Synthesis of 20S-protopanaxadiol β-D-galactopyranosides
20S-Protopanaxadiol (3β,12β,20S-trihydroxydammar-24-ene) 3-, 12-, and 20-O-β-D-galactopyranosides were synthesized for the first time. Condensation of 12β-acetoxy-3β,20S-dihydroxydammar-24-ene (1) and 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosylbromide (α-acetobromogalactose) (2) under Koenigs–Knorr conditions with subsequent removal of the protecting groups resulted in regio- and stereoselective formation of 20S-protopanaxadiol 3-O-β-D-galactopyranoside, an analog of the natural ginsenoside Rh2. Glycosylation of 12β,20S-dihydroxydammar-24-en-3-one (5) by 2 with subsequent treatment of the reaction products with NaBH4 in isopropanol and deacetylation with NaOMe gave 20S-protopanaxadiol 12- and 20-O-β-Dgalactopyranosides.
Chemical synthesis of saponins.
Saponins are a large family of amphiphilic glycosides of steroids and triterpenes found in plants and some marine organisms. By expressing a large diversity of structures on both sugar chains and aglycones, saponins exhibit a wide range of biological and pharmacological properties and serve as major active principles in folk medicines, especially in traditional Chinese medicines. Isolation of saponins from natural sources is usually a formidable task due to the microheterogeneity of saponins in Nature. Chemical synthesis can provide access to large amounts of natural saponins as well as congeners for understanding their structure-activity relationships and mechanisms of action. This article presents a comprehensive account on chemical synthesis of saponins. First highlighted are general considerations on saponin synthesis, including preparation of aglycones and carbohydrate building blocks, assembly strategies, and protecting-group strategies. Next described is the state of the art in the synthesis of each type of saponins, with an emphasis on those representative saponins having sophisticated structures and potent biological activities.
Holothurins B(2), B(3), and B(4), new triterpene glycosides from mediterranean sea cucumbers of the genus holothuria.
Triterpene glycosides of three species of the Mediterranean sea cucumbers Holothuria polii, Holothuria tubulosa, and Holothuria sp. were studied. Three new monosulfated biosides, holothurins B(2) (1), B(3) (2), and B(4) (3), along with the previously known holothurins A (4) and B (5) were isolated from the sea cucumber H. polii. Triterpene glycosides belonging to holothurin A and B groups were found in H. tubulosa, while only one individual glycoside, holothurin A (4), was isolated from Holothuria sp. Structures of new substances were elucidated on the basis of spectral data (2D NMR and MS). The significance of holothurins as chemotaxonomic markers of the animals belonging to the genus Holothuria and taxonomic status of some representatives of the holothurians studied are discussed.