De Novo Synthesis of an l-Lemonose Thioglycoside Donor from d-Threonine.

A short de novo synthesis of an l-lemonose thioglycoside is described starting from d-threonine. The synthesis leverages a Dieckmann condensation and Stork-Danheiser transposition to arrive at a key vinylogous ester intermediate on gram scale. Ensuing 1,2-addition diastereoselectively establishes the C3 tetra-substituted center and subsequent glycal hydration allows for anomeric functionalization to the thioglycoside. 1H and NOESY NMR analyses reveal that the major α-anomer of thioglycoside deviates from the expected 1C4 conformation.

Synthesis of lemonose derivatives: methyl 4-amino-3-O,4-N-carbonyl-2,4,6-trideoxy-3-C-methyl-α-l-lyxo-pyranoside and its phenyl thioglycoside.

Lemonose is a component of the antibiotic lemonomycin and other antibiotics and natural products. Three routes to the synthesis of the title compound, a protected, desmethyl derivative of lemonose, from l-rhamnose or its glycal, were investigated based on electrophilic cyclization, epoxidation-ring opening, and deoxygenation of an intermediate that was used in the synthesis of the amino sugar callipeltose. The deoxygenation route was successful and it provided the title compound, which was then converted to a phenyl thioglycoside.