On the Regio- and Stereoselective Synthesis of Aminocyclitols from Cyclitol Epoxides: The Effect of Li as a Chelating Agent

One pot synthesis of thio-glycosides via aziridine opening reactions

thio-Glycosides with a pseudo-disaccharide structure are synthesized via aziridine opening reactions starting from glycosyl thioacetates with a one-pot protocol, which affords glycomimetics equipped for easy and stable conjugation to aglycones.

A computational study of regioselectivity in aluminum hydride ring-opening of cis- and trans-4-t-butyl and 3-methylcyclohexene oxides

Nucleophilic ring opening of cyclohexene oxides is known to proceed preferentially through the trans-diaxial pathway (the Fürst-Plattner rule). This preference, however, is not absolute, and can be affected by substituents on the cyclohexene oxide ring, as illustrated by LiAlH4 ring-opening of the cis- and trans-isomers of 4-t-butyl- and 3-methylcyclohexene oxide (cis- and trans-1, cis- and trans-2). We performed B3LYP/6-31+G*(PCM) geometry optimizations to locate the chair-like and twist-boat-like transition structures for the hydride attacks on the pseudoaxial and pseudoequatorial conformers of these epoxides. Our calculations are consistent with the experimental observation of effective Fürst-Plattner control of AlH4--opening of cis-1, trans-1, and cis-2, but low selectivity in ring-opening of trans-2. Our data at B3LYP/6-31+G*(PCM) suggests this reduction in selectivity is due to a diminished pseudoequatorial preference of the 3-methyl group in trans-2 relative to that in cis-2. The two calculated chair-like transition structures for hydride opening of trans-2 differ in activation energy free energy (ΔΔG‡) by only 0.4 kcal mol-1. Thus, these calculations account for the reduced regioselectivity of ring opening seen for trans-2 by AlH4- and other nucleophiles.

Synthesis and evaluation of hydroxymethylaminocyclitols as glycosidase inhibitors

Four series of C7N aminocyclitol analogues of glucose were synthesized by stereocontrolled epoxide opening of hydroxyl protected forms of the cyclohexane epoxides cyclophellitol and 1,6-epi-cyclophellitol. The resulting hydroxymethyl substituted aminocyclitols were tested as glycosidase inhibitors. Cyclitols having an amino group in an α configuration at a position equivalent to the anomeric in the sugar were found to be low micromolar inhibitors of the α-glucosidase from baker's yeast with Ki's near to 2 μM. On the other hand, N-octyl aminocyclitols having the nitrogen substituents in an α or β configuration were found to be good inhibitors of recombinant β-glucocerebrosidase with Ki values between 8.3 and 17 μM, and also inhibited lysosomal β-glucosidase activity in live cells at low-micromolar concentrations. A computational docking study suggests a differential binding among the different series of β-glucocerebrosidase inhibitors. In agreement with the experimental results, the binding poses obtained indicate that the presence of an alkyl lipid substituent in the inhibitor mimicking one of the lipid chains in the substrate is critical for potency. In contrast, the matching of hydroxymethyl substituents in the aminocyclitols and the parent glucosylceramide does not seem to be strictly necessary for potent inhibition, indicating the risk of simplifying structural analogies in sugar mimetic design.

Regio- and stereoselective synthesis of new diaminocyclopentanols

The optimal conditions for regio- and stereoselective epoxide ring opening of N,N-disubstituted 1,2-epoxy-3-aminocyclopentanes by different nucleophilic reagents have been developed. The substituents on the nitrogen atom in the epoxide precursor and the orientation of the oxirane ring are crucial for the reaction outcome. Thus, treatment of (1RS,2SR,3SR)-1,2-epoxy-3-(N,N-dibenzylamino)cyclopentane (3b) with amines gave a mixture of C1 and C2 regioadducts, while the use of (1RS,2SR,3SR)-1,2-epoxy-3-(N-benzyl-N-methylamino)cyclopentane (3a) led ultimately to C1 adducts. Base-catalyzed aminolysis of epoxides 6a,b afforded mainly C1 adducts 13a,b arising from trans-diaxal opening of the epoxide ring. Using a Lewis acid catalyst, epoxides 6a,b were transformed into diaminocyclopentanols 14a,b via an alternative pathway involving the formation of aziridinium intermediate 17.

Annulation of β-aryl-α-nitro-α,β-enals and 2,2-dimethyl-1,3-dioxan-5-one: a one-step assembly of nitrocyclitols. Application to a short practical synthesis of (±)-7-deoxy-2-epi-pancratistatin tetraacetate

A novel, highly stereocontrolled formal [3 + 3] annulation of beta-aryl-alpha-nitro-alpha,beta-enals with the enamine derived from 2,2-dimethyl-1,3-dioxan-5-one and pyrrolidine afforded protected nitrocyclitols with five newly created stereocentres and constituted the key step in a short, gram-scale synthesis of a pancratistatin analogue.

Regio- and Stereoselective Synthesis of Aminoinositols and 1,2-Diaminoinositols from Conduritol B Epoxide

[Chemical reaction: See text] A systematic approach to the regio- and stereoselective synthesis of aminoinositols and 1,2-diaminoinositols arising from tetra-O-benzylconduritol B epoxide (9) and its aziridine analogue 22, respectively, is described. In all cases, the synthetic methodologies rely on the regio- and stereocontrolled azidolysis of the starting precursors to give the corresponding trans regioadducts. Subsequent functional group manipulation under strict configurational control affords the isomeric cis adducts. Chemoselective functionalization of the diamine moiety in 1,2-diaminoinositol derivatives can be achieved by the proper design of the reaction sequence and choice of reagents. The described protocols allow efficient access to each of the eight possible configurations of the 1,2-diamino and 1,2-amino alcohol moieties from chemical modifications of the epoxide moiety on the common precursor 9.