Highly diastereoselective approach to novel tetrahydrofuran-fused indolizidinols: a one-step formation of three contiguous stereocenters

Smart and concise entry to chiral spiro[cyclopentane-indolizidine]-tetraol diastereomers as a new aza-spirocyclic framework

Synthesis of chiral oxacarba-spiroindolizidine tetraols was achieved by alkene cis-dihydroxylation, diol protection, and lactam carbonyl reduction followed ultimately by acetonide deprotection.

Synthesis and sequential diastereoselective incorporation of hydroxyl groups into hexahydrofuro[3,2-f]indolizin-7(2H)-one to give mono-, di- and tetra-hydroxyfuroindolizidines

Dihydrofuro[2,3-f]indolizidinone obtained from biosourced reagents even at multigram-scale was used as an advanced building-block with up to five points of chemical diversification. This resulted in the sequential synthesis of a series of mono-, di- and tetra-hydroxyfuranoindolizidines belonging to a very scarce and elaborate tetrahydrofuran-fused indolizidine family with up to six controlled stereogenic centers. These sequences include, among others, diastereoselective olefin epoxidation, stereoselective epoxide ring opening into tetrahydrofuran trans-diols, their protection as an ester or acetonide, and lactam carbonyl reduction ultimately followed by acetate or acetonide deprotection.

(±)-Homocrepidine A, a Pair of Anti-inflammatory Enantiomeric Octahydroindolizine Alkaloid Dimers from Dendrobium crepidatum

A pair of racemic indolizidine enantiomers, (±)-homocrepidine A (1), and a piperidine derivative, homocrepidine B (2), were isolated from Dendrobium crepidatum along with the known alkaloid crepidine (3). The racemic mixture of 1 was separated into a pair of enantiomers, (+)-1 and (-)-1, by HPLC using a chiral chromatographic substrate, which represents the first successful example of resolving indolizidine racemic mixtures. The absolute configurations of (+)-1 and (-)-1 were assigned from single-crystal X-ray diffraction data. The evaluation of anti-inflammatory activity with LPS-induced RAW 264.7 macrophages revealed that (+)-1 strongly inhibited the production of nitric oxide (IC50, 3.6 μM) and significantly decreased the expression of inducible nitric oxide synthase, while (-)-1 and (±)-1 only had moderate inhibitory effects (IC50, 22.8 and 14.7 μM). Compound 2 showed moderate anti-inflammatory activity (IC50, 27.6 μM).

Substrate induced diastereoselective hydrogenation/reduction of arenes and heteroarenes

Nature/structure of the (hetero)arene, substituent and reducing agent affect the diastereoselectivity.

(3aR,8aS,9S,9aR)-9-Hydroxy-perhydro-furo[3,2-f]indolizin-6-one

In the title compound, C(10)H(15)NO(3), the central six-membered ring of the indolizine system adopts a chair conformation, while the oxopyrrolidine and hydro-furan rings attached to the indolizine ring system have envelope conformations. In the crystal, the mol-ecules form chains parallel to the b axis via inter-molecular O-H⋯O hydrogen bonds. The absolute configuration was assigned from the synthesis.

(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.