Enantioselective Total Synthesis of (+)-Eutypoxide B

A Strategy for the Convergent and Stereoselective Assembly of Polycyclic Molecules

The stereoselective oxidative coupling of cyclic ketones via silyl bis-enol ethers followed by ring-closing metathesis is shown to be a general and powerful reaction sequence for the preparation of diverse polycyclic scaffolds from simple precursors. The modular strategy successfully constructs substructures prevalent in numerous bioactive natural product families, varying in substitution and carbocyclic composition. Several of the prepared compounds were shown to possess potent cytotoxic activity against a panel of tumor cell lines. The utility of this strategy was further demonstrated by a concise and highly convergent 17-step formal synthesis of the complex antimalarial marine diterpene, (+)-7,20-diisocyanoadociane.

Use of aziridines for the stereocontrolled synthesis of (-)-LL-C10037α, (+)-MT35214, and (+)-4-epi-MT35214

Strategies for the synthesis of the title compounds have been developed using a diastereoselective aziridination reaction of 4-O-substituted cyclohexenones. Aziridination using a chiral amine permitted resolution of a 4-hydroxycyclohexane derivative, and this resulted in the synthesis of both enantiomers of the title compound. Alternatively, the chiral 4-hydroxycyclohexenone starting material was derived from quinic acid. In both cases stereoselective epoxidation and opening of the aziridine ring with hydrazoic acid afforded the 2-azidocyclohexenone, which was transformed to the 2-acetamido group present in the natural product.

Absolute Configuration of Natural Cyclohexene Oxides by Time Dependent Density Functional Theory Calculation of the Optical Rotation: The Absolute Configuration of (−)-Sphaeropsidone and (−)-Episphaeropsidone Revised

The optical rotatory power of some natural cyclohexene oxides, such as (+)-chaloxone, 1, (+)-epiepoformine, 2, (+)-epoformine, 3, (+)-epoxidone, 5, (-)-sphaeropsidone, 6, (-)-episphaeropsidone, 7, and the synthetic compound (+)-epitheobroxide, 4, has been calculated by means of the TDDFT/B3LYP method using the 6-31G(d) and aug-cc-pVDZ basis sets, both in the gas phase and in solution by means of the polarizable continuum model. For compounds 1 and 2, which possess high (about 300 units) optical rotations, gas-phase calculations with the smaller basis set are able to reproduce the experimental values both in sign and order of magnitude. By contrast, a larger basis set is required to satisfactorily simulate the OR values of 3 and 4, which show smaller (about 100 units or less) rotations. The inclusion of the solvent effects is different for different compounds; for 1 and 2, it leads to a better agreement between experiment and prediction, while for 3 and 4, the presence of hydrogen bonding groups makes the application of continuum solvation models less satisfactory. For the flexible system 5, the absolute configuration could not be determined using gas-phase calculations and the smaller basis set, but both inclusion of solvent and larger basis set effects are compulsory. It is noteworthy that calculations both in the gas phase and in the solvent lead to a positive rotatory power for the laevorotatory natural compounds 6 and 7 if the ACs reported in the literature are employed to do the theoretical prediction. This strongly indicates that the ACs previously assigned to these compounds in the literature are not correct and that the TDDFT prediction of OR values has become by now a practicable tool for AC assignments.

Metabolites from Eutypa species that are pathogens on grapes

Structural and synthetic studies of the metabolites isolated from Eutypa lata are reviewed. This fungus is the causative agent of Eutypa dieback disease, also known as eutyposis or dying-arm disease, a perennial canker that affects grapevines and many other woody fruit plants. The review, which encompasses all the literature in this field up to the present and in which 76 references are cited, also includes a detailed study of the biological activity of the metabolites, especially the role of toxins in the development of the plant disease. Some aspects of the synthesis and biosynthesis of these metabolites and related compounds are discussed.

Aziridines as a Protecting and Directing Group. Stereoselective Synthesis of (+)-Bromoxone

[reaction: see text] The directing ability of an aziridine group for the epoxidation of adjacent double bonds is demonstrated. The aziridine group is also used to effectively protect a double bond in a cycloenone system for a short synthesis of the title compound.

Synthesis of anellated carbasugars from (--)-quinic acid

(3R,4R,5R)-3-[(tert-Butyl-dimethylsilyl)oxy]-4,5-(isopropylidenedioxy)-1-cyclohexanone (2) reacted with carbon disulfide and methyl iodide in the presence of sodium hydride to furnish (3R,4R,5R)-5-[(tert-butyl-dimethylsilyl)oxy]-3,4-(isopropylidenedioxy)-2-[bis(methylthio)methylene]-1-cyclohexanone (3). 2 and N,N-dimethylformamide dimethyl acetal afforded (2E,3R,4R,5R)-5-[(tert-butyl-dimethylsilyl)oxy]-2-(dimethylaminomethylene)-3,4-(isopropylidenedioxy)-1-cyclohexanone (4). These push-pull activated methylenecyclohexanones 3 and 4 underwent a ring closure reaction with hydrazine hydrate and methylhydrazine, respectively, to give pyrazoloanellated carbasugars. Treatment of 3 with formamidinium, acetamidinium and benzamidinium salts, respectively, in the presence of sodium methanolate yielded three (5R,6R,7R)-7-[(tert-butyl-dimethylsilyl)oxy]-5,6,7,8-tetrahydro-5,6-(isopropylidenedioxy)benzo[d]pyrimidines.