Friedel—Crafts Acylation as a Quality Control Assay for Steroids

Abstract

The rapid Friedel-Crafts chromogenic acylation of alkene groups at ambient temperatures using a 25:1 mixture of 98% acetyl chloride and 70% perchloric acid is shown to have all the properties needed to serve as a potential quality control reagent that can be used to routinely discriminate among steroid analogs. Although ostensibly a non-selective reagent, from these and prior applications in terpenes and polyunsaturated acid esters, it is seen that the reaction is capable of discriminating bewteen geometric isomers and even enantiomers. The selectivity towards acylation of the alpha- over the beta-position at C-17 makes the method adaptable to screening for anabolic steroids. Reactions at that position produce the more unusual results, including a positive color reaction for alpha-methyltestosterone even though there is no alkene functional group in the vicinity of C-17. For molecules with more than one alkene, concurrent acylations are independent one from the other and, in the absence of any interferences, their spectral properties are found to be additive.

The Liebermann–Burchard Reaction: Sulfonation, Desaturation, and Rearrangment of Cholesterol in Acid

“…Although we have not identified the elusive color-producing species, our mechanistic insights and advances in methodology lay a sound foundation for future work. A resurrection of colorimetric assays is unlikely in clinical laboratories, but rapid and simple steroid assays continue to draw interest [26]. Some of the rearrangements observed for the LB and Salkowski reactions are similar to degradation pathways inferred from studies of sterol diagenesis under various geological conditions [27][28][29].…”

Simultaneous spectrophotometric and chemometric determination of lipids in synthetic mixtures and human serum

“…This so-called Purdie reagent had the extra selectivity of acylation of the a-over the ß-position at the C-17 carbon that enabled the differentiation of anabolic steroids. In that and a following study, it was also determined that if multiple unsaturated lipids are present, the resulting compounded spectrum is the simple addition of the weighted spectra for each of the components, assuming no extraneous interferences are present [3]. Figure 1 shows the molar absorptivity spectra for the analytes of interest in this serum sample study.…”

Recent Advances in the Analysis of Steroid Hormones and Related Drugs

“…This is the case with a paper where Friedel-Crafts acetylation of steroids followed by taking the UV spectrum enables interesting discrimination to be made between various isomeric derivatives. 34 Kinetic variants of the classical Blue Tetrazolium and phenylhydrazine 35 and isoniazid 36 reactions and their application to the analysis of corticosteroids in various pharmaceuticals are also worth mentioning.…”