RESUMO
From sugar to cycloadduct: The effect of the trans-acetonide blocking group and the stereochemistry of the substituents on the regio- and stereoselectivity in the intramolecular nitrone-alkene cycloaddition (INAC) reaction of hept-6-enoses (see scheme) is reported and studied by using theoretical analysis.The positional effect of the trans-acetonide blocking group and the effect of the stereochemistry of the substituents on the regio- and stereoselectivity in intramolecular nitrone-alkene cycloaddition (INAC) reactions of hept-6-enoses are reported. Hept-6-enoses with a 2,3-trans-acetonide group were reacted with N-alkyl hydroxylamine to give a mixture of exo and endo cycloadducts (cyclohexanols and cycloheptanols, respectively). Complete formation of endo cycloadducts (cycloheptanols) was realized for the INAC reaction of hept-6-enoses containing a 3,4-trans-O-isopropylidene ring. Similarly, reaction of a hept-6-enose possessing a 4,5-trans-acetonide group surprisingly afforded exo cycloadducts (cyclohexanols) exclusively. The regio- and stereochemical outcomes of these reactions were rationalized on the basis of transition-state energies obtained by computation.
RESUMO
A pseudo-1,4'- N-linked disaccharide, pseudoacarviosin 5, was constructed via a key palladium-catalyzed coupling reaction of pseudoglycosyl chloride 8 (prepared from d-glucose via a novel direct intramolecular aldol addition in 12 steps) and pseudo-4-amino-4,6-dideoxy-alpha- d-glucose 9 (prepared from l-arabinose via an unusual trans-fused isoxazolidine-selective intramolecular nitrone-alkene cycloaddition in 11 steps). Pseudoacarviosin 5 has been shown to be a potent inhibitor of alpha-glucosidases, particularly the intestinal mucosal enzymes sucrase and glucoamylase of relevance to blood glucose control.
Assuntos
Dissacarídeos/síntese química , Inibidores de Glicosídeo Hidrolases , Hipoglicemiantes/síntese química , Catálise , Diabetes Mellitus/tratamento farmacológico , Dissacarídeos/química , Dissacarídeos/farmacologia , Hipoglicemiantes/química , Hipoglicemiantes/farmacologia , Estrutura Molecular , EstereoisomerismoRESUMO
High-yielding endo-selective intramolecular nitrone-alkene cycloaddition (INAC) reactions of hept-6-enoses controlled by a trans-acetonide to give bridged bicyclo[4.2.1]isoxazolidines exclusively are realized for the first time. The cycloadducts were readily transformed into calystegine, tropane, and hydroxylated aminocycloheptane frameworks. [reaction: see text].
RESUMO
[reaction: see text] Intramolecular nitrile oxide-alkene cycloaddition (INOC) of sugar derivatives with one to four free hydroxyl group(s) is reported. The INOC reaction, using chloramine-T, in the presence of silica gel, to generate nitrile oxides from oximes, proceeded smoothly to afford five- or six-membered carbocycles in good to excellent yields. This new methodology alleviates protection/deprotection steps and makes the synthetic route shorter and more efficient.