Peter Šafář

Use of chiral-pool approach into epi-thieno analogues of the scarce bioactive phenanthroquinolizidine alkaloids

Abstract The stereoselective synthesis of epi-thieno analogues of the phenanthroquinolizidine bioactive alkaloids (−)-Cryptopleurine and (−)-(15R)-Hydroxycryptopleurine was achieved in five steps starting from easily available enantiopure (S)-2-aminoadipic acid used as chiral pool and nitrogen atom source. During these investigations, both π-cationic cyclization of chiral N-thienylmethyl-6-oxopipecolinic acids into pure (S)-keto-lactams and theirs regioselective and diastereoselective reduction, considered as key steps of this sequence, were studied. Of particular interest, the Friedel–Crafts cyclization using (CF3CO)2O/BF3·Et2O show that near the expected keto-lactams, enamides and enamidones containing trifluoromethyl residue were isolated. A mechanism leading to the latter products with high synthetic potential was discussed.

Structure and Mechanism Revision of a Catalyzed Cyclization of Benzaldehyde Bearing Alkyne-Nitrile

Pt(II)-catalyzed carbocyclization of benzaldehyde containing a keto-nitrile functionality resulted in the formation, respectively, of isochromenes and spiro-lactones instead of fused lactams and spiro-lactams as was previously reported. The reaction mechanism was proposed, and the products were identified by multidimensional NMR, IR, and X-ray analysis. The structure of these new products was also confirmed by their synthesis in an unambiguous manner using practical and short approaches.

(8aS)-7,8,8a,9-Tetra-hydro-thieno[3,2-f]indolizin-6(4H)-one.

In the molecular structure of the title compound, C10H11NOS, the central six-membered ring of the indolizine unit adopts an envelope conformation, the maximum deviations from the mean plane of the ring being 0.533 (2) Å. The fused thieno ring is nearly coplanar [mean deviation = 0.007 (2) Å]. The conformation of the fused oxopyrrolidine ring is close to that of a flat-envelope, with a maximum deviation of 0.339 (3) Å. The crystal structure is stabilized by C—H⋯O hydrogen bonds.

(11R,11aS)-11-Hydr-oxy-1,5,11,11a-tetra-hydro-1-benzothieno[2,3-f]indolizin-3(2H)-one.

The absolute configuration of the title compound, C14H13NO2S, was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine system adopts an envelope conformation, the greatest deviation from the mean plane of the ring being 0.459 (2) Å for the N atom. The benzothieno system is planar [mean deviation = 0.009 (2) Å]. In the crystal structure, molecules form chains parallel to the b axis via intermolecular O—H⋯O hydrogen bonds.

Antimicrobial activity of newly synthesized thienoquinolizidines derivatives: inspired by natural plant alkaloids

The antimicrobial activity of 16 newly prepared quinolizidines derivatives using bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Proteus sp., Escherichia coli) acid fast bacterium Mycobacterium smegmatis, yeasts (Candida albicans, Candida parapsilosis), and filamentous fungi (Fusarium culmorum, Microsporum gypseum, Aspergillus flavus, Botrytis cinerea, Alternaria alternata) was studied in this paper. The best antibacterial properties were demonstrated by derivatives 11Ba, trans10Bb and 11Bb, and the most sensitive microorganism was found to be the gram-positive bacterium S. epidermidis. The derivative 11Bb showed the best antifungal activity, while C. albicans was resistant to all tested derivatives, and C. parapsilosis was fully inhibited in the presence of the derivative 11Ba and 11Bb. Among the filamentous fungi, only the dermatophyte M. gypseum was partially inhibited. Biofilms represent the most prevalent type of microbial growth in nature and are crucial to the development of clinical infections. Newly synthesized derivatives were also added into the medium throughout the biofilm formation. We have observed a significant decrease of biofilm formation in the presence of quinolizidine derivatives, testifying to their significant antimicrobial activity. It seems that the relationship between antimicrobial activity and the structure is based on the alkaline character due to nitrogen, the saturated basic quinolizidine skeleton, and the position of sulfur in the molecule.

(5S,11aS)-5-Hydro­per­oxy-1,5,11,11a-tetra­hydro­[1]benzothieno[3,2-f]indol­izin-3(2H)-one

The absolute configuration of the title compound, C14H13NO3S, was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine moiety adopts an envelope conformation, with the greatest deviation from the mean plane of the ring being 0.661 (2) Å for the bridgehead C atom. The benzothiene ring attached to the indolizine ring system is planar to within 0.008 (2) Å. In the crystal, molecules form chains parallel to the b axis via O—H⋯O hydrogen bonds.

(6S,7S,8S,8aS)-6-Ethyl-7,8-dihy-droxy-1,5,6,7,8,8a-hexa-hydro-indolizin-3(2H)-one monohydrate.

The absolute configuration of the title compound, C10H17NO3·H2O, was assigned from the synthesis. In the molecular structure, the central six-membered ring of the indolizine moiety adopts a chair conformation, with two atoms displaced by −0.578 (2) and 0.651 (1) Å from the plane of the other four atoms [maximum deviation 0.019 (2) Å] The conformation of the fused oxopyrrolidine ring is close to that of a flat envelope, with the flap atom displaced by 0.294 (1) Å from the plane through the remaining four atoms. In the crystal, one of the hydroxy groups is hydrogen-bonded to two water molecules, while the other hydroxy group exhibits an intermolecular hydrogen bond to the carbonyl O atom, resulting in a chain parallel to the b axis.

Crystal, molecular and electronic structure of (3aS,4S,9aS,9bR)-4-ethyl-2,2-dimethylhexahydro-[1,3]dioxolo[4,5-g] indolizin-7(3aH)-one

Abstract Molecules of the title compound, C13H21NO3, crystallize as single enantiomers with four stereogenic centres, their absolute configuration were confirmed by anomalous dispersion effects determined by diffraction measurements on the crystals. Conformations of the pyrrolidine and 1,3-oxolane rings are close to that of an envelope, with the flap atoms displaced by −0.205 (1) and −0.449 (1) Å, respectively, from the plane of the other remaining four atoms. The central six-membered ring of the indolizine moiety adopts a nearly perfect boat conformation, with two atoms displaced by 0.575 (1) and 0.603 (1) Å from the plane of the other remaining four atoms. Crystal structure of the title compound is stabilized by C−H···O hydrogen interactions.

Electronic structure, novel synthesis, and O-H...O and C-H...O interactions in two 6-oxopiperidine-2-carboxylic acid derivatives.

Molecules of (S)-6-oxo-1-(thiophen-2-ylmethyl)piperidine-2-carboxylic acid, C11H13NO3S, crystallize as single enantiomers in the space group P21 and the thiophene ring is disordered over two positions, while (S)-6-oxo-1-(thiophen-3-ylmethyl)piperidine-2-carboxylic acid, C11H13NO3S, crystallizes as a single enantiomer in the space group P212121. Their absolute configurations were confirmed by anomalous dispersion effects in diffraction measurements on the crystals. The molecules of each compound are linked by a combination of strong O-H...O hydrogen bonds and weak C-H...O interactions, resulting in two- and three-dimensional networks, respectively, in the crystal structures.

Crystal, molecular and electronic structure of (5S,8aS)-5-methyl-4,6,7,8,8a,9-hexahydrothieno-[ 3,2-f] indolizinium iodide

Abstract The molecules of the title compound, C11H16NS·I, crystallize as single enantiomer with two stereogenic centre, their absolute configuration were confirmed by anomalous dispersion effects in diffraction measurements on the crystals. The conformation of the pyrrolidine ring is close to that of an envelope, with the flap atom N1 displaced by 0.661 (2) A from the plane of the oder remaining four atoms. The central six-membered ring of the indolizine moiety adopt a half-chair conformation with atom C5 displaced by -0.686 (2) Å from the plane of the oder remaining five atoms. The crystal structure of the title compound is stabilized by C-H···I···H-C hydrogen interactions.