Preparation and cycloaddition reactions of enantiopure 2-(N-acylamino)-1,3-dienes for the synthesis of octahydroquinoline derivatives

Stille, Suzuki-Miyaura, and Sonogashira cross-coupling reactions were carried out with a glutarimide-derived vinyl phosphate, bearing a chiral auxiliary on the N atom, to prepare enantiopure 2-(N-acylamino)-1,3-dienes as partners in Diels-Alder reactions. The cycloadditions were performed with various dienophiles under thermal conditions, with or without Lewis acids. With maleimides, the preferential formation of endo cycloadducts was observed, whereas with acrylamides the exo approach prevailed. Furthermore, in the latter case, 6-substitued octahydroquinolinones were obtained in accordance with the predicted regioselectivity. Since diastereopure compounds were in all cases obtained either by chromatography or by crystallization, and because of the easy access to a variety of boronic acids, to be used in the coupling step, this methodology is useful for the short synthesis of differently substituted, enantiopure octahydroquinolinones amenable to further transformation into decahydroquinolines possessing interesting biological activities.

Double Addition of Grignard Reagents to N-Glycosyl Nitrones: A New Tool for the Construction of Enantiopure Azaheterocycles

[Reaction: see text] C-Phenyl-N-erythrosylnitrone 3 behaves as a C1,C1' bis-electrophile, undergoing a double addition of Grignard reagents in a domino fashion to afford acyclic hydroxylamines 4. The reaction proceeds at 0 degrees C with variable degrees of diastereoselectivity, from moderate to good, mainly depending on the organomagnesium reagent used. The usefulness of compounds 4 has been exemplified with the synthesis of pyrroloazepine 12 through a ring closing metathesis key step.

Total Synthesis of Bruceolline I

The first total synthesis of the natural product bruceolline I, isolated in small quantities from the ethanol extract of Brucea mollis stems, was achieved in 29% yield over nine steps and with high enantiomeric purity (>98%). The key step of the process is the tandem gold-catalyzed rearrangement/Nazarov reaction of a propargylic acetate derivative. This synthesis provides a sufficient amount of synthesized bruceolline I for further bioassays.

Quasienantiomeric levoglucosenone and isolevoglucosenone allow the parallel kinetic resolution of a racemic nitrone

Cycloadditions of chiral pyrroline N-oxides to levoglucosenone (1) and isolevoglucosenone (2) proceed with a high level of double asymmetric induction. Partial kinetic resolutions (KR) of both enantiomers of a racemic nitrone 3 were achieved, and a parallel kinetic resolution (PKR) experiment allowed the stereoselective divergent synthesis of two quasienantiomeric imino-C-disaccharide precursors.

Design, Synthesis, and Biological Evaluation of New 1-(Aryl-1 H-pyrrolyl)(phenyl)methyl-1 H-imidazole Derivatives as Antiprotozoal Agents

We have designed and synthesized a series of new imidazole-based compounds structurally related to an antiprotozoal agent with nanomolar activity which we identified recently. The new analogues possess micromolar activities against Trypanosoma brucei rhodesiense and Leishmania donovani and nanomolar potency against Plasmodium falciparum. Most of the analogues displayed IC₅₀ within the low nanomolar range against Trypanosoma cruzi, with very high selectivity toward the parasite. Discussion of structure-activity relationships and in vitro biological data for the new compounds are provided against a number of different protozoa. The mechanism of action for the most potent derivatives (5i, 6a-c, and 8b) was assessed by a target-based assay using recombinant T. cruzi CYP51. Bioavailability and efficacy of selected hits were assessed in a T. cruzi mouse model, where 6a and 6b reduced parasitemia in animals >99% following intraperitoneal administration of 25 mg/kg/day dose for 4 consecutive days.

Thiacyclophane Cages and Related Bi- and Tripodal Molecules via Transient Polysulfenic Acids

A series of bis- and tris-bridged thiacyclophane S-oxides, as racemates or meso products, have been synthesized with a new procedure. Starting from the corresponding thiols, in three steps, transient polyarene- and polyarylmethane-sulfenic acids were generated in the presence of di- and triethynylbenzenes. The thermal syn-addition of these sulfenic acids onto the triple bonds of the unsaturated acceptors was conducted in CH2Cl2 at 40 degrees C. The concentration of sulfoxide precursors of sulfenic acid and the sulfoxide/acceptor molar ratio addressed the syn-addition toward open-chain benzene sulfoxides or thiacyclophane S-oxides. Complete stereochemical control was observed in some reactions between polysulfenic acids and ethynylbenzenes, where the meso dithiacyclophane S,S'-dioxides were obtained exclusively, whereas 1:1 mixtures of meso/rac dithiacyclophanes S,S'-dioxides were isolated as products of other reactions. In almost all the cases, the obtained compounds were separated by column chromatography. The structure assignment of the new heterophanes was done on the basis of their diagnostic NMR spectra and X-ray crystallographic analysis of some of them. Open-chain polysulfinyl and polysulfinylmethyl benzenes, obtained as meso/rac mixtures, were separated and the products were fully characterized. Both synthesized cages, including trithia[3(3)](1,3,5)cyclophane S,S',S' '-trioxides, and bi- and tripodal benzene sulfoxides, appear promising in the field of coordination and material chemistry.

Two-step one-pot synthesis of dihydropyrazinones as Xaa-Ser dipeptide isosteres through morpholine acetal rearrangement

The synthesis of the uncommon dihydropyrazinone ring was accomplished by taking advantage of the ring rearrangement ofN-acylated morpholine acetal derived from serine under acidic treatment and in the presence of 2,6-lutidine, resulting in a constrained Xaa-Ser dipeptide isostere.