Q. Khuong-Huu

Synthesis of methyl 4-amino-2,4,6-trideoxy-3-O-methyl-l-arabino-hexopyranosides (methyl α- and β-l-holantosaminide) and of methyl 4-amino-2,4,6-trideoxy-3-O-methyl-α-l-lyxo-hexopyranoside (methyl α-l-3-epiholantosaminide)

Abstract Methyl 4-amino-2,4,6-trideoxy-3- O -methyl-β- l - arabino -hexopyranoside was synthesized in eight steps, in 40% overall yield, from methyl 4,6- O -benzylidene-2-deoxy-α- d - ribo -hexopyranoside. The inversion of configuration at C-5 was achieved through 5,6-unsaturated methyl 2,6-dideoxy-3- O -methyl-α- d - erythro -hex-5-enopyranoside, followed by stereospecific reduction to give methyl β- l -diginoside. Treatment of methyl 2,6-dideoxy-3- O - p -tolylsulfonyl-α- l - arabino -hexopyranoside with sodium methoxide afforded stereoselectively the 3- O -methyl derivative, which was converted into a mixture of methyl α- l -holantosamine and its 4-amino- l - lyxo -epimer. The latter compound was also synthesized stereospecifically via the 4-azido derivative.

New rearranged limonoids from Harrisonia perforata. III.

Three new limonoids, named haperforins C2 (1), F (2), and G (3), were isolated from a sample of Harrisonia perforata leaves collected in Central Vietnam. Their structures were determined by single-crystal X-ray diffraction analyses, and their NMR and mass spectral data are reported.

Synthèses de 3,6-didésoxy-sucres: Synthèses du méthyl-3,6-didésoxy-4-O-méthyl-α-L-arabino-hexopyranoside (méthyl-4-O-méthylascaryloside) et du méthyl-3,6-didésoxy-α-D-arabino-hexopyranoside (méthyl-α-tyveloside)

Abstract Methyl 4- O -methyl-ascaryloside was synthesized from methyl 2,3- O -benzylidene-4- O -methyl-α- L -rhamnopyranoside, and methyl α-tyveloside from methyl 4- O -benzoyl-6-bromo-6-deoxy-α-D-mannopyranoside. Treatment of methyl 2,3:4,6-di- O -benzylidene-α-D-mannopyranoside with N -bromosuccinimide and reduction with lithium aluminum hydride gave methyl α-tyveloside and methyl 4,6-dideoxy-α-D- arabino -hexopyranoside.

Substitutions allyliques : Nouvelle voie d'accès aux amino-2 didésoxy-2,3 hexopyrannoses synthèse d'un derivé de la tobrosamine

Abstract Synthesis of the methyl α-D-glycoside of N,N-diacetyl tobrosamine 16 from methyl α-D-mannoside 3 is described. Selective introduction of an azido function at C-6 cave 4 . Regio- and stereospecific ring opening of benzylidene derivative 7 , after O-methylation, afforded 8 . Elimination of bromine followed by O-debenzoylation on C-2 led to enose 10 . Azidolysis of 10 by means of alkoxyphosphonium salt (triphenylphosphine, diethylazodicar-boxylate and N 3 H) gave 12 with high stereoselectivity. Reduction, acetylation and acid hydrolysis furnished N,N-diacetylbrosamine. Alternative way to 13 , epimeric 2-amino derivative of 14 , is also described.

Thermolyse et catalyse acide d'azido-steroïdes—6. comparaison avec les reactions de photolyse☆

Abstract Elimination of nitrogen concerted with migration of the alkyl group overlapping the p y orbital of the N α atom of the chromophore N α N β N γ is involved during photochemistry and thermolysis of steroidal azides. Acid catalysed decomposition was explained by alkyl migration to nitrogen, in a manner anti to N 2 elimination. Electronic and steric considerations support these different mechanisms.

New limonoids from Harrisonia perforata (Blanco) Merr.

Two minor compounds were isolated from a sample of Harrisonia perforata leaves collected in central Vietnam, namely haperforin B1, C27H32O9, and haperforin D, C27H34O10. Biogenetically, haperforin D and haperforin B1 can be derived from each other by addition or elimination of water.

Alcaloïdes indoliques : Nouvelles approches de synthèse via les hydrates de carbone

Abstract New approach in total synthesis of indole alkaloids was invented using carbohydrates. Stereocontrolled 15α-H and 15β-H derivatives such as 26a,b and 30a,b were obtained using the same sugar 24. A pure 3α-H, 15α-H compound 32a,b was also prepared via an acyliminium intermediate in a Pictet-Spengler condensation with tryptamine.

Carbohydrates in total synthesis of (−)-antirhine

Abstract Amide 5 was obtained by condensation between pyranose 3 and tryptamine 4 ; in few steps, the indoloquinolizidine 13a was prepared with a perfect stereocontrol of the 2β-H configuration ; total synthesis of (−)-antirhine 2 was then achieved from 13a .

A substituted 1-azaadamantane derivative by “one pot” cyclisation of monocyclic monoterpenoids

Abstract Cyclisation of monocyclic amines via iminium intermediates provides a facile synthesis of a substituted 1-azaadamantane derivative.

Total synthesis of maytansinoids. Approach to 4,6-bisdemethylmaytansine and 4-demethylmaytansine

Abstract A convergent strategy was elaborated to synthesize maytansine 1 and maytansinoids modified on the carbon skeleton, especially 4-demethylmaytansine 2, 6-demethylmaytansine 3, 4,6-bisdemethylmaytansine 4. In this paper, the feasibility of the project was verified by the preparation of key intermediates for the synthesis of 4, 6-bisdemethylmaytansine and 6-demethylmaytansine. The C-1-N open chain compound 18 in the 4,6-bisdemethyl series was obtained.