Regioselective Synthesis of Partially Protected Trehalose Analogues and Assignment of Ring Size in Isopropylidene Acetal Derivatives by 13 C Nmr Spectroscopy

ABSTRACT

The ¹³C NMR spectra of a range of di-O-isopropylidene acetals of α,α-trehalose and its analogues 1, 2, 4-7 have been studied Attention has been focussed on the chemical shifts of the acetal carbon and methyl groups of the acetals. These parameters are characteristic of ring-size (1,3-dioxolane and 1,3-dioxane). Di-n-butylstannylene and cyclic orthoester intermediates 9 and 12 of 2,6-di-O-benzoyl-α-D-galactopyranosyl 2,6-di-O-benzoyl-α-D-galactopyranoside (8) were used to synthesize the partially protected trehalose analogue having chain extension at positions 4,4′ and 3,3′ (10 and 13) respectively. Acetonation of the synthetic trehalose type disaccharide yielded mainly 3,4:3′,4′-di-O-isopropylidene derivative 4. The benzoylation of 4 followed by acid hydrolysis gave 8 in 85% yield, which was the key intermediate for the synthesis of 10 and 13