(+)-proto-Quercitol, a natural versatile chiral building block for the synthesis of the α-glucosidase inhibitors, 5-amino-1,2,3,4-cyclohexanetetrols

An efficient synthesis of diastereomerically pure 5-amino-1,2,3,4-cyclohexanetetrols (6 and 11) and quercitol derivatives from naturally available (+)-proto-quercitol (1) is described. The stereochemistry of 1 is perfectly set up for regioselective protection of the hydroxy group which was further functionalized into the target aminocyclitol in a straightforward manner. The present approach provides a protocol for preparing aminocyclitols in large quantities. In addition, the absolute stereochemistry of (+)-proto-quercitol was addressed using the modified Mosher’s method. Of the synthesized aminocyclitols, 11 potentially inhibits α-glucosidase with an IC₅₀ value of 12.5 μM, which is 45 times greater than that of the standard antidiabetes drug, Acarbose^®.     

Lamesticumin G,a new α-glucosidase inhibitor from the fruit peels of Lansium parasiticum

A novel onoceranoid triterpene, named lamesticumin G (1) along with four known compounds (2–5) were isolated from the ethyl acetate extract of the fruit peels of Lansium parasiticum. The structure of lamesticumin G (1) was fully characterised using spectroscopic data. Lamesticumin G (1) inhibited α-glucosidase (maltase) with IC₅₀ value of 2.27 mM, while 2–5 showed no inhibition.     

New onoceranoid xyloside from Lansium parasiticum

A novel onoceranoid triterpene xyloside named methyl lansioside C (1) together with two known glycosides (2 and 3) were isolated from polar fraction of the fruit peels of Lansium parasiticum. The structure and absolute configuration of the new compound were established using extensive spectroscopic techniques as well as Mosher’s method. The antioxidant activity and α-glucosidase inhibitory effect of the isolated compounds were evaluated. Compounds 1 and 3 displayed moderate radical scavenging activity with SC₅₀ values of 14.5 and 13.7?mM, respectively. However, all isolated compounds exhibited no inhibition against α-glucosidase.     

Total Synthesis and Structural Revision of Antibiotic CJ‐16,264

The total synthesis and structural revision of antibiotic CJ‐16,264 is described. Starting with citronellal, the quest for the target molecule featured a novel bis‐transannular Diels–Alder reaction that casted stereoselectively the decalin system and included the synthesis of six isomers before demystification of its true structure.