Synthesis of the Purported Structure of Glyphaeaside C and Proposed Revisions to the Structures of the Glyphaeaside Alkaloids

The 10 glyphaeaside alkaloids isolated from the roots of Glyphaea brevis were originally purported as piperidine-based 1-C-alkylated iminosugars, with the A-, B-, and C-type glyphaeasides bearing l-DFJ, DGJ, and DNJ ring configurations, respectively. Subsequent investigations have revealed glyphaeaside C as being a pyrrolidine-based iminosugar with a DMDP ring configuration via total synthesis of the revised structure. In this work, side chain diastereomers of the originally purported structure of glyphaeaside C (10) and two related α-1-C-alkylated DNJ derivatives were synthesized from a common precursor, which was prepared in turn via stereoselective Grignard addition to a protected d-glycosylamine, followed by a reductive amination-cyclization sequence. Glycosidase inhibitory activity studies revealed general structure 10 as having potent inhibition against various α-glucosidases and weak inhibition against almond β-glucosidase in agreement with similar DNJ-based iminosugars and in contrast to natural glyphaeaside C, suggesting that the (1,2-dihydroxy-3-phenyl)propyl moiety does not play a particularly vital role in the inhibitory modes of action of either compound. Furthermore, the absolute configuration of natural glyphaeaside C was proposed as that of d-DMDP, and the structures of the A- and B-type glyphaeasides were revised as 1-deoxy-DALDP and DALDP derivatives, respectively, based on interpretation of their reported NMR spectroscopic data.

Cyanomethyl (CNMe) ether: an orthogonal protecting group for saccharides

Logical manipulation of protecting groups is one of the vital strategies involved in the synthesis of complex oligosachharides. As opposed to the robust permanent protecting groups, the chemoselective protection-deprotection processes on orthogonal protecting groups have facilitated the synthesis of the target molecules with higher effeciency. While the derivatives of benzyl ethers are the most popular orthogonal ether based protecting groups for hydroxyls, the exploration of methyl ethers for similar synthetic application is much limited. We herein report cyanomethyl (CNMe) ether as a readily synthesized orthogonal protecting group for saccharides. The ether moiety was rapidly removed under Na-naphthalenide conditions in good to excellent yields and was found to be compatible with other well-known benzyl/methyl/silyl ether and acetal protecting groups. Additionally, the CNMe group was observed to be tolerant to standard reagents used for the deprotection of ether, ester and acetal protecting groups. The protection and deprotection steps remained unaffected by the position of hydroxyl, the configuration of monosaccharides or the presence of olefins in the skeleton.

Dichotomous Selectivity in Indium-Mediated Aza-Barbier-Type Allylation of 2-N-Acetyl Glycosyl Sulfinylimines in Brine: Convenient Access to Potent Anti-Influenza Agents

A highly diastereoselective indium-mediated allylation of 2-N-acetyl glycosyl sulfinylimines in brine under mild reaction conditions is reported. The method allows the achievement of a highly remarkable dichotomous selectivity for substrates, providing a single diastereoisomer of the product in 80-98% yield. With chiral (S)-homoallylic sulfinamide (R_S)-5 and (R_S)-8 formed as key intermediates, two potent anti-influenza agents, zanamivir and zanaphosphor, were synthesized in 50% and 41% overall yields, respectively.

Metal-free synthesis of imino-disaccharides and calix-iminosugars by photoinduced radical thiol–ene coupling (TEC)

Deprotected iminosugar alkenes were subjected to thiol–ene coupling with deprotected sugar thiols to afford new imino-disaccharides. Two thiol–ene couplings converted these alkenes into iminosugar thiols and then multivalent iminosugars.

Glycoside Mimics from Glycosylamines: Recent Progress

Glycosylamines are valuable sugar derivatives that have attracted much attention as synthetic intermediates en route to iminosugar-C-glycosyl compounds. Iminosugars are among the most important glycomimetics reported to date due to their powerful activities as inhibitors of a wide variety of glycosidases and glycosyltransferases, as well as for their use as pharmacological chaperones. As they provide ready access to these important glycoside mimics, we have reviewed the most significant glycosylamine-based methodologies developed to date, with a special emphasis on the literature reported after 2006. The groups of substrates covered include N-alkyl- and N-benzyl-glycosylamines, N-glycosylhydroxylamines, N-(alkoxycarbonyl)-, and N-tert-butanesulfinyl-glycosylamines.

Pyrrolizidine alkaloids: occurrence, biology, and chemical synthesis

Covering: 2013 up to the end of 2015This review covers the isolation and structure of new pyrrolizidines; pyrrolizidine biosynthesis; biological activity, including the occurrence of pyrrolizidines as toxic components or contaminants in foods and beverages; and formal and total syntheses of naturally-occurring pyrrolizidine alkaloids and closely related non-natural analogues.