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1.
An advanced metabolite, named premalbrancheamide, involved in the biosynthesis of malbrancheamide (1) and malbrancheamide B (2) has been synthesized in double (13)C-labeled form and was incorporated into the indole alkaloid 2 by Malbranchea aurantiaca. In addition, premalbrancheamide has been detected as a natural metabolite in cultures of M. aurantiaca. The biosynthetic implications of these experiments are discussed.  相似文献   

2.
The biomimetic total syntheses of both malbrancheamide and malbrancheamide B are reported. The synthesis of the two monochloro species enabled the structure of malbrancheamide B to be unambiguously assigned. The syntheses each feature an intramolecular Diels-Alder reaction of a 5-hydroxypyrazin-2(1H)-one to construct the bicyclo[2.2.2]diazaoctane core, which has also been proposed as the biosynthetic route to these compounds.  相似文献   

3.
Cucubaldiol ( 1 ), a novel norsesquiterpenoid incorporating a bicyclo[2.2.2]octene ring system, was isolated from the whole plants of Cucubalus baccifer L. Its structure was determined on the basis of spectroscopic data especially by 2D‐NMR and X‐ray diffraction analyses.  相似文献   

4.
The gas phase thermal reactions exhibited by bicyclo[4.2.0]oct-2-ene and 7-d and 8-d analogues at 300 degrees C have been followed kinetically through GC and 2H NMR spectroscopic analyses. In contrast to the pattern of transformations exhibited by bicyclo[3.2.0]hept-2-ene and deuterium-labeled analogues, no reactions initiated by C1-C6 bond cleavage are seen, epimerization at C8 is much faster than [1,3] shifts leading to bicyclo[2.2.2]oct-2-ene, and the ratio of rate constants for [1,3] carbon migration with inversion versus migration with retention is approximately 1.4. Homolysis of C1-C8 to give a conformationally flexible diradical intermediate having a relatively long lifetime and multiple options for further reaction (re-formation of C1-C8 with or without net epimerization, fragmentation to 1,3-cyclohexadiene and ethylene, migration to the original C3 with inversion or retention) accords well with the observations. Clearly, orbital symmetry control does not govern stereochemistry for the [1,3] sigmatropic carbon shifts.  相似文献   

5.
A convergent and efficient formal synthesis of (±)-atisine has been accomplished. The synthetic strategy is to efficiently construct the bicyclo[2.2.2]octane ring moiety by an oxidative dearomatization/intramolecular Diels-Alder cycloaddition cascade. The first total synthesis of another atisine-type C(20)-diterpenoid alkaloid, (±)-isoazitine, has also been achieved employing the same strategy.  相似文献   

6.
Sacher JR  Weinreb SM 《Organic letters》2012,14(8):2172-2175
An efficient synthetic strategy has been developed for annulation of an azocane ring onto a bicyclo[2.2.2]octane scaffold via an intramolecular hydroaminomethylation protocol to generate an advanced intermediate bearing three of the four rings of the structurally unique Lycopodium alkaloid lycopladine H (1).  相似文献   

7.
Polyesters containing bicyclo[2.2.2]octane and bicyclo[3.2.2]nonane rings are prepared from 1,4-bis(carboethoxy)bicyclo[2.2.2]octane, 1,4-bis(hydroxymethyl)bicyclo[2.2.2]-octane and the 1,5-disubstituted bicyclo[3.2.2]nonane analogs. These polyesters are compared to the related polymers containing 1,4-phenylene and trans-1,4-cyclohexylene rings in terms of their melting point, thermal stabilities and oxidative stabilities. The lower symmetry of the bicyclo[3.2.2]nonane ring produces lower-melting polymers than the other ring systems. The remaining three rings are approximately equivalent in their effect on the melting point of a polymer provided that no more than one bicyclo[2.2.2]octane ring is present per polymer repeat unit. Two such rings produce a highermelting polymer than any other combination. Both the thermal and oxidative stabilities of the polyesters is improved by the presence of the bicyclo rings. This is attributed to the rings providing an approximation of a ladder polymer.  相似文献   

8.
The acidities of 3- and 4-substituted bicyclooctane-1-carboxylic acids and 3-substituted bicyclo[1.1.1]pentane-1-carboxylic acids have been calculated at the MP2/6-311++G** theoretical level. There is good agreement between the calculated and observed gas-phase acidities. The acidities of the 4-substituted bicyclooctane acids were found to be linearly dependent on the C-X bond dipoles, as expected from a field effect. The substituents had a negligible effect on the electron density at C1. The difference in acidity between 4-chlorobicyclo[2.2.2]octane-1-carboxylic acid and the parent acid (6.2 kcal/mol) is reproduced by the Kirkwood-Westheimer treatment of substituent effects on acidity, but only if the bicyclooctane ring is given an effective dielectric constant of unity. The acidities of the 3-substituted bicyclooctane acids are linearly related to the corresponding 4-substituted acids with a slope of 0.9. The acidities of the 3-substituted bicyclo[1.1.1]pentane-1-carboxylic acids are linearly related to the C-X bond dipoles for this ring system (which are different than those for the bicyclooctanes), and they are also linearly related to the acidity of the 4-substituted bicyclo[2.2.2]octanecarboxylic acids with a slope of 1.34. The larger slope is due to the smaller bridgehead-bridgehead distance in the bicyclopentane ring than in bicyclo[2.2.2]octane.  相似文献   

9.
The synthesis of the novel bicyclo[2.2.2]octanyl[1,4]benzodiazepinone ring system (IV) and its facile acid catalysed rearrangement to the corresponding bicyclo[2.2.2]oct-2-enylbenzirnid-azole system (IX) is described.  相似文献   

10.
The synthesis of 4-triflyloxy-2,6,6-trimethyl-2,4-cyclohexadienone (13), bicyclo[2.2.2]octenones 1a-j and 15a-j, and bicyclo[2.2.2]octadienones 2a-f, 6a-d, and 11a-f is described. The 2,4-cyclohexadienones 4 and 13 were used for the first time as nondimerizing and easily accessible alternatives to 2,6,6-trimethyl-2,4-cyclohexadienone 12 in Diels-Alder reactions with acetylene derivatives 5a-d to prepare the adducts 6a-d and 11a-e in excellent yields. Compounds 11a-d were initially prepared by the alcoholysis of 6a-d to afford bicyclo[2.2.2]octene-2,5-diones 7a-dfollowed by treatment of 7a-d with N-phenyltriflimide in the presence of LHMDS at -78 degrees C. Diels-Alder reaction of 13 with an acetylene equivalent, phenyl vinyl sulfoxide, was also studied. A detailed study of the Diels-Alder reactions of various olefinic dienophiles 14a-j with 13 has been carried out to furnish cycloadducts 15a-j in high yields. Reductive removal of triflyloxy group of vinyl triflates 11a-f and 15a-j was performed in the presence of [Pd(PPh(3))(2)Cl(2)-Bu(3)N-HCO(2)H] to obtain the desired bicyclo[2.2.2]octadienones 2a-f and bicyclo[2.2.2]octenones 1a-j, respectively, in good overall yields.  相似文献   

11.
The transmission of polar effects through the bicyclo[2.2.2]octane framework has been investigated by ascertaining how the geometry of a phenyl group at a bridgehead position is affected by a variable substituent at the opposite bridgehead position. We have determined the molecular structure of several Ph-C(CH(2)-CH(2))(3)C-X molecules (where X is a charged or dipolar substituent) from HF/6-31G and B3LYP/6-311++G molecular orbital calculations and have progressively replaced each of the three -CH(2)-CH(2)- bridges by a pair of hydrogen atoms. Thus the bicyclo[2.2.2]octane derivatives were changed first into cyclohexane derivatives in the boat conformation, then into n-butane derivatives in the anti-syn-anti conformation, and eventually into assemblies of two molecules, Ph-CH(3) and CH(3)-X, appropriately oriented and kept at a fixed distance. For each variable substituent the deformation of the benzene ring relative to X = H remains substantially the same even when the substituent and the phenyl group are no longer connected by covalent bonds. This provides unequivocal evidence that long-range polar effects in bicyclo[2.2.2]octane derivatives are actually field effects, being transmitted through space rather than through bonds. Varying the substituent X in a series of Ph-C(CH(2)-CH(2))(3)C-X molecules gives rise to geometrical variation (relative to X = H) not only in the benzene ring but also in the bicyclo[2.2.2]octane cage. The two deformations are poorly correlated. The rather small deformation of the benzene ring correlates well with traditional measures of long-range polar effects in bicyclo[2.2.2]octane derivatives, such as sigma(F) or sigma(I) values. The much larger deformation of the bicyclo[2.2.2]octane cage is controlled primarily by the electronegativity of X, similar to deformation of the benzene ring in Ph-X molecules. Thus the field and electronegativity effects of the substituent are well separated and can be studied simultaneously, as they act on different parts of the molecular skeleton.  相似文献   

12.
Fluorene 1 fully annelated with bicyclo[2.2.2]octene units was newly synthesized and oxidized to stable cationic species. The structure of radical cation salt 1(.+)SbCl(6)(-) was determined by X-ray crystallography, while the first fluorene dication 1(2+) was characterized by (1)H and (13)C NMR at -80 degrees C. Combined with the results of theoretical calculations, an important contribution of a quinoidal structure to the resonance hybrid was demonstrated in both 1(.+) and 1(2+). [structure: see text]  相似文献   

13.
The insulating role of the bicyclo[2.2.2]octane fragment has been theoretically evaluated by comparing the electronic coupling parameter (V(ab)) in 1,4-bis(ferrocenyl)benzene (1) and 1,4-bis(ferrocenyl)bicyclo[2.2.2]octane (2). The geometries were optimized by DFT and an extended Hückel calculation was performed to evaluate V(ab) by the dimer splitting method. The calculations showed a 12-fold decrease of the electronic coupling from 60 meV for 1 to 5 meV for 2. The second part describes the synthesis of two potential molecular motors with one incorporating the insulating bicyclo[2.2.2]octane fragment. These molecules are based on a ruthenium complex bearing a tripodal stator functionalized to be anchored onto surfaces. The ferrocenyl electroactive groups and the cyclopentadienyl (Cp) rotor are connected through a p-phenylene spacer (5) or through a spacer incorporating an insulating bicyclo[2.2.2]octane moiety (6).  相似文献   

14.
Seven new prenylated indole alkaloids, taichunamides A–G, were isolated from the fungus Aspergillus taichungensis (IBT 19404). Taichunamides A and B contained an azetidine and 4‐pyridone units, respectively, and are likely biosynthesized from notoamide S via (+)‐6‐epi‐stephacidin A. Taichunamides C and D contain endoperoxide and methylsulfonyl units, respectively. This fungus produced indole alkaloids containing an anti‐bicyclo[2.2.2]diazaoctane core, whereas A. protuberus and A. amoenus produced congeners with a syn‐bicyclo[2.2.2]diazaoctane core. Plausible biosynthetic pathways to access these cores within the three species likely arise from an intramolecular hetero Diels–Alder reaction.  相似文献   

15.
Notoamides produced by Aspergillus spp. bearing the bicyclo[2.2.2]diazaoctane core structure with unusual structural diversity represent a compelling system to understand the biosynthesis of fungal prenylated indole alkaloids. Herein, we report the in vitro characterization of NotB, which catalyzes the indole 2,3-oxidation of notoamide E (13), leading to notoamides C (11) and D (12) through an apparent pinacol-like rearrangement. This unique enzymatic reaction with high substrate specificity, together with the information derived from precursor incorporation experiments using [(13)C](2)-[(15)N](2) quadruply labeled notoamide S (10), demonstrates 10 as a pivotal branching point in notoamide biosynthesis.  相似文献   

16.
17.
Three diprenylated indole alkaloids, mangrovamides A–C (13), featured a bicyclo [2.2.2] diazaoctane core and possessed a novel γ-methyl proline and isoprene derived dimethyl γ-pyrone functionalities hitherto unknown among the family of paraherquamides, were isolated from the fungus Penicillium sp., which was separated from a mangrove soil sample. The structures were elucidated based on NMR, X-ray, and CD methods. The possible biosynthetic pathway of these compounds is proposed.  相似文献   

18.
Nishinaga T  Uto T  Komatsu K 《Organic letters》2004,6(24):4611-4613
A novel cyclooctatetraene (COT) radical cation fully annelated with bicyclo[2.1.1]hexene units was prepared as SbCl(6)(-) salt, and planarity of the octagonal ring was clarified by ESR and theoretical calculations. Its longest wavelength absorption (630 nm) is blue-shifted from that (745 nm) of COT radical cation annelated with bicyclo[2.2.2]octene units due to the widening of the HOMO-SOMO gap accompanying the flattening of the COT ring. [structure: see text]  相似文献   

19.
all-endo-3-amino-5-hydroxybicyclo[2.2.2]octane-2-carboxylic acid (13) and all-endo-5-amino-6-(hydroxymethyl)bicyclo[2.2.2]octan-2-ol (10) were prepared via dihydro-1,3-oxazine or g-lactone intermediates by the stereoselective functionalization of an N-protected derivative of endo-3-aminobicyclo[2.2.2]oct-5-ene-2-carboxylic acid (2). Ring closure of b-amino ester 4 resulted in tricyclic pyrimidinones 15 and 16. The structures, stereochemistry and relative configurations of the synthesized compounds were determined by IR and NMR.  相似文献   

20.
Hydrazinediium dithiocyanate and α,β-unsaturated ketones give in one-pot reactions 1-thiocarbamoyl-2-pyrazolines and 1-formyl-2-pyrazolines. The syntheses of pyridine-2-thiones, pyrimidine-2-thiones and bicyclo[2.2.2]octan-2-ones from ammonium thiocyanates and ketones by analogous procedures are reviewed. The mechanisms of the ring formations are discussed. Crystal structure analyses of a 1-thiocarbamoyl- and a 1-formyl-2-pyrazoline are given.  相似文献   

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