Efficient Photoinduced Deoxygenation Vicinal to carbonyl Groups in Sugar Derivatives

C. MARINO; A. BORDONI; R. M. DE LEDERKREMER

Whistler, BC, Canada

Simposio; XXIII International Carbohydrate Symposium; 2006

International Carbohydrate Organization

            The development of specific deoxygenation methods is important for the preparation of many biological important sugars from readily available precursors. Among a variety of methods for carbohydrate deoxygenation, tin radical cleavage of thiono esters developed by Barton and McCombie has been widely used [1]. However, avoiding the use of reagents such as tri-n-butyltin hydride and thiocarbonyl reagents is desirable from the environmental and economic point of view.             In connection with our project on the development of synthetic tools for studies related to galactofuranose glycobiology, we have synthesized deoxygenated ¥â-D-galactofuranosides in order to establish the importance of each hydroxyl group in the interaction with ¥â-D-galactofuranosidase [2-4]. For the synthesis of 2-deoxy-D-lyxo-hexofuranosides (2-deoxy-galactofuranosides), we started from D-galactono-1,4-lactone, and the deoxygenation step was performed via a photoinduced electron transfer (PET) reaction on compound 1, using 9-methylcarbazole (MCZ) as photosensitizer [4]. Interestingly, the reaction conditions necessary for the deoxygenation of compound 1 were extremely mild in comparison with those required for not carbonyl compounds. The effectiveness of this reaction on lactone derivatives, should be due to the stabilization by the carbonyl group of the intermediate radical. With the purpose of establishing an efficient protocol for the deoxygenation of aldonolactones at C-2, we prepared different derivatives of D-galactono- and D-glucono-1,4-lactones and we optimized the conditions for the PET reaction, which led to the free deoxygenated aldonolactones, and deoxygenated derivatives useful as intermediates for the synthesis of disaccharides having the reducing unit deoxygenated at C-2.             The study was extended to PET deoxygenation at C-5 of the glucuronic acid derivative 2. Deoxygenation was confirmed by the appearance of C-5 35.8 ppm in the 13C-NMR spectrum. The product of deacylation of compound 2 was also isolated from the reaction mixture.