Synthesis of acetates of gomphogenin and gomphoside and evaluation of structure-activity relationships

Antiproliferative activity of cardenolides on cell line A549: structure-activity relationship analysis

Since the beginning, natural products have represented an important source of bioactive molecules for cancer treatment. Among them, cardenolides attract the attention of different research groups due to their cardiotonic and antitumor activity. The observed biological activity is closely related to their Na+/K+-ATPase inhibition potency. Currently, the discovery of new compounds against cancer is an urgent need in modern pharmaceutical research. Thus, the aim of this work is to determine the physicochemical properties and substituent effects that module the antiproliferative activity of cardenolides on the human lung cancer cell line A549. We build and curate a library with results obtained from literature; molecular descriptors were calculated in PaDEL software, and SAR/QSAR analysis was performed. The SAR results showed that cardenolides were sensitive to modifications in C and D steroidal ring and required substituent groups with the function of hydrogen bond acceptor at the C3 position. QSAR models to doubly linked-type cardenolides indicated that properties as lipoaffinity and atoms with the capacity to be hydrogen bond acceptors are involved in the increment of antiproliferative activity on A549 cell line. In contrast, the presence and position of very electro-negative atoms on the molecule decreased the antiproliferative effect on A549 cells. These results suggest that the antiproliferative capacity of cardenolides on the cell line A549 is strongly related to substituent groups on the C3 position, which must not be carbohydrate. Additionally, the steroidal rings C and D must remain without modifications.

Synthesis of Analogues of (+)-Gomphoside, a Potent HIF-1 Inhibitor and Cardenolide

The milkweed bush Gomphocarpus fruticosus R.Br. found in Australia contains the steroidal glycoside (+)-gomphoside, its derivatives (-)-3'-dehydrogomphoside and (+)-3'- epi-gomphoside, as well as other glycoside compounds. The key structural features of these unique herbal agents are bislinked steroid to sugar linkages. (+)-Gomphoside is an extremely potent cardenolide and highly effective Hypoxia-Inducible Factor (HIF)-1 inhibitor. In addition, (+)-gomphoside exhibits strong cytotoxicity on human breast cancer cell lines.

The syntheses of (+)-gomphoside analogues with modified steroidal D rings are described here. The syntheses started with glycosylation of (+)-(2α,3β,5α)-2,3-cholestanediol with benzoylated 2-keto sugar bromides, promoted by silver carbonate. Two regioisomeric glycosides with bent up and bent down ring anellation geometry were obtained, because of the two hydroxyl groups in the diol. Modification of the sugar ring of these glycosides by base-induced elimination of benzoic acid yielded (-)-3'-dehydrogomphoside analogues. The analogues of (+)-gomphoside and (+)-3'- epi-gomphoside were then obtained by stereoselective reduction of the 3'-carbonyl function. Compared to natural (+)-gomphoside, these analogues have the following unique structural features: a steroidal D ring with C8H17-alkyl chain instead of an exocyclic butenolide moiety, a different configuration at bridgehead carbon-14, and lack of a hydroxyl group at this position. The resulting altered chemical properties make them interesting structures for pharmacological evaluation and they are potentially suitable candidates for the development of new inhibitors in cancer therapy.

Synthesis and biological evaluation of 2-hydroxy derivatives of digitoxigenin and 3-epidigitoxigenin

The four stereoisomers of the 2-hydroxy derivatives of digitoxigenin and 3-epidigitoxigenin have been synthesized, their structures established by NMR, and their binding affinity for the digitalis receptor on Na+, K(+)-ATPase evaluated. These derivatives showed lower affinities than the parent compounds. The hydrophilic hydroxy groups in the alpha position are more detrimental to the affinity than hydroxy groups in the beta position.

Partial synthetic derivatization of canrenone and characterization of its impact on the inhibitory effect on Na+/K(+)-ATPase activity in human heart muscle

To improve the weak inhibitory effect of 3-oxo-17 alpha-pregna-4,6-diene-21,17-carbolactone (canrenone, II) on Na+/K(+)-ATPase activity in human heart muscle, we have investigated the impact of hydrogenation, reduction, glycosidation, and the introduction of a 3-sulfonamido residue on the inhibitory potency of canrenone. The greatest increase in potency (> 20 times) was found for 3 beta-(alpha-L-rhamnopyranosyloxy)-5 beta, 17 alpha-pregnane-21, 17-carbolactone (IX). The 3-O-glycosides IX-XI are the first representatives of C/D-trans steroids with effector-receptor complex decay half-times longer than those of therapeutically used cardenolides.