Synthesis of spiro[1,4‐benzothiazine‐2,2′‐pyrans] starting from methyl β‐D‐arabino‐2‐hexulopyranosonate

Abstract

Dedicated to Professor Klaus Burger on the occasion of his 60th birthday Methyl β‐D‐arabono‐2‐hexulopyranosonate 1 has via the novel glycosyl donor 3 been transformed into the thiophenyl glycosides 4 and 5. Catalytic hydrogenation of the nitro compound 4 in alkaline solution led to spontaneous cyclization and deprotection to form the cyclic hydroxamic acid 7. The related lactams 8 and 9 were obtained from amine 5. The spiro[1,4‐benzothiazine‐2,2′‐pyrans] 7–9 are the first representatives of a novel class of heterocycles structurally related to bioactive natural products. As shown by the values for J3′,4′ and J4′,5′ the glycosides 4, 5 and 6 adopt a 5C2 conformation of the pyranoid ring whereas the 1,4‐benzothiazine system in 7–9 forces a conformational change into the 2C5 conformation.

Glucopyranosylidene-spiro-benzo[b][1,4]oxazinones and -benzo[b][1,4]thiazinones: Synthesis and Investigation of Their Effects on Glycogen Phosphorylase and Plant Growth Inhibition

“…Anomeric spiroketals of pyranoid sugar derivatives in which additional heteroatoms, especially nitrogen, can be found in a six-membered ring are scarcely known. Syntheses of glycopyranosylidene spiro derivatives of 1,2-oxazines, 1,3-oxazinones, 1,4-oxazines, 1,4-oxazinones, − and 1,4-thiazinones have been reported; however, their biological activity is practically unexplored so far. Only weak glycosidase inhibition and cytotoxicity for some 1,3-oxazinone derivatives have been reported …”