Cytotoxic activities of synthesized curcumin and 3,4-Difluorinated curcumin against HepG2, LU-1 and KB cancer cell lines

Abstract

Introduction: Natural curcuminoids isolated from turmeric (Curcuma longa L.) have been limited in number and the amount of substrates evaluated in semi-synthetic processes and biological tests. Currently, potent anticancer activities of curcuminoids have garnered increased attention such that a greater number of synthetic procedures of curcumin analogues have been developed for further biological evaluations. The fluorine substituent of fluorinated compounds is important for biological responses. However, natural products bearing fluorine have rarely been found. In the study herein, we employed an aldol condensation between 4-hydroxy-3-methoxybenzaldehyde/3,4- difluorobenzaldehyde and pentane-2,4-dione to synthesize the desired curcumin (Cur) and 3,4- difluorinated curcumin (3,4-DFCur). Their half-maximal inhibitory concentration (IC50) values against HepG2, LU-1 and KB cancer cell lines were then assessed.
 Methods: Pentane-2,4-dione was converted to enol form by using B2O3 before carrying out C-C coupling reactions with benzaldehyde analogues under basic conditions. The water scavenger was added to the reaction to capture the produced water. The reaction mixture was stirred at 70 ◦C. The reaction progress was monitored by thin layer chromatography (TLC). Crude products were purified by flash column chromatography (CC; SiO2, eluent: HEX/EA = 9/1!7/3). The chemical structures of the desired products were elucidated by 1H, 13C-NMR, HSQC and MS spectra. The anticancer activities of Cur and 3,4- DFCur against HepG2, LU-1 and KB cancer cell lines were determined using MTT method.
 Results: Under reasonable reaction conditions, the yields for the coupling reactions were 53 and 72% for Cur and 3,4-DFCur, respectively. The stable enol tautomer of 1,3-diketone and the trans-configuration in a seven-carbon chain of product skeletons were assigned by 1H-NMR spectra. All synthesized products showed anticancer activities, with Cur exhibiting higher inhibitory activities when compared with 3,4-DFCur. Cur and 3,4-DFCur are Michael Acceptors; their cytotoxic activities could be attributed to the inhibition of glutathione S-transferase, a detoxification enzyme, by forming glutathionyl adducts. The decreased inhibitory capacities of 3,4-DFCur were due to the effect of fluorine which results in the unfavorable formation of reactive radicals and an increase in lipophilicity.
 Conclusions: Curcumin and 3,4-difluorinated curcumin were completely synthesized in 53% and 72% yields. The synthetic procedure is applicable for synthesizing curcumin derivatives bearing various substituents on the aromatic rings, i.e., not limited to methoxy (-OCH3) and hydroxy (- OH) groups. Unexpectedly, the presence of fluorines in 3,4-DFCur led to lower cytotoxic activities against cancer cell lines. Our results provide greater insight on the structure-activity relationship of curcumin analogues against cancer cell lines.

Synthesis and cytotoxicity of substituted aromatic curcuminoids against human oral epidermal carcinoma-KB cell line

“…Target curcuminoids (1-6) were synthesized following the published procedure from literature in 48-76% yields 12,13,18,19 (Table 1). Chemical structures were elucidated by NMR and MS spectra (see the Supporting Information for 1 H, 13 C-NMR, HSQC, and MS spectra). All synthesized compounds were evaluated for cytotoxicity against human oral epidermal carcinoma-KB cell line using MTT method.…”

“…The published procedurewas used to carry out the synthetic procedure of curcuminoids (1-6) bearing various substituents on aromatic rings 12,13,18,19 (Figure 1). A mixture of boron oxide (10.0 mmol) and pentane-2,4-dione (10.0 mmol) in ethyl acetate (20.0 mL) was stirred at 70 • C for 1 h in a 100-mL two-neck round-bottom flask to yield the solution of acetylacetone-borate complex.…”

“…Curcumin (1), a constituent of turmeric powder derived from the rhizome of C. longa, is an attractive compound with broad-spectrum capacities including anti-oxidant 5 , anti-inflammatory 6 , and antitumour 7 activities. In particular, many studies reported that curcumin exhibited anti-cancer activity in a wide range of human cancers [8][9][10][11][12][13][14][15] . In addition, curcumin is pharmacologically safe as large quantities of curcumin, up to 10 g per day, can be consumed without inflicting toxicity 16 .…”

“…To overcome these limitations, chemical modification of the curcumin structure is one of the promising approaches to explore curcumin-based analogs, which improve the therapeutic profile of the mother compound [8][9][10][11][12] . Structure-activity relationship (SAR) analysis on curcumin analogs revealed that the aromatic ring and its substituents are necessary for biological activities [10][11][12][13] . In view of this, benzaldehyde analogs bearing various functional groups in the phenyl ring were selected as starting materials to condense with pentane-2,4-dione under basic conditions to afford analogs of curcumin [10][11][12][13]18,19 .…”

“…Structure-activity relationship (SAR) analysis on curcumin analogs revealed that the aromatic ring and its substituents are necessary for biological activities [10][11][12][13] . In view of this, benzaldehyde analogs bearing various functional groups in the phenyl ring were selected as starting materials to condense with pentane-2,4-dione under basic conditions to afford analogs of curcumin [10][11][12][13]18,19 . Within this framework, curcumin analogs containing hydroxy/methoxy/fluorine groups on phenyl rings were synthesized in our work, and their in vitro anticancer activities against oral cancer cells (KB) were assessed.…”