Selective hydroxy group protection of gallic acid

An efficient procedure allowing selective differentiation of the 4-hydroxy group of Me gallate was reported. Me gallate was triacetylated to give 3,4,5-tris(acetyloxy)benzoic acid Me ester which was then regioselectively deacetylated to give the 3,5-tris(acetyloxy)-4-alkoxybenzoic acid Me esters I (R = alkyl, allyl, benzyl). [on SciFinder (R)

A highly stereoselective synthesis of (2S, 3S)-beta -hydroxyleucine

An efficient asym. synthesis of (2S,3S)-beta -hydroxyleucine is described. The key step in the synthesis was a highly diastereoselective nucleophilic addn. of Grignard reagent to N,N-dibenzyl-O-TBS-serinal (TBS = SiMe2CMe3). This strategy should be applicable to the synthesis of other related beta -hydroxy amino acids. [on SciFinder (R)

Diastereoselective Synthesis of gamma -Hydroxy-beta -Amino Alcohols and (2S,3S)-beta -Hydroxyleucine from Chiral D-(N,N-Dibenzylamino)serine (TBDMS) Aldehyde

Title serine deriv. I (TBDMS = tert-butyldimethylsilyl; Bn = benzyl) was synthesized from D-serine in excellent overall yield. The reactions of I with Grignard and organocerium reagents were highly stereoselective (Felkin model) to give gamma -hydroxy-beta -amino alcs. II (R = CHMe2, Me, Ph, Bu) in good yield. Transformation of II (R = CHMe2) into (2S,3S)-beta -hydroxyleucine (III) is also reported. [on SciFinder (R)

A Convergent Approach to Cyclopeptide Alkaloids: Total Synthesis of Sanjoinine G1

A general strategy for the synthesis of cyclopeptide alkaloids contg. an endocyclic aryl-alkyl ether bond has been developed featuring a key intramol. SNAr reaction. The importance of the N-terminal protective group in the realization of such a strategy is documented. From the appropriate amino acid constituents, the natural sanjoinine G1 (I), a 14-membered para-cyclophane, has been synthesized in seven steps with 21% overall yield. [on SciFinder (R)

A novel strategy towards the total synthesis of cyclopeptide alkaloids

Cyclic peptides I (R = benzyl, allyl; R1 = NO2, NH2, H), which contain the macrocyclic aryl ether skeleton of some naturally occurring alkaloids such as pandamine, were prepd. Key to the synthetic strategy was the cyclocondensation of the linear peptides II [NR2 = NHBOC, N(benzyl)2, N(allyl)2; R2 = SiMe2CMe3, H] to form macrocycles I. Thus, II [NR2 = N(allyl)2, R2 = H] in a DMF soln. was treated with Bu4N+F- in the presence of mol. sieves to form I (R = allyl, R1 = NO2), which was subsequently converted first to the amine I (R = allyl, R1 = NH2) and then to the target macrocycle I (R = allyl, R1 = H). [on SciFinder (R)

Procédé de préparation de composés d'intérêt par cyclisation intramoléculaire et formation d'un pont éther biaryl

Novel method for intermolecular cyclization by formation of a biaryl ether bridge through the reaction as shown above. In formulas (I) and (II) R1 is a nitro radical adjacent to the oxygen bridge, Hal is a fluoride or chlorine atom, R2, R3 and R4 together form a peptidic chain, in the presence of a weak phase in a heterogeneous medium. The invention also concerns compounds of formulas (I) and (II) and the use of compounds of formula (I) to obtain useful compounds

A Convergent Synthesis of 14-Membered F-O-G Ring Analogs of the Teicoplanin Binding Pocket via Intramolecular SNAr Reaction

An intramol. SNAr reaction for efficient macrocyclization via biaryl ether formation was developed for syntheses of the 14-membered macrocycles I and II (R = NH2, NO2) related to F-O-G ring of teicoplanin. Chloride as well as fluoride could be used as the leaving group in this reaction. However, the latter was preferred since it required milder conditions. Both ortho and para nitro, fluoro disubstituted arom. rings were suitable for the macrocyclization reaction with tethered aryl oxides. The nonproteinogenic alpha -amino acid III, required for the synthesis of II, was prepd. via an asym. Strecker synthesis using (R)-phenylglycinol as a chiral auxiliary. The overall synthetic strategy was convergent, and the cyclization could be performed in the presence of the highly sensitive arylglycine unit without racemization. [on SciFinder (R)

La sécurité alimentaire à l'heure du néo-libéralism : 3. Les initiatives de substitution

L'histoire de la région du Gooy (Sénégal) depuis le milieu du XIXe siècle a été marquée par des crises alimentaires récurrentes. En mettant en perspective l'évolution des types de crises, des systèmes de régulation et des tendances démographiques, on peut rendre compte du passage des "années de famine" de la période coloniale aux "années difficiles" de la période actuelle, pour reprendre des expressions soninké. Cette évolution s'est accompagnée de la disparition des grandes mortalités dues aux crises ou aux épidémies, puis d'une forte croissance démographique. Si les problèmes alimentaires se posent aujourd'hui en termes moins aigus, c'est au prix d'une nouvelle dépendance par rapport aux revenus migratoires. (Résumé d'auteur

Palladium catalyzed reductive deprotection of alloc: Transprotection and peptide bond formation

N-allyloxycarbonyl group could be efficiently removed using sodium borohydride as hydride donor in the presence of catalytic amount of palladium (0). The conditions were applied to chemoselective protecting group transformation (transprotection) and peptide bond formation

Asymmetric synthesis of 3,5-bis(isopropyloxy)-4-methoxyphenyl glycine by way of a diastereoselective Strecker reaction and an Evans electrophilic amination reaction

Two short syntheses of D-N-Boc-3,5-bis(isopropyloxy)-4-methoxyphenylglycine, a central unit of vancomycin type antibiotics, have been developed. A diastereoselective Strecker amination reaction using (S)-phenylglycinol as a chiral inducer was the key step in the first synthesis, while Evans' electrophilic azidation technol. was employed for introducing both the amino function and the chirality in the second strategy. [on SciFinder (R)