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Pseudo-sugar is a compound in which a ring-oxygen of a pyranoid sugar is replaced by a methylene group, and there are 32 theoretically possible stereoisomers in the pseudo-sugar family. All the predicted 16 DL-forms have been synthesized, as well as 9 enantiomers. The most accessible starting material for a synthesis of pseudo-sugars is endo-7-oxabicyclo[2.2.l]hept-5-ene-2-carboxylic acid which is obtained by the DielsAlder reaction of furan and acrylic acid. Recently, it has been found that some pseudo-sugars are almost equally sweet as their respective true sugars. INTRODUCTION In the last two decades, several biologically active branched-chain cyclitols and their erivatives have been found in Nature, such as (+)-(l,2,3/4,5)-tetrahydroxy-l-cyclohexanemethanol (1) (ref. 1), validamycin antibiotics (2) (ref. 2), glucosidase-inhibitors: acarbose (ref. 3), trestatins (ref. 4), adiposins (ref. 5) and oligostatins (refs. 6, 7). Since their common component, hydroxymethyl-cyclohexanetetrol or its amino derivative, is structurally closely related to a true sugar, this compound has been designated as a pseudosugar or a pseudo-amino sugar. Thus, the pseudo-sugar is a name of a class of compounds in which a ring-oxygen of a pyranoid sugar is replaced by a methylene group.