secosteroids

Secosteroids are a class of steroids in which one of the rings of the steroid nucleus is cleaved, producing a seco (cut) structure. The name reflects this ring-opening modification, which distinguishes secosteroids from intact steroids. The most common form involves opening the B ring, yielding 9,10-secosteroids, though other ring cleavages such as 5,6-secosteroids also occur.

Natural secosteroids include the vitamin D family, with cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2) arising when ultraviolet radiation opens the B ring of sterol precursors. In humans, these compounds are further metabolized in the liver and kidneys to biologically active forms that help regulate calcium and phosphate homeostasis and influence bone health, immune function, and gene expression.

Beyond vitamin D, secosteroids are found in plants, fungi, and other organisms where ring opening yields diverse structures that can act as signaling molecules or defensive compounds. The exact roles of many non- vitamin D secosteroids vary, but they commonly affect enzyme activity or receptor interactions through their altered geometry and reactivity.

Applications and research: The vitamin D secosteroids are essential for mineral metabolism and skeletal integrity, and deficiency can lead to bone disorders such as rickets or osteomalacia. Other secosteroids are studied for potential pharmacological properties, including anti-inflammatory or anticancer effects, though evidence can be variable and regulatory assessment is ongoing. Structural diversity among secosteroids continues to inform medicinal chemistry and natural product research.