Useful approach to access germanicanes from betulin

Allobetulin and Its Derivatives: Synthesis and Biological Activity

“…Another obvious position for ring cleavage is the lactone bridge of 28-oxoallobetulin derivatives. This bridge is quite stable towards saponification, but LiAlH 4 reduction of the 3β-acetoxy derivative of 5 [ 108 ] or 28-oxoallobetulone ( 3 ) [ 25 , 30 , 109 ] gives a germanicanetriol derivative 67 which was further transformed to different germanicanes by selective acylation, oxidation and dehydration reactions [ 108 , 109 ]. The lactone ring of the protected 28-oxoallobetulone 22b was reductive cleaved with LiAlH 4 and after deprotection, 28-acetylation, dehydration with POCl 3 , saponification, and stepwise oxidation, moronic acid ( 68 ) and the reduced morolic acid 69 were obtained ( Figure 19 ) [ 41 ].…”

“…In vitro anticancer activity of saponins derived from 2 and 6 showed that the bioactivity for these glycosides was only moderate (IC 50 30–40 μM/L), as compared to the corresponding betulinic acid derivatives (IC 50 7.3–10.1 μM/L) [ 23 ]. The in vitro toxicity of 67 (human lung carcinoma or human colorectal adenocarcinoma assay) was comparable to that of betulinic acid or 5-fluorouracil [ 108 ]. Chacotrioside saponins such as 43 were fourfold superior to betulinic acid against human breast (MCF7) and prostate (PC-3) adenocarcimas cell lines.…”

Plant-derived triterpenoids and analogues as antitumor and anti-HIV agents

“…126 Capilliposide B ( 77 ), an epoxy-oleanane saponin isolated from Lysimachia capillipes , was cytotoxic against human A-2780 cells, with an IC 50 value of 0.08 µM. 127 In a semi-synthetic approach, 128,129 analogues were prepared from 77 and screened for cytotoxicity. However, only the 3- O -β- d -glucopyranoside (78) and 3- O -β- d -galactopyranoside ( 79 ) derivatives showed enhanced antitumor activity (IC 50 : 30–40 µm).…”

Advances in the Semi-Synthesis of Triterpenoids

“…The fused polycyclic skeleton of triterpenoids, as well as the embedded functionalities including alkenes and hydroxy groups, provide a structural basis for C-skeleton rearrangement, as exemplified by the transformation of lupanetype triterpenoid 79 into germanicane-type triterpenoid 81 (Scheme 13). 38 Taking advantage of the high propensity of the C20,29 double bond to generate cationic species at C20 under the effect of acidic conditions, 3-O-acetylated betulinic acid 79 underwent a smooth Wagner-Meerwein rearrangement under the promotion of FeCl 3 to deliver lactone 80, which was then reduced with lithium aluminum hydride (LAH) to provide 19-machaerocerol (81) (72%, 2 steps).…”