Diethylzinc-mediated one-step stereoselective synthesis of alpha-fluoroacrylates from aldehydes and ketones. Two different pathways depending on the carbonyl partner.

A efficient methodology allowing the one-pot stereoselective synthesis of alpha-fluoroacrylates, based on the addition of ethyl dibromofluoroacetate to a carbonyl derivative using diethylzinc as organometallic mediator, is described. Two different pathways have been identified depending on the involved carbonyl partner. In the case of aldehydes, an E2-type mechanism has been identified, whereas ketones go through an E1cb-type mechanism.

Diastereoselective alkylation of 2,3,4,6-Di-O-isopropylidene-2-keto-L-gulonic amides. Application to the asymmetric synthesis of 1-substituted-1,2,3,4-tetrahydroisoquinolines and 1-substituted-1,2,3,4,-tetrahydro-beta-carbolines.

The diastereoselective alkylation of amides 3a,b and 7a,b derived from gulonic acid is described. Substituted compounds are obtained in good yield and high diastereoselectivity. A mechanistic investigation establishes that the diastereoselectivity did not arise from an initial asymmetric deprotonation. The stereochemistry is then determined during the alkylation step.

Synthesis of alpha-substituted beta-amidophosphines by diastereoselective alkylation. A new access to chiral ligands for asymmetric catalysis.

Chiral beta-amidophosphine boranes 7a-f can be diastereoselectively alkylated, using O-protected amino-alcohols as chiral inducers, to furnish alpha-substituted beta-amidophosphine boranes 8a-f and 9-12 with up to 72% diastereoisomeric excess. Selective deprotection afforded optically pure carboxylic derivative 13 which is a key intermediate for the synthesis of various potential chiral ligands for asymmetric catalysis.

Brachycerine, a novel monoterpene indole alkaloid from Psychotria brachyceras.

Brachycerine (1), an unusual alkaloid from the leaves of Psychotria brachyceras, was characterized through spectroscopic data interpretation and its stereochemistry established by NOE difference techniques. Brachycerine (1) was found to be restricted to shoots in rooted cuttings of P. brachyceras (0.018 +/- 0.004% dry weight), and accumulation was unaffected by root induction treatment with auxin.

Synthesis and conformational analysis of two 2-oxopiperazine-containing tetrapeptide analogues.

One unsubstituted and one stereoselectively prepared 3-(S)-substituted-2-oxopiperazine have been used as dipeptide templates to generate tetrapeptide analogues. NMR analysis shows that these tetrapeptide analogues present an inverse gamma-turn conformation in chloroform.

Naturally occurring somatostatin and vasoactive intestinal peptide inhibitors. Isolation of alkaloids from two marine sponges.

The vasoactive intestinal peptide (VIP) and somatostatin (somatotropin release inhibiting factor, SRIF) are important neurotransmitters in a number of basic physiological events. Their disturbances have been reported in many diseases such as cystic fibrosis, impotent man (VIP), Alzheimer's disease, and some tumours (SRIF). Xestospongine B (1), sceptrine (2), and ageliferine (3), three alkaloids isolated from Xestospongia sp. and Agelas novaecaledoniae are reported as somatostatin and VIP inhibitors. The natural products 1, 2 and 3 exhibited a high affinity for somatostatin (IC50 = 12 microM, 0.27 microM, and 2.2 microM, respectively), 2 and 3 showed an affinity for VIP (19.8 microM and 19.2 microM, respectively). Due to the interaction between non-peptidic compounds and somatostatin/VIP receptors, these three alkaloids could be promising agents in the research on natural non-peptidic compounds for therapeutical interventions.

Indole alkaloids from Antirhea lucida.

A new indole alkaloid, N,N-methyl-3'-indolylmethyl-5-methoxytryptamine, as well as the known gramine, N,N-dimethyltryptamine and 6-methoxy-2-methyl-1,2,3,4-tetrahydro-beta-carboline were isolated from the roots of Antirhea lucida (Sw.) Hook (Rubiaceae). Their structures were established by spectroscopic methods.

Alfalfa Root Flavonoid Production Is Nitrogen Regulated.

Flavonoids produced by legume roots are signal molecules acting both as chemoattractants and nod gene inducers for the symbiotic Rhizobium partner. Combined nitrogen inhibits the establishment of the symbiosis. To know whether nitrogen nutrition could act at the level of signal production, we have studied the expression of flavonoid biosynthetic genes as well as the production of flavonoids in the roots of plants grown under nitrogen-limiting or nonlimiting conditions. We show here that growth of the plant under nitrogen-limiting conditions results in the enhancement of expression of the flavonoid biosynthesis genes chalcone synthase and isoflavone reductase and in an increase of root flavonoid and isoflavonoid production as well as in the Rhizobium meliloti nod gene-inducing activity of the root extract. These results indicate that in alfalfa (Medicago sativa L.) roots, the production of flavonoids can be influenced by the nitrogen nutrition of the plant.

A preliminary chemotaxonomic review of Kopsia (Apocynaceae).

The present paper is the result of a botanical and chemical study of the Indo-Pacific genus Kopsia (Plumerioideae-Rauvolfieae) Apocynaceae. Some of the species of this genus possess medicinal uses. A survey of the accepted taxa and their synonymy, based on the study of types, is presented. Studies on alkaloids provides chemotaxonomic information. Indeed, in some cases, chemical relationships occur between species belonging to the same botanical group.

Two new alkaloids from Xestospongia sp., a New Caledonian sponge.

Five alkaloids have been isolated from a New Caledonian sponge Xestospongia sp. These include three known xestospongin derivatives, the new demethylxestospongin B (1) and a tetrahydrocarboline derivative 5. The structures of the new compounds 1 and 5 have been established by nmr studies and comparison with previously described products.

New Polyindolenine Alkaloids from Calycodendron milnei.

Four new alkaloids, representing the first members of new groups of polyindolinic alkaloids, have been isolated from the aerial parts of CALYCODENDRON MILNEI along with other alkaloids. The names vatine, its stereoisomer vatine A, vatamine, and vatamidine are proposed. They are polymers of six, seven, and eight N(b)-methyltryptamine units, respectively.