Stereoselective Synthesis and Antiproliferative Activities of Tetrafunctional Diterpene Steviol Derivatives

Synthesis and medicinal chemical characterisation of antiproliferative O,N-functionalised isopulegol derivatives

Benzylation of isopulegol furnished O-benzyl-protected isopulegol, which was transformed into aminodiols via epoxidation followed by ring opening of the corresponding epoxides and subsequent hydrogenolysis. On the other hand, (-)-isopulegol was oxidised to a diol, which was then converted into dibenzyl-protected diol derivatives. The products were then transformed into aminotriols by using a similar method. The antiproliferative activity of aminodiol and aminotriol derivatives was examined. In addition, structure-activity relationships were also explored from the aspects of substituent effects and stereochemistry on the aminodiol and aminotriol systems. The drug-likeness of the compounds was assessed by in silico and experimental physicochemical characterisations, completed by kinetic aqueous solubility and in vitro intestinal-specific parallel artificial membrane permeability assay (PAMPA-GI) measurements.

Stereoselective synthesis and antiproliferative activity of allo-gibberic acid-based 1,3-aminoalcohol regioisomers

A new library of allo-gibberic acid-based aminoalcohol regioisomers was synthesised stereoselectively starting from commercially available gibberellic acid, which yields allo-gibberic acid under mild acidic conditions. The successful formation of hydroxymethyl ketone derivative 5, by acid-mediated rearrangement of previously prepared epoxide, paved the way to obtain the desired 1,3-aminoalcohols through Schiff base formation. To obtain the desired regioisomers, the primary alcohol functionality of 5 was subjected to mesylation, then replaced with either primary amine or sodium azide. The formed azide derivative was subjected to either CuAAC reaction to obtain 1,2,3-triazoles or underwent Pd-catalysed hydrogenolysis to obtain primary aminoalcohol, which was further transformed into 1,3-aminoalcohols by reductive alkylation. All prepared aminoalcohols were identified in a satisfactory manner using modern spectroscopic techniques and assessed for their antiproliferative activity against a panel of human cancer cell lines. The antiproliferative effects of the prepared compounds were assayed by in vitro MTT method against a panel of human cancer cell lines (HeLa, SiHa, A2780, MCF-7 and MDA-MB-231). A significant difference was observed in the antiproliferative activity between the regioisomers. Some compounds exerted outstanding activities against the malignant cells with limited action on fibroblasts, indicating considerable cancer selectivity.

F16 Hybrids Derived from Steviol or Isosteviol Are Accumulated in the Mitochondria of Tumor Cells and Overcome Drug Resistance

Steviol and isosteviol were prepared from the commercially available sweetener stevioside and converted into lipophilic F16 hybrids. Their cytotoxicity was determined in SRB assays and showed to depend on both the substitution pattern of the aromatic substituent as well as on the spacer length. Therefore, compound 25 held an IC50 (A2780) of 180 nM, thus surpassing the activity of comparable rhodamine hybrids. Several of the compounds were also able to overcome drug resistance in the A2780/A2780cis model. Extra staining experiments showed a similar subcellular accumulation pattern of the F16 hybrids as a well-established mitocan, hence proving preferential mitochondrial accumulation but also some other accumulation in other cellular areas.

Stereoselective Synthesis and Antiproliferative Activity of Steviol-Based Diterpene 1,3-Aminoalcohol Regioisomers

A series of novel diterpene-type 1,3-aminoalcohols and their regioisomers have been synthesised from natural stevioside in a stereoselective manner. The key intermediate β-keto alcohol was prepared using Wagner-Meerwein rearrangement of the epoxide derived from steviol methyl ester. The primary aminoalcohol was formed via Raney-nickel-catalysed hydrogenation of an oxime, and a versatile library of aminoalcohols was synthesised using a Schiff base with the primary amines. The aminoalcohol regioisomers were prepared from the mesylate of the β-keto alcohols. The corresponding primary aminoalcohol was formed via the palladium-catalysed hydrogenation of hydroxyl-azide, and click reactions of the latter were also carried out. The new compounds were characterised using 1D- and 2D-NMR techniques and HRMS measurements. The in vitro investigations showed high inhibition of cell growth in human cancer cell lines (HeLa, SiHa, A2780, MCF-7 and MDA-MB-231) in the case of naphthalic N-substituted derivatives. The antiproliferative effects were assayed using the MTT method.