Giorgio Della Sala

Highly Enantioselective Synthesis of β-Amidophenylthioethers by Organocatalytic Desymmetrization of meso-Aziridines

The desymmetrization of N-acylaziridines with Me(3)SiSPh, catalyzed by commercially available (R) and (S)-VAPOL hydrogen phosphate, produced beta-(N-acylamino)phenylthioethers in a highly enantioselective and efficient manner (78-99% ee). The selection of the suitable aziridine/nucleophile/catalyst molar ratio is crucial to obtain high ees.

A general phosphoric acid-catalyzed desymmetrization of meso-aziridines with silylated selenium nucleophiles

The first example of meso-aziridine desymmetrization with selenium nucleophiles is reported. The reaction, promoted by VAPOL-hydrogen phosphate using (phenylseleno)trimethylsilane as the nucleophile, proves to be very general and highly enantioselective (84-99% ee).

Enantioselective Alkylation of Amino Acid Derivatives Promoted by Cyclic Peptoids under Phase-Transfer Conditions

The effects of substituents and cavity size on catalytic efficiency of proline-rich cyclopeptoids under phase-transfer conditions were studied. High affinity constants (Ka) for the sodium and potassium cations, comparable to those reported for crown ethers, were observed for an alternated N-benzylglycine/L-proline hexameric cyclopeptoid. This compound was found to catalyze the alkylation of N-(diphenylmethylene)glycine cumyl ester in values of enantioselectivities comparable with those reported for the Cinchona alkaloid ammonium salts derivatives (83-96% ee), and with lower catalyst loading (1-2.5% mol), in the presence of a broad range of benzyl, allyl and alkyl halides.

Synthesis of antifungal N-isoprenyl-indole alkaloids from the fungus Aporpium caryae ☆

Abstract The synthesis of two antifungal alkaloids 1 and 2 is described. It involves the N -isoprenyl-indole brominated key-intermediate 3 prepared by introduction of the isoprenyl group on the indole core itself.

Metallocene-Catalyzed Diastereoselective Epoxidation of Allylic Alcohols

Abstract Allylic alcohols undergo an efficient process of diastereoselective epoxidation by t-butyl hydroperoxide (TBHP) in n-hexane solution in the presence of catalytic amounts of mono- and bis-cyclopentadienyl titanium(IV) and zirconium(IV) chlorides.

SYNTHESIS OF CALICOFEROL E AND ASTROGORGIADIOL, TWO MARINE 9,10-SECOSTEROIDS

Abstract The synthesis of two marine 9,10-secosteroids, calicoferol E and astrogorgiadiol, has been achieved starting from vitamin D 3 . The conceived approach establishes a general convergent strategy toward the synthesis of 9,10-secosteroids.

Stereoselective amine-thiourea-catalysed sulfa-Michael/nitroaldol cascade approach to 3,4,5-substituted tetrahydrothiophenes bearing a quaternary stereocenter.

Summary An investigation on the stereoselective cascade sulfa-Michael/aldol reaction of nitroalkenes and commercially available 1,4-dithiane-2,5-diol to 3,4,5-substituted tetrahydrothiophenes, bearing a quaternary stereocenter, is presented. A secondary amine thiourea derived from (R,R)-1,2-diphenylethylamine was found to be the most effective catalyst when using trans-β-methyl-β-nitrostyrenes affording the heterocyclic products in good yields and moderate stereoselectivities.

Diastereoselective oxidation of β-hydroxysulfides with TBHP: a comparative study of titanocenes and Ti(Oi-Pr)4 as catalysts

Abstract Titanocene dichlorides and Ti(Oi-Pr)4 have been used as catalysts for the oxidation with t-butyl hydroperoxide of racemic β-hydroxysulfides having a stereogenic carbon centre in α- or β- position with respect to the sulfur atom. β-Hydroxysulfides were oxidized in high yields to the corresponding sulfoxides, titanocenes being more chemo- and generally more diastereoselective than Ti(Oi-Pr)4. A divergent stereochemical outcome has been observed when using titanocenes or Ti(Oi-Pr)4 in the oxidation of protected β-hydroxy sulfides.

Switchable Diastereoselectivity in the Fluoride-Promoted Vinylogous Mukaiyama–Michael Reaction of 2-[(Trimethylsilyl)oxy]furan Catalyzed by Crown Ethers

The fluoride-promoted vinylogous Mukaiyama-Michael reaction of 2-[(trimethylsilyl)oxy]furan with diverse α,β-unsaturated ketones is described. The TBAF-catalyzed VMMR afforded high anti-diastereoselectivity irrespective of the solvents used. The KF/crown ethers catalytic systems proved to be highly efficient in terms of yields and resulted in a highly diastereoselective unprecedented solvent/catalyst switchable reaction. Anti-adducts were obtained as single diastereomers or with excellent diastereoselectivities when benzo-15-crown-5 in CH2Cl2 was employed. On the other hand, high syn-diastereoselectivities (from 73:27 to 96:4) were achieved by employing dicyclohexane-18-crown-6 in toluene. On the basis of DFT calculations, the catalysts/solvent-dependent switchable diastereoselectivities are proposed to be the result of loose or tight cation-dienolate ion pairs.

Cyclic Peptoids as Mycotoxin Mimics: An Exploration of Their Structural and Biological Properties

Cyclic peptoids have recently emerged as important examples of peptidomimetics for their interesting complexing properties and innate ability to permeate biological barriers. In the present contribution, experimental and theoretical data evidence the intricate conformational and stereochemical properties of five novel hexameric peptoids decorated with N-isopropyl, N-isobutyl, and N-benzyl substituents. Complexation studies by NMR, in the presence of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), theoretical calculations, and single-crystal X-ray analyses indicate that the conformationally stable host/guest metal adducts display architectural ordering comparable to that of the enniatins and beauvericin mycotoxins. Similarly to the natural depsipeptides, the synthetic oligolactam analogues show a correlation between ion transport abilities in artificial liposomes and cytotoxic activity on human cancer cell lines. The reported results demonstrate that the versatile cyclic peptoid scaffold, for its remarkable conformational and complexing properties, can morphologically mimic related natural products and elicit powerful biological activities.