Tony K. M. Shing

-)-Quinic acid in organic synthesis. 1. A facile synthesis of 2- crotonyloxymethyl-(4R,5R,6R)-4,5,6-trihydroxycyclohex-2-enone

Abstract The glyoxalase 1 inhibitor COTC (2-crotonyloxymethyl-(4 R ,5 R ,6 R )-4,5,6-trihydroxycyclohex-2-enone ( 1 ) has been synthesised from (-)-quinic acid in thirteen steps; an interesting rearrangement involving a silyl migration upon oxidation of ( l10 ) is also described.

Lack of glycosidase inhibition by, and isolation from xanthocercis zambesiaca (leguminosae) of, 4-O-(β-D-glucopyranosyl)-fagomine [1,2,5-trideoxy-4-O-(β-D-glucopyranosyl)-1,5-imino-D-arabino-hexitol], a novel glucoside of a polyhydroxylated piperidine alkaloid

Abstract A COSY spectrum has been used to determine the position of inter-residue linkage in 4-O-(β-D-glucopyranosyl) fagomine (1) an example of a new class of glycosides of polyhydroxylated piperidine alkaloids isolated from seed of the legume Xanthocercis zambesiaca . (Bak.) Dunn. Unlike a number of polyhydroxylated piperidines, neither the glucoside (1) nor free fagomine [1,2,5-trideoxy-1,5-imino-D- arabino hexitol] (3) showed any inhibitory activity towards glycosidase enzymes from a variety of sources.

Synthesis of (2S,5S)-bishydroxymethyl-(3R,4R)-bishydroxypyrrolidine from D-mannitol

Abstract A short, efficient, and practical synthesis of (2S,5S)-bishydroxymethyl-(3R,4R)-bishydroxypyrrolidine from D-mannitol involving five sequential reactions (benzylidenation, trifluoromethanesulphonation, hydrazinolysis, hydrogenolysis, and deacetalisation) is described.

(-)-Quinic acid in organic synthesis. 2. Facile syntheses of pseudo-β-D-mannopyranose and pseudo-β-D-fructopyranose.

Abstract Pseudo-β- D -mannopyranose (1) and pseudo-β- D -fructopyranose (2) have been obtained from quinic acid in seven and twelve steps respectively.

Enantiospecific synthesis of (+)-altholactone and its three stereoisomers

Abstract (+)-Altholactone 1 and (+)-7-epi-altholactone 3 were constructed from D -gulonolactone whereas their respective enantiomers (−)-altholactone 2 and (−)-7-epi- altholactone 4 were synthesised from D -mannose, involving stereocontrolled reduction of the lactols 21 and 12 as a key step.

Catalytic asymmetric epoxidation of alkenes with arabinose-derived uloses

Abstract Four l -erythro-2-uloses were readily prepared from l -arabinose via a reaction sequence involving Fischer glycosidation, acetalization and oxidation. Bulky steric sensors at the anomeric center could enhance the stereoselectivity of the dioxirane epoxidation and one of the uloses performed with good enantioselectivity towards trans-stilbene (up to 90% ee). However, the catalysts decomposed during the epoxidation and the maximum chemical yield was only 13% under the basic conditions. Three l -threo-3-uloses could overcome the decomposition problem based on the electron withdrawing effect of the ester group(s) α to the ketone functionality. The best chemical yield was up to 93% using a ketone with two flanking ester groups. One of the improved uloses displayed moderate enantioselectivity towards trans-disubstituted and trisubstituted alkenes (40–68% ee).

Synthetic studies on zoapatanol: Construction of oxepanes via an intramolecular 1,3-dipolar cycloaddition strategy

Abstract The nitrones derived from β-allyloxyaldehydes with a β-quaternary centre cyclized to give six- instead of seven-membered O -heterocycles exclusively whereas a nitrile oxide derived from a γ-allyloxyaldehyde with a γ-quaternary center cyclized to yield an oxepane ring as the sole product. Using the latter intramolecular nitrile oxide cycloaddition as the key step, optically active oxepane 5 , which is a suitable intermediate for a synthesis of zoapatanol 1 , has been constructed from d -glucose.

Intramolecular direct Aldol reactions of sugar diketones: Syntheses of valiolamine and validoxylamine G

A new and stereoselective intramolecular direct aldol reaction of diketones derived from carbohydrates has been developed to construct carbocycles with D-gluco-, D-galacto-, D-manno-, and L-ido-configurations. The stereochemical outcome of the aldol reaction of the diketone is dependent on the base used. Transformation of D-gluco-aldols readily affords valiolamine which also constitutes a formal synthesis of voglibose. Facile conversion of D-gluco-cyclohexanones into validoxylamine G has been achieved in 12 steps with 15.1% overall yield from D-glucose.

Stereocontrolled syntheses of (-)-goniofufurone and (-)-8-epi-goniofufurone

Abstract The absolute configurations of natural goniofufurone and 8- epi -goniofufurone are shown to be 2 and 4 respectively by unambiguous syntheses of their enantiomers 1 and 3 from d - glycero - d - gulo -heptono-γ-lactone 7 involving an intramolecular Michael reaction as the key step. The diol 6 , readily availble from d - glycero - d - gulo -heptono-γ-lactone, has been converted by six sequential reactions (acetylation, hydrolysis, deacetylation, glycol cleavage, Wittig reaction, and hydrolysis) into the γ-lactone 5 which underwent an intramolecular Michael reaction to yield (-)-goniofufurone 1 . Likewise reactions of the monoacetate 12 gave (-)-8- epi -goniofufurone 3 .

Sulphate ester of trans-4-hydroxypipecolic acid in seeds of Peltophorum

Abstract An acidic compound isolated from seed of the legume Peltophorum africanum has been characterised on the basis of FAB-MS, EIMS, 13 C and 1 H NMR as trans -4-hydroxypipecolic acid-4-sulphate. This is the first naturally occurring sulphate ester of a non-protein amino acid to be described. The possible systematic significance of the distribution of the ester within Peltophorum and related genera is considered.