Claude Riche

Identification of des-A-triterpenoid hydrocarbons occurring in surface sediments

Abstract Molecular structures of eight tetracyclic hydrocarbons occurring in sediments were established either by synthesis of the corresponding reference compounds or spectroscopic studies (MS, NMR, X-ray diffraction) of the natural products isolated from a pond mud. These products are derived from higher plant 3-oxygenated pentacyclic triterpenes (lupane, oleanane and ursane series) by microbially mediated loss of ring A and subsequent aromatisations.

New nitrogenous and aromatic derivatives from Aglaia argentea and A. forbesii

Seeds and leaves of Aglaia argentea and bark of A. forbesii were extracted. The known cyclopentatetrahydrobenzofuran derivative rocaglaol (1) and the aminopyrrolidine odorine (5), were isolated together with nine new compounds: didesmethylrocaglamide (6), aglains A (7), B (8) and C (9), aglaforbesins A (10) and B (11), ethylrocaglaol (12) and forbaglins A (13) and B (14). Compounds 7–11 and 13,14 possess a new cyclopentatetrahydrobenzopyran and benzoxepine skeleton, respectively, linked to an odorine type moiety. All the structures were elucidated notably by 2D NMR spectroscopy. In addition, the structure of forbaglin A was established by X-Ray crystallographic analysis. Didesmethylrocaglamide revealed strong cytotoxic activity against KB cells (IC50 0.006 μg/ml).

Oxydation et addition des dihalocarbènes sur le β-himachalène

Resume Reaction of β-himachalene with one equivalent of dihalocarbene, KMnO 4 or m -CPBA gives regio- and stereospecifically one product resulting from the attack of the C6 C7 double bond. The molecular structure shows that this attack occurs on the α face of this double bond.

Enantioselective synthesis of cyclopropane α-amino acids: Synthesis of N-Boc-cis-(2S,3R,4S)-3,4-methanoproline and N-Boc-(2S,3R,4S)-3,4-methanoglutamic acid

Abstract The title compounds were synthesized by a 5-step facile transformation of the key intermediate 4, itself obtained by a “one-pot” sulfone-mediated cyclopropanation from chiral synthon (R)-1 and (2 R )-glycidyl triflate.

The asymmetric michael addition process involving chiral imines : stereochemical data in support of a cyclic-like transition state

Abstract Additions of imine 4 to Michael acceptors 5 and 8 are both highly selective processes. The observed stereocontrol of the newly created asymmetric centers in the resulting adducts strongly supports cyclic-like transition states.

Asymmetric synthesis. XXXI: Synthesis of 2-substituted piperazines from chiral non-racemic lactams

Abstract A series of 3-substituted piperidines in enantiomerically pure form has been synthetized from lactam 3 by a stereospecific route involving a postulated rigid amide enolate. This strategy has been applied to the synthesis of (+)-stenusine 10.

A Formal Synthesis of (+)-Huperzine A

Abstract A new formal stereoselective synthesis of (+)-Huperzine A (1) was achieved using as a key step a palladium mediated annulation between 2-methylene-1,3-propanediol diacetate and (1R,2S)-2-phenylcyclohexanol derived β-ketoester 2c.

1,3-Dipolar cycloadditions of nitrones to α,β-unsaturated γ-lactams derived from (S)-pyroglutaminol☆

Abstract α,β-Unsaturated γ-lactams undergo regio- and stereoselective 1,3-dipolar cycloadditions with N-benzyl and N-methyl nitrones and can act as acceptors in conjugate addition of N-methylhydroxylamine. These reactions give access to highly functionalized pyrrolidones.

Composés bromés de Rytiphlea tinctoria (Rhodophyceae)

Abstract Four aromatic bromo compounds have been isolated from the ethanolic extract of Rytiphlea tinctoria after treatment with diazomethane: 2,4-dibromo-1,3,5-trimethoxy-benzene,5,6,3′,5′-tetrabromo-3,4,2′,4′,6′-pentamethoxydiphenylmethane, 5,6-dibromo-3,4-dimethoxy-benzyl alcohol and its ethyl ether. In addition to sterols, amino acids, this extract also contains quinonoid bromo-pigments which could play a role in photosensitisation of chlorophylls, a role normally taken by the phycobilins, in other Rhodophyceae.

Racemization processes at a quaternary carbon center in the context of the asymmetric Michael reaction

Abstract Several examples of racemization process at a quaternary carbon center affecting Michael adducts were reported. A brief statement to prevent the occurrence of the interfering retro-Michael reaction was also presented.