Synthesis and preliminary cytotoxicity evaluation of water soluble pentacyclic triterpenoid phosphonates

Abstract

Synthesis, solubility and cytotoxicity evaluation of anionic phosphonates derived from betulin, betulinic acid, oleanolic acid and ursolic acid is reported. Phosphonate moieties were successfully installed at terpenoid C28 by carboxylic acid deprotonation/alkylation sequence using (dimethoxyphosphoryl)methyl trifluoromethanesulfonate as alkylation reagent. Also, betulin-derived and ether-linked bis-phosphonate is obtained and characterized. After demethylation in the presence of TMSI the resulting phosphonic acids were transformed into their disodium salts. All target compounds display excellent water solubility, which was determined by qNMR in D₂O. Cytotoxicity tests were performed in different concentrations of each compound (10-50 µM) against human osteosarcoma cell line MG-63 and osteoblast precursor cell line MC3T3-E1. Improved aqueous solubility and low cytotoxicity profile of the newly designed triterpenoid phosphonates reveal high potential for various medicinal chemistry and pharmacological applications in the future.

Keywords: Aqueous solubility; Cytotoxicity; Pentacyclic triterpenoids; Phosphonates.

Fig. 1

Previously reported ionogenic PCTs, PCT-derived phosphonate conjugates and the original target molecules.

Fig. 2

Synthetic route for the preparation of phosphonic esters 4a-c.

Fig. 3

Synthesis of triterpenic acid derived sodium phosphonates 7b, c and 8a-c.

Fig. 4

¹H-NMR (500 MHz, D₂O) spectrum of 3-oxo-oleanolic acid-derived sodium phosphonate 7b (5 mg/mL).

Fig. 5

Synthesis of betulin-derived tetrasodium bis-phosphonate 12.