Functionalized Spirocyclic Heterocycle Synthesis and Cytotoxicity Assay

Summary

Here, we describe a bioassay using 3-(4′,5′-dimethylthiazol-2′-yl)-2,5- diphenyltetrazolium bromide (MTT) to test previously synthesized spirocyclic oximes.

Abstract

Spirocyclic heterocycles have recently been reported in literature to be potential drugs for cancer therapy. The synthesis of these novel orthogonal ring systems is challenging. An efficient methodology to synthesize these compounds was recently published that described the solid phase synthesis in four steps rather than the previously reported five steps. The advantage of this shorter synthesis is the elimination of the use of toxic reagents. Low-loading Regenerating Michael (REM) linker-based resin was found to be crucial in the synthesis as high-loading versions prevented the addition of reagents containing bulky phenyl and aromatic side chains. The colorimetric 3-(4′,5′-dimethylthiazol-2′-yl)-2,5- diphenyltetrazolium bromide (MTT) assay was used to examine the cytotoxicity of micromolar concentrations of these novel spirocyclic molecules in vitro. MTT is readily available commercially and produces relatively fast, reliable results, making this assay ideal for these spirocyclic heterocycles. Orthogonal ring structures as well as furfurylamine (a precursor in the synthesis method containing a similar 5-member ring motif) were tested.

Introduction

Small-molecule inhibition of the interaction of E3 ubiquitin-ligase mouse double minute 2 homolog (MDM2) with p53 is known to restore p53-mediated induction of tumor cell apoptosis^1,2,3. MDM2 is a negative regulator of the p53 pathway and is often overexpressed in cancer cells^4,5,6,7,8,9. Recent crystallographic and biochemical studies have revealed that small molecules containing....

Protocol

NOTE: Several chemicals and biological reagents used in this protocol are toxic and carcinogenic. Consult relevant material safety data sheets (MSDS) prior to use. Use appropriate personal protective gears (Occupational Safety and Health Administration-approved safety goggles, proper gloves, lab coats, full-length pants, and closed-toe shoes) prior to starting the experiment. In addition, adopt appropriate safety practices when performing synthesis and handling toxic chemicals and reagents (fume hood).

1. Solid phase synthesis of spirocyclic heterocycles 6 and 7

NOTE: Synthesis was based on previously published wor....

Results

Spirocyclic oximes 6 and 7 were synthesized using a modified protocol (Figure 1). Michael addition of furfurylamine to an REM linker 1b afforded polymer-bound resin 2. The progress of the reaction was monitored by infrared (IR) spectroscopy by detecting the disappearance of the α,β-unsaturated ester at 1722 cm^-1 (Figure 3). Spirocyclic-bound resin 4 was formed from 2 via a transient intermediate 3. Methanolic hydrolysis of 4 produced 3-[(3E)-.......

Discussion

The synthesis of the spirocyclic compounds was based on previous research conducted by this laboratory, but with some modifications (Figure 1)^11,12. The progress of each reaction step was monitored by IR spectroscopy. Michael addition of the REM linker 1 with furfurylamine afforded polymer-bound 2 (IR 1722 cm^-1 → 1731 cm^-.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
CELLS
COS-7 cells (ATCC CRL-1651)	ATCC	CRL-1651	African green monkey kidney cells
CHEMICALS
1-Bromooctane	Sigma-Aldrich	152951	Alkyl-halide
Allylbromide	Sigma-Aldrich	337528	Alkyl-halide
Benzylbromide	Sigma-Aldrich	B17905	Alkyl-halide
Cisplatin	Cayman Chemical	13119	Cytotoxicity control
Dichloromethane (DCM)	Sigma-Aldrich	270997	Solvent
Dimethylformamide (DMF)	Sigma-Aldrich	227056	Solvent
Dimethylsulfoxide (DMSO)	Sigma-Aldrich	276855	Solvent
DMEM, high glucose, with L-glutamine	Genesee Scientific	25-500	Cell culture media
FBS (Fetal bovine serum)	Sigma-Aldrich	F4135	Cell culture media
Furfurylamine	Acros Organics	119800050	reagent
Iodomethane	Sigma-Aldrich	289566	Alkyl-halide
Methanol	Sigma-Aldrich	34860	Solvent
MTT ((3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide)	EMD Millipore	Calbiochem 475989-1GM	Reagent
Phosphate-buffered Saline (PBS)	Genesee Scientific	25-507	Cell culture media
REM Resin	Nova Biochem	8551010005	Polymer support; 0.500 mmol/g loading
trans-β-nitrostyrene	Sigma-Aldrich	N26806	Nitro-olefin reagent
Toluene	Sigma-Aldrich	244511	Solvent
Triethylamine (TEA)	Sigma-Aldrich	T0886	Reagent for beta-elimination
Trimethylsilyl chloride (TMSCl)	Sigma-Aldrich	386529	Reagent; CAUTION - highly volatile; creates HCl gas
GLASSWARE/INSTRUMENTATION
25 mL solid-phase reaction vessel	Chemglass	CG-1861-02	Glassware with filter
96 Well plate reader	Promega (Turner Biosystems)	9310-011	Instrument
AVANCE III NMR Spectrometer	Bruker	N/A	Instrument; 300 MHz; Solvents: CDCl3 and CD3OH
Thermo Scientific Nicole iS5	Thermo Scientific	IQLAADGAAGFAHDMAZA	Instrument
Wrist-Action Shaker	Burrell Scientific	757950819	Instrument