Androgen receptor modulators

These are non-steroidal small molecules between roughly 290 and 530 daltons. They carry no amide backbone, so the 214 nm detection that underpins every peptide purity figure has nothing specific to detect and reports mostly solvent. Purity is measured at the compound's own ultraviolet maximum, established from the reference standard rather than assumed.

A molecule this size gives one singly charged ion, not the multiply charged envelope a peptide gives, so there is nothing to deconvolute and no charge series to report. What matters instead is polarity. The aryl propanamides carry cyano and nitro groups and respond in negative electrospray; the basic amines and the spiroindoline respond in positive. A screen run in one polarity is blind to part of its own compound list, and a non-detect from such a screen is not evidence of absence.

There is no counter-ion determination and no net peptide content, because neither concept applies. Content is assay against a certified reference standard, or where no standard for the compound exists, quantitative NMR against a certified standard of a different substance entirely.

The cheap compounds are substituted for the expensive ones, and the substitutes are frequently not modulators at all: a growth hormone secretagogue, a PPAR delta agonist and a REV-ERB agonist are among the substances most often found in products labelled as something else. Because they act on different receptors, they are grouped together only by marketing, and a method built around that grouping rather than around the chemistry misses them.

Isotope patterns do a large share of the work at no cost. A single chlorine gives the molecular ion a satellite two daltons up at about a third the height of the main peak, and two sulfurs give one at about nine percent. Compounds whose names differ by a single digit differ in whether that satellite exists, so its presence or absence excludes candidates before any standard is consulted.

The rest is mass. Two PPAR delta agonists in wide circulation differ by one aromatic fluorine, 18 daltons, which barely shifts reversed-phase retention and is unmistakable on a spectrum. Two REV-ERB agonists share an entire chromophore and fragmentation core and differ by 41 daltons. In both pairs, identity established from retention time has established nothing.