Synthesis And Action Mechanism Of Anti-Tumor Diosgenin Derivatives

Steroidal saponins draw much attention due to their diverse biological activities, especially their excellent anti-tumor activity. Due to the low content in plants and the complexity in isolation and purification, abundant saponin derivatives were semi-synthesized via modifications on the sugar chain and/or the aglycon of saponin molecular starting from commercially available aglycon, meanwhile several candidates bearing good anti-tumor property were obtained.First, we summarized that steroidal saponin can be subdivided into spirostanol saponin, furostanol saponin and cholesteric saponin, and the possibility of a concise chemical conversion was figured out. Then derivative preparation and anti-tumor activity of diosgenin, which is the most widespreading spirostanol aglycon in nature, were reviewed generally. The anti-tumor activity of steroidal saponin resulted from the collaboration of its aglycon and sugar moiety, therefore this paper should be divided into three parts. In the first part, the simple preparation of natural furostanol saponin from diosgenin was developed, which provided an easier method to modify the aglycon of steroidal saponin. The second part was related to the glycosylation of diosgenin, yielding a series of unnatural steroidal saponin, to discuss the influence of sugar moiety on its parent’s anti-tumor activity. In the third part, several bioactive groups were introduced into the amino group of diosgenyl glucosaminide, which showed that modification on the sugar moiety could affect the anti-tumor activity of steroidal saponin.The total synthesis of the two important furostanol saponin methyl protodioscin and icogenin was firstly reviewed, and their inefficiency was figured out. Therefore, we have developed a highly efficient E-ring opening reaction of spirostanol saponin by BF3-Et2O/Ac2O. Starting from diosgenin and applying this E-ring opening reaction, methyl protodioscin was synthesized in seven steps with a total yield of24%. During the synthesis of methyl protodioscin, we found that this E-ring opening reaction could be applied for the efficient synthesis of cholestane,22-OH furostan and22-OMe furostan. Consequently, we have also developed a direct F-ring opening reaction of spirostanol saponin by BF3-Et2O/TFA-HOAc. Applying this F-ring opening reaction, methyl protodiosgenin, which is the mutual aglycon of methyl protodioscin and icogenin, was prepared in three steps starting from diosgenin. After stability of glycosidic bond under the F-ring opening reaction condition was confirmed, icogenin was synthesized concisely starting from diosgenin by this F-ring opening reaction.A common disaccharide moiety from cytotoxic triterpenoidal saponin, namely a-L-rhamnopyranosyl-(1→2)-a-L-arabinopyranosyl was introduced to the3-OH of diosgenin, and glycosylation of the4-OH in both arabinose residue and rhamnose residue using six sugar donors provided six derivatives with branched sugar chain and six derivatives with linear sugar chain. In the in vitro cytotoxicity screening, compound65was found to have a strong inhibition on A549cells, and this compound was demonstrated to induce apoptosis in A549cells via extrinsic pathway through cell morphology observation, cell staining, DNA fragmentation assay, flow cytometric analysis and western blot.It is a common derivation of saponin by modifying its sugar moiety with bioactive groups. The substituents on the amino groups of diosgenyl glucosaminides could affect their anti-tumor effect significantly according to the previou research. According to this conclusion, three series of diosgenyl glucosaminides bearing cinnamoyl, urea and thiosemicarbazone groups on their amino groups were designed and synthesized, giving thirty-four saponin derivatives. The structure-activity relationships were summarized after the in vitro cytotoxicity screening, and we found that cinnamoyl groups were preferred comparing to the urea and thiosemicarbazone group, meanwhile the amount, position and style of substituent on the benzene ring in the cinnamoyl group could affect the anti-tumor activity and selectivity of its parent significantly. The toxicity on PBMC and mechanism inhibiting MCF-7cells of compound91c were studied. Compound91c show toxicity on PBMC, and the action mechanism research of compound91indicated that this compound induces apoptosis in MCF-7cells, but autophagy and necroptosis did not occur in the treated MCF-7cells.