Synthesis of 5-deoxy-beta-D-Galactofuranosides (5-deoxy--l-arabino-Hexofuranosides) starting from D-Galacturonic acid by Photoinduced Electron Transfer (PET) Deoxygenation

MARINO C.; BORDONI, A.; LO FIEGO, M. J.; MUCHNIK DE LEDERKREMER, R.

Carbohydrate Chemistry: Proven Synthetic Methods 3

CRC Press Taylos and Francis groupr

Año: 2015; p. 45 - 55

Developing specific deoxygenation methods for carbohydrates is important as deoxy sugars are useful not only for enzymatic characterization, but also for the synthesis of natural products from carbohydrate precursors as chiral templates.1-3 Since its development in 1975, the Barton-McCombie deoxygenation method has been extensively employed.4 However, this procedure involves the use of organotin compounds, which are toxic, expensive, and difficult to remove. Thus, many modifications have been later developed using other hydride donors.5Photochemical reactions are attractive in the modern context of green chemistry. In the frame of our project dedicated to the characterization of -D-galactofuranosidases6 we found very useful the photoinduced electron-transfer (PET) reduction7 of 3-(trifluormethyl)benzoyl esters, using 9-methylcarbazole (MCZ) as photosensitizer. This reaction was first used by Rizzo et al. for the synthesis of deoxyribonuleosides (A, Scheme 2). We investigated the PET deoxygenation on D-galactono-1,4-lactone (B),8,9 D-galacturonic acid (C) and D-glucofuranosidurono-6,3-lactone (D) derivatives.10 The reaction is particularly efficient for reduction of the HO vicinal to the carbonyl group of lactones or esters (Scheme 2), allowing to significantly reduce the irradiation time and the MCZ amount. The effectiveness of the reaction relies on the stabilization by the carbonyl group of the intermediate radical I, formed by homolytic cleavage of the hydroxyl group conveniently derivatized (Scheme 3).