Structural Optimization and Biological Screening of a Steroidal Scaffold Possessing Cucurbitacin‐Like Functionalities as B‐Raf Inhibitors

Abstract

Inhibition of the mitogen-activated protein kinase (MAPK) pathway by targeting the commonly occurring mutated B-Raf in melanoma has become a practical method for the development of drugs and drug candidates. In order to expand upon the currently reported structural scaffolds used to target the MAPK pathway, molecular docking studies led to the installation an α,β-unsaturated ketone side chain, related to the cucurbitacin class of natural products, on to an estrone core via an aldol condensation reaction, along with installation of the Δ(9,11) olefin to assemble what has been defined as a pseudo-cis configuration at the B/C ring juncture. Combination of these cucurbitacin-like features resulted in a compound with an enhanced biological profile against the A-375 mutant B-Raf cell line, in regards to their cytotoxicity and inhibitory activity toward phosphorylated extracellular-signal-regulated kinase (ERK).

Biological screening of cucurbitacin inspired estrone analogs targeting mitogen‐activated protein kinase (MAPK) pathway

“…Installation of the Δ9, 11 olefin at the B/C ring juncture of the steroidal skeleton to attain the pseudo‐cis configuration using 2, 3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) was previously described to mimic the cis configuration of cucurbitacin skeleton . The separated diastereomers MH‐1 and MH‐2 exhibited inhibition concentrations (IC 50 ) against mutant B‐Raf (A‐375) melanoma cell lines, ranging from 19.70 to 29.58 μ m , compared to their previously reported precursors, possessing enone system, ranging from 26.80 to 30.74 μ m .…”

“… Synthesis of (1): Compound (1) was synthesized according to Reference[15] Synthesis of (2): Compound (2) was synthesized according to Reference[15] Synthesis of (3): Compound (3) was synthesized according to Reference Synthesis of (4): Compound (4) was synthesized according to Reference …”

“…Due to the structural sophistication of cucurbitacins, estrone was used as a starting structure to be further optimized and used to install cucurbitacins' side chain and installation of double bond across the B/C ring juncture, followed by biological screening toward melanoma cell lines and their inhibitory effect for ERK phosphorylation . The main complications associated with cucurbitacins were due to the presence of 23, 24 α, β‐unsaturated ketone side chain that can undergo irreversible Michael addition, resulting in lack of selectivity interacting with different molecular targets, mutagenesis, and possibly carcinogenesis .…”

“…[11] Due to the structural sophistication of cucurbitacins, estrone was used as a starting structure to be further optimized and used to install cucurbitacins' side chain and installation of double bond across the B/C ring juncture, followed by biological screening toward melanoma cell lines and their inhibitory effect for ERK phosphorylation. [12] The main complications associated with cucurbitacins were due to the presence of 23, 24 α, β-unsaturated ketone side chain that can undergo irreversible Michael addition, resulting in lack of selectivity interacting with different molecular targets, mutagenesis, and possibly carcinogenesis. [13,14] Our main goal is to maintain a balance between the elimination of the enone system via installation of functional groups by symmetric Michael addition reaction and keeping the biological activity toward MAPK pathway, followed by further validation using in silico molecular modeling to investigate the potential binding affinity of the designed analogs toward ATP catalytic domain of B-RAF receptor, as shown in Figure 2.…”

“…Synthesis of (1): Compound (1) was synthesized according to Reference [15] Synthesis of (2): Compound (2) was synthesized according to Reference [15] Synthesis of (3): Compound (3) was synthesized according to Reference [12] Synthesis of (4): Compound (4) was synthesized according to Reference [12] MH-1a/b: To a stirred solution of 4-methylthiophenol (0.116 g, 0.94 mmol) in petroleum ether (4.0 ml) was added Et 3 N (0.127 ml, 0.94 mmol). This reaction mixture was then added to a solution of alkyl enone 1 (0.20 g, 0.468 mmol) dissolved in petroleum ether (4 ml), followed by stirring for 24 hr.…”