17hydroxyl

17hydroxyl is a shorthand reference to the presence of a hydroxyl (–OH) group at the 17th carbon atom of a steroid nucleus. In steroid chemistry and endocrinology, the position and stereochemistry of hydroxyl substituents (commonly 17α or 17β) profoundly influence biological activity, receptor binding, and metabolic fate.

As a structural descriptor, "17-hydroxy-" appears in the names of many endogenous and synthetic steroids. Examples include 17-hydroxyprogesterone and 17-hydroxypregnenolone, intermediates in adrenal and gonadal steroidogenesis, and 17β-estradiol, the primary active estrogen in humans. The distinction between 17α and 17β orientation is important: 17β-hydroxylation is characteristic of active estrogens, while modifications at 17α are used in synthetic steroid design.

Biologically, enzymes that act at carbon 17 are central to steroid biosynthesis. CYP17A1 (17α-hydroxylase/17,20-lyase) converts pregnenolone and progesterone into 17-hydroxylated precursors that lead to glucocorticoids and sex steroids. Genetic or acquired defects in these pathways can alter levels of 17-hydroxylated steroids and have clinical consequences, such as disorders of sexual development or forms of congenital adrenal hyperplasia.

In chemical nomenclature and pharmacology, noting a 17-hydroxyl group helps predict reactivity, metabolism, and pharmacodynamic properties of steroidal compounds.