of carbohydrates as chiral auxiliaries. This special issue of Chemical Monthly features four invited reviews: B. La Ferla has surveyed applications of lipases and esterases in selective biocatalytic carbohydrate protection and deprotection reactions. F. Nicotra and his group have exploited carbohydrates as scaffolds for library generation. The liberation of carbonyl functions from C-nitro groups in sugars, an important step in the chain extension of sugars, has been treated by L. Petruš and coworkers. Last but not least, T. M. Wrodnigg has provided a review on important pyrrolidine-related iminoalditols, their natural sources, synthetic approaches, and glycosidase inhibitory activities. In the article section, K. Dax and coworkers have elaborated a system to categorize reactions occurring during attempted nucleophilic displacement reactions at C-2 of pyranosides with diethylaminosulfur trifluoride. A. Fairbanks and his group describe an interesting intramolecular aglycon delivery approach employing allyl protecting groups. R. Madsen and colleagues have taken advantage of a transition metal mediated fragmentation of 6-deoxyiodo glycopyranosides leading to key intermediates for RCM methodology and other approaches to natural products and analogues. T. Lindhorst and M. Walter observed differences in kinetics during a “reactivity tournament” of sugar derived isothiocyanates. Carbohydrate photochemistry, exemplified by transformations of levoglucosan imides to nitrogen containing heterocycles, is reported by J. Thiem and coworkers. In the carbohydrate mimetics section, an account on nucleoside analogues and their biological activities was contributed by the M. Jung group. Thiosugars are the topics in both the contributions by S. Witczak and collaborators and W. Schmid and coworkers. R.V. Stick and A. G. Watts have chased and discussed common features in the mechanistic principles of retaining glycosyl hydrolases and retaining glycosyl transferases. Some new xyloside mimetics related to 1,5-dideoxy-1,5-iminoxylitol were probed as reversible inhibitors of β-xylosidases by S. G. Withers and collaborators. Immunoligically interesting sub-units of chlamydial lipopolysaccharides have been prepared by P. Kosma and coworkers. H. Kunz and colleagues took advantage of carbohydrates as chiral auxiliaries in their synthetic work on tetrahydroquinoline alkaloids. Application of modern NMR spectroscopy is demonstrated by H. K?hlig and coauthors who employed diffusion difference NMR spectroscopy for the analysis of carbohydrate mixtures. It is a special feeling to find so much appreciation for our ‘trade’ here in Austria; we, the guest editors, would like to thank Heinz Falk and Hermann Kalchhauser as well as the Springer publishing team for their kind support, patience, and help with this project. We hope that the readers will enjoy this collection of timely topics in carbohydrate chemistry. Walther Schmid Arnold E. Stütz Issue Editors     

Direct Alkylation of Amines with Primary and Secondary Alcohols through Biocatalytic Hydrogen Borrowing

The reductive aminase from Aspergillus oryzae (Asp RedAm) was combined with a single alcohol dehydrogenase (either metagenomic ADH‐150, an ADH from Sphingobium yanoikuyae (SyADH), or a variant of the ADH from Thermoanaerobacter ethanolicus (Te SADH W110A)) in a redox‐neutral cascade for the biocatalytic alkylation of amines using primary and secondary alcohols. Aliphatic and aromatic secondary amines were obtained in up to 99 % conversion, as well as chiral amines directly from the racemic alcohol precursors in up to >97 % ee , releasing water as the only byproduct.     

TCP Building Blocks for Oligosaccharide Synthesis: Progress Towards the Synthesis of Nodulation Factors

Abstract

The ability of tetrachlorphthaloyl (TCP) sugars to act as glycosyl acceptors as well as the viability of TCP as a global amine protecting group in the syntheis of polyglucosamine natural products such as N-methyl-N-lipid nodulation factors have been examined. Disaccharides corresponding to the reducing end segments and the core region of the target nodulation factors were assembled from n-pentenlyl glycosides. TCP acceptors were successfully coupled with a variety of pentenyl glycosyl donors to produce β-(1→4) oligosaccharides in good yields. Model coupling reactions to produce trisaccharides provided clear evidence for the disarming effect of an ester at O3 on a C4-OH in the glycosyl acceptor. Also, a unique pentenyl donor, which contained the desired N-metyl-N-lipid moiety of the non-reducing end segments of the target compounds, was synthesized and its efficacy in a coupling reaction was tested.     

Graphs to chemical structures. 4: Combinatorial enumeration of planted three-dimensional trees as stereochemical models of monosubstituted alkanes

Planted three-dimensional (3D) trees, which are defined as a 3D version of planted trees, are enumerated by means of Fujita’s proligand method formulated in Parts 1–3 of this series [Fujita in Theor Chem Acc 113:73–79, 80–86, 2005; Fujita in Theor Chem Acc 115:37–53, 2006]. By starting from the concepts of proligand and promolecule introduced previously [Fujita in Tetrahedron 47:31–46, 1991], a planted promolecule is defined as a 3D object in which the substitution positions of a given 3D skeleton are occupied by a root and proligands. Then, such planted promolecules are introduced as models of planted 3D-trees. Because each of the proligands in a given planted promolecule is regarded as another intermediate planted promolecule in a nested fashion, the given planted promolecule is recursively constructed by a set of such intermediates planted promolecules. The recursive nature of such intermediate planted promolecules is used to derive generating functions for enumerating planted promolecules or planted 3D-trees. The generating functions are based on cycle indices with chirality fittingness (CI-CFs), which are composed of three kinds of sphericity indices (SIs), i.e., a _d for homospheric cycles, c _d for enantiospheric cycles, and b _d for hemispheric cycles. For the purpose of evaluating c _d recursively, the concept of diploid is proposed, where the nested nature of c _d is demonstrated clearly. The SIs are applied to derive functional equations for recursive calculations, i.e., a(x), c(x ²), and b(x). Thereby, planted 3D-trees or equivalently monosubstituted alkanes as stereoisomers are enumerated recursively by counting planted promolecules. The resulting values are collected up to 20 carbon content in a tabular form. Now, the enumeration problem initiated by mathematician Cayley [Philos Mag 47(4):444–446, 1874] has been solved in such a systematic and integrated manner as satisfying both mathematical and chemical requirements.     

Growth kinetics of solvent crazes in glassy polymers

The kinetics of craze growth from sharp cracks in polystyrene (PS) and poly(methyl methacrylate) (PMMA) in contact with liquid methanol were measured with time-lapse photography as a function of the stress intensity factor K_I. At high K_I the craze length in both systems increases as √t if the sides of the craze are protected from methanol and as t if they are not, where t is the elapsed time after loading. If such a side-protected craze is dried under load and then methanol is reintroduced to the crack tip, the methanol front advances with the same kinetics as the original craze growth. This experiment Proves that solvent crazing velocities are limited by the hydrodynamic transport of solvent through the porous craze structure under a capillary pressure driving force (which can be as high as 100 atm). An improved model of fluid flow through the craze is developed and shown to predict craze growth kinetics in good agreement with those observed. The hydraulic permeability of methanol crazes in PS was found to be independent of craze length at small craze length and to be independent of K_I except at very low K_I. Although increases in molecular weight in the range M_w = 200,000 to M_w = 670,000 do not markedly affect the crazing kinetics, they greatly increase the time to fracture of the craze.     

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

The zwitterionic–biradical tetramethylene proposed by Huisgen as the key intermediate in stepwise [2+2] cycloaddition reactions has been shown to be the crucial intermediate in spontaneous vinyl polymerizations as well. Predominantly biradical tetramethylenes initiate free‐radical copolymerizations, while predominantly zwitterionic tetramethylenes initiate cationic or anionic homopolymerizations. Stepwise cycloaddition is viewed as a spontaneous polymerization lacking a propagation step. These tendencies could be correlated in the form of an ‘organic chemist's Periodic Table’, which has recently been put on a quantitative basis. Huisgen also showed experimentally that [4+2] Woodward–Hoffman‐allowed cycloadditions are completely concerted. Spontaneous copolymerizations accompanying these cycloadditions, therefore, were ascribed to the s‐trans diene form. This concept was given support by kinetics studies, as well as by exclusive cycloaddition from s‐cis cyclopentadiene, and exclusive copolymerization from s‐trans verbenene.     

Addition Reactions of Glycal Esters: Access to Glycosyl Donors of Kdo,d-glycero-d-talo- and d-glycero-d-galacto-2-Octulosonic Acid Residues

ABSTRACT

Addition reactions of O-acetylated glycal esters of Kdo mono-, α-(2→8)- and α-(2→4)- linked Kdo disaccharide derivatives 1a - c with NIS in acetic acid afforded good yields of trans-diaxial as well as minor amounts of trans-diequatorial and cis-configured 2-O-acetyl-3-deoxy-3-iodo derivatives, which were efficiently reduced with Bu₃SnH/AIBN to give the corresponding per-O-acetylated Kdo methyl ester derivatives. Similar reactions of 1a with NBS or NCS furnished the trans-diaxial 2-O-acetyl-3-bromo-3-deoxy- as well as 3-chloro-3-deoxy derivatives as the main products. Reaction of 1a with NBS in aqueous MeCN provided the 2,3-trans-bromohydrin derivative 11c, which upon treatment with DBU in MeCN gave the elimination product 11 and the α-2,3-anhydro derivative 12 as a suitable donor of glycosides with D-glycero-D-talo- or D-glycero-D-galacto configuration, respectively.     

Polymerization of α-methylstyrene by n-butyllithium in tetrahydrofuran

The kinetics of polymerization of α-methylstyrene by n-BuLi (labeled with C¹⁴ and unlabeled) has been studied in tetrahydrofuran at ?78°C. The catalyst n-BuLi was used as a complex of n-BuLi in THF and a hexane solution of n-BuLi. Contrary to expectations, the relative polymerization rate and the catalyst consumption were higher when a hexane solution of n-BuLi was used. Experimental molecular weights of the polymers greatly exceeded those calculated for the case of complete catalyst consumption. The polymers exhibited low polydispersity, and when a hexane solution of n-BuLi was used, the molecular weight distribution was bimodal. The rate of initiation for the case of polymerization α-methylstyrene with a hexane solution of n-BuLi as a catalyst was much higher than in the polymerization of α-methylstyrene with the use of the complex of n-BuLi in THF as in situ catalyst. Experimental data confirm the preferable interaction of α-methylstyrene with associated n-BuLi in the presence of THF. The complex which was formed as a result of such interaction is an active centers of polymerization.     

Synthesis of aromatic polyesters and polyamides by alternating copolymerizations of 1,4-dicarbonyl-1,4-dihydronaphthalene with bezoquinones and benzoquinone diimines

1,4-Dicarbonyl-1,4-dihydronaphthalene ( 1 ) was synthesized by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride with triethylamine and obtained as its very dilute solution, but it easily polymerized in the concentration as high as 0.1 mol/L to give its polymer. 1 generated in situ by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride in a deoxygenated toluene polymerized alternatingly with benzoquinones such as 2-dodecylthio-p-benzoquinone, 2,5-di(tert-butyl)-p-benzoquinone, p-benzoquinone, and 2,3-dichloro-5,6-dicyano-p-benzoquinone, and with benzoquinone diimines such as N,N′-diethoxycarbonyl-p-benzoquinone diimine, N,N′-dibenzoyl-p-benzoquinone diimine, and N,N′-diphenyl-p-benzoquinone diimine to give aromatic polyesters and polyamides, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1929–1936, 1998     

Formation of Heptaleno[1,2-c]furans and Heptaleno[1,2-c]furanones

The dehydrogenation reaction of the heptalene-4,5-dimethanols 4a and 4d , which do not undergo the double-bond-shift (DBS) process at ambient temperature, with basic MnO₂ in CH₂Cl₂ at room temperature, leads to the formation of the corresponding heptaleno[1,2-c]furans 6a and 6d , respectively, as well as to the corresponding heptaleno[1,2-c]furan-3-ones 7a and 7d , respectively (cf. Scheme 2 and 8). The formation of both product types necessarily involves a DBS process (cf. Scheme 7). The dehydrogenation reaction of the DBS isomer of 4a , i.e., 5a , with MnO₂ in CH₂Cl₂ at room temperature results, in addition to 6a and 7a , in the formation of the heptaleno[1,2-c]-furan-1-one 8a and, in small amounts, of the heptalene-4,5-dicarbaldehyde 9a (cf. Scheme 3). The benzo[a]heptalene-6,7-dimethanol 4c with a fixed position of the C?C bonds of the heptalene skeleton, on dehydrogenation with MnO₂ in CH₂Cl₂, gives only the corresponding furanone 11b (Scheme 4). By [²H₂]-labelling of the methanol function at C(7), it could be shown that the furanone formation takes place at the stage of the corresponding lactol [3-²H₂]- 15b (cf. Scheme 6). Heptalene-1,2-dimethanols 4c and 4e , which are, at room temperature, in thermal equilibrium with their corresponding DBS forms 5c and 5e , respectively, are dehydrogenated by MnO₂ in CH₂Cl₂ to give the corresponding heptaleno[1,2-c]furans 6c and 6e as well as the heptaleno[1,2-c]furan-3-ones 7c and 7e and, again, in small amounts, the heptaleno[1,2-c]furan-1-ones 8c and 8e , respectively (cf. Scheme 8). Therefore, it seems that the heptalene-1,2-dimethanols are responsible for the formation of the furan-1-ones (cf. Scheme 7). The methylenation of the furan-3-ones 7a and 7e with Tebbe's reagent leads to the formation of the 3-methyl-substituted heptaleno[1,2-c]furans 23a and 23e , respectively (cf. Scheme 9). The heptaleno[1,2-c]furans 6a, 6d , and 23a can be resolved into their antipodes on a Chiralcel OD column. The (P)-configuration is assigned to the heptaleno[1,2-c]furans showing a negative Cotton effect at ca. 320 nm in the CD spectrum in hexane (cf. Figs. 3–5 as well as Table 7). The (P)-configuration of (–)- 6a is correlated with the established (P)-configuration of the dimethanol (–)- 5a via dehydrogenation with MnO₂. The degree of twisting of the heptalene skeleton of 6 and 23 is determined by the Me-substitution pattern (cf. Table 9). The larger the heptalene gauche torsion angles are, the more hypsochromically shifted is the heptalene absorption band above 300 nm (cf. Table 7 and 8, as well as Figs. 6–9).