A reliable, facile, high overall yielding and diastereoselective synthesis of ketoheptoses was developed and applied for preparation of the two most diabetogenic ketoheptoses as well as in a modified version for the synthesis of kamusol.
Bei Umsetzungen einfacher Modellverbindungen rnit lodtrimethylsilan zeigen sich hohere Reaktionsraten bei Acetaten und bei Cyclohexylestern. Bei Einsatz primarer und sekundarer Saccharid-Acetoxyderivate wird dagegen die ausschlieRliche Bildung der Glycosyliodide festgestellt. Pentaacetylhexopyranosen reagieren mit Iodtrimethylsilan in hohen Ausbeuten zu den entsprechenden Tetraacetylglycosyliodiden. Auch Methylglycoside lassen sich umsetzen; beim Lactoseoctaacetat zeigt sich, daR unter a-Heptaacetyllactosyliodid-Bildung die interglycosidische Bindung intakt bleibt. Besonders wertvoll ist das Verfahren zur Gewinnung der 2 Desoxyglycosyliodide. Entsprechende Umsetzungen rnit Bromtrimethylsilan werden erfolgreich vorgenommen. Epoxidoffnungen mit lodtrimethylsilan verlaufen bei sterischer Fixierung des Saccharid-Oxirans zu den fruns-diaxialen bzw. bei sterisch beweglichen Derivaten uberwiegend zu den trans-diaquatorialen lodhydrinen.
Synthetic Application of Iodo-and Bromotrimethylsilane in Saccharide ChemistryIn simple model compounds an enhanced rate is observed in the reaction of iodotrimethylsilane with acetates and with cyclohexyl esters. Primary and secondary acetoxy-substituted saccharides show an exclusive formation of glycosyl iodides. Accordingly, pentaacetyl hexopyranoses and iodotrimethylsilane give in high yields the corresponding glycosyl iodides. Methyl glycosides can be transformed similarly, and with lactose octaacetate the formation of a-heptaacetyllactosyl iodide proceeds smoothly without rupture of the interglycosidic linkage. This procedure is particularly valuable for the synthesis of 2-deoxyglycosyl iodides. Corresponding reactions with bromotrimethylsilane are achieved in a similar way. By opening of epoxides with iodotrimethylsilane in the case of sterically fixed saccharide oxiranes the fruns-diaxial, and with more flexible derivatives predominantly the rruns-diequatorial iodohydrines are obtained.In jiingster Zeit sind eine Reihe von Untersuchungen iiber die vorteilhafte synthetische Anwendung von Iod-und Bromtrimethylsilan beschrieben worden, unter denen die Esterspaltung' -4) R-C0,R' + Me,SiX -.+ R-CO,SiMe, + R'X und die Reaktion rnit offenkettigen Acetalen 5, R,C(OR'), + Me,SiX --t R,CO + R'OSiMe, + R'X unser Interesse beanspruchen.Be& der zur Esterspaltung entwickelten Methode wird mit Iodtrimethylsilan die Umesterung zum Carbonsaure-trimethylsilylester bewirkt, dessen Aufarbeitung eine milde 0 Verlag Chemie, GmbH, D
The straightforward syntheses of six regioisomeric mono‐ and difluorinated D‐manno‐heptulose and Kamusol analogues, which use electrophilic or nucleophilic fluorinaton, are reported. D‐manno‐Heptulose shows attractive pharmacological properties in vivo, such as antitumour activity, as well as binding to and accumulating in pancreatic beta cells to induce hyperglycemia. The synthesised analogues represent promising probes for the detection and quantification of beta cells in vivo by 19F MRI techniques, which could help to investigate disease progression. In addition, they are potential candidates for the inhibition of tumour growth.
For the first time, fully fledged phthalocyanines (Pcs) were ex post glycoconjugated, that is, via 1,3-dipolar cycloaddition reaction. This divergent approach gains rapid access to a broad range of highly diverse Pcs bearing chemically sensitive substituents. This will be a breakthrough in generating structure-activity relationships (SAR) for the development of novel bioactive molecules.
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