Lucia Chiummiento

A chemical/computational approach to the determination of absolute configuration of flexible and transparent molecules: aliphatic diols as a case study.

By reacting flexible and optically transparent in UV-vis molecules such as 1,2-, syn- and anti-1,3-diols, 1,3-sulfanylalcohols of known absolute configuration (AC) with fluorenone dimethyl acetal, the corresponding ketals are obtained. They are conformationally well-defined (only one conformer in most cases) compounds exhibiting medium-high optical rotation (OR) values, which are independent of the solvent, and electronic circular dichroism (ECD) spectra, which show several (up to five) Cotton effects in the 350-200 nm range due to valence shell pi-->pi* transitions. These features allow simulation of the chiroptical properties of these compounds at the TDDFT/B3LYP/6-31G* level of theory to obtain, using the known ACs of these compounds, a satisfactory reproduction of the OR values (sign and order of magnitude; quantitatively, the predicted values are twice the experimental ones), and a more than satisfactory reproduction of the ECD spectra (sign, intensity, and position of the lowest-energy four Cotton effects) for all the compounds studied. Therefore, this approach can be used to assign the AC of such flexible molecules, in particular, syn-1,3-diols, which are important substrates in organic synthesis and for which nonempirical methods of AC assignment have not been devised so far. Furthermore, since the fluorene chromophore leads to the presence of several Cotton effects from, say, 350 to 200 nm, their correct simulation of sign, intensity, and position is a guarantee of the correct assignment of AC: in this way, ECD spectroscopy gains the same advantages of VCD spectroscopy, that is, the need of reproducing many ECD bands and then a solid guarantee of a correct AC assignment.

A general protocol for the regio high yielding opening of different glycidol derivatives

Abstract Differently protected glycidol derivatives (with Bn, TBDPS, TBS and MPM groups) have been tested for regioselective ring opening with vinylmagnesium bromide in order to obtain useful five-carbon functionalised homoallylic alcohols. Careful choice of the reagents and experimental conditions allowed a general access to important chiral synthons for asymmetric synthesis.

Novel chiral calix[4]arenes by direct asymmetric epoxidation reaction.

We report the first asymmetric synthesis of trans optically active (+) C 2 1,3-bisarylepoxide of calix[4]arene in excellent chemical yield and >99% ee, and its enantiospecific conversion to the corresponding bis-dioxolane.

Stereoselective synthesis of C15C24 and C25C30 fragments of dolabelides

The stereocontrolled synthesis of a C15 C24 fragment of dolabelides is reported. The C19 and C21 hydroxyl-bearing stereocenters were installed using ruthenium-mediated asymmetric hydrogenations of cyclic hemiketal 4 and β-keto ester 7. The C25-C30 portion of dolabelides was prepared as well by ring opening of chiral epoxy alcohol 12 to set up the C27 stereogenic center.

N-(3-Benzo[b]thienyl)iminophosphoranes toward the Synthesis of Benzo[b]thieno[3,2-b]pyridines: Reactivity and Alternative Regioselectivity with α,β-unsaturated Ketones and Aldehydes

Abstract The novel N-(3-benzo[b]thienyl)iminophosphoranes 1b–d react with α,β-unsaturated aldehydes and ketones 2a–e to give varying mixtures of the regioisomeric benzothieno[3,2-b]pyridines 3a–d and 4a–d as a result of preferential attack of either imino nitrogen or α-thienyl carbon at the enone carbonyl group. The findings indicate that the progressive replacement of phenyl with methyl P-substituent greatly enhances the reactivity of the phosphorane 1 and concomitantly enhances the propensity of the phosphorane itself for addition to the enone by the α-thienyl carbon.

Synthesis of new thienyl ring containing HIV-1 protease inhibitors: promising preliminary pharmacological evaluation against recombinant HIV-1 proteases.

A series of new thienyl ring containing analogues of nelfinavir and saquinavir with different substitution patterns were synthesized from suitable enantiopure diols. Their inhibitory activity against wild type recombinant HIV-1 protease was evaluated. In general thienyl groups spaced from the core by a methylene group gave products showing IC(50) in the nanomolar range, irrespective of the type and the substitution pattern of the heterocycle. The range of activity of the two most active compounds is substantially maintained or even increased against two commonly selected mutants, under drug pressure, such as V32I and V82A.

Ring opening of 2,3-epoxy 1-tosylates to halohydrins and subsequent elaboration to asymmetrical alcohols

Abstract 2,3 -epoxy alcohols-1-tosylates are regio and chemoselectively opened to the corresponding 3-halohydrins (I, Br, Cl): the reduction of the iodohydrins to the monoprotected diols and subsequent standard coupling of the tosyl group leads to a straightforward synthesis of optically active naturally occurring pheromones.

Heterocycles in peptidomimetics and pseudopeptides: design and synthesis.

This minireview provides a brief outline of the peculiar aspects of the preparation of peptidomimetic and pseudopeptidic structures containing heterocycles. In particular novel tricyclic structures are investigated as potential drugs.

Synthesis and biological evaluation of novel small non-peptidic HIV-1 PIs: The benzothiophene ring as an effective moiety

Synthesis and biological evaluation of a new series of potential HIV-1 protease inhibitors incorporating different heterocycles are described. The variation of heteroatom in such molecules has displayed totally different biological activities and a benzothiophene containing inhibitor has shown high potency against wild type HIV-1 protease with IC(50)=60 nM, thanks to the lower desolvation penalty to be payed by such hydrophobic moiety.

First enantioselective synthesis of (-)-seiridin the major phytotoxic metabolite of Seiridium species pathogenic for cypress

Abstract the first enantioselective synthesis of seiridin, a phytotoxic dialkylsubstituted butenolide produced by three Seiridium species, fungi pathogenic for cypress, is described. The short sequence, which leads to optically pure compound 1, would be useful to the obtaining of larger quantities of the compound for genetic selection of resistant cypress plants.