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Steroids

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Cholesterol serves as a vital precursor for various steroid hormones, including vitamin D and corticosteroids. Its structure comprises a modified steroid skeleton, with angular methyl groups at carbon positions C-10 and C-13. The biosynthesis of cholesterol involves an enzymatic conversion to 7-dehydrocholesterol, which can be transformed into vitamin D3 when exposed to sunlight. This overview also highlights the significance of bile acids in digestion and the roles of sex hormones like testosterone and estradiol in reproduction.

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Steroids

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  1. Steroids

  2. Steroids

  3. Steroid A/B and B/C Rings Resemble Decalin

  4. Steroid B/ C, and C/D rings are trans fused Methyl groups at C-10 and C-13 are “angular” methyl groups

  5. Cholesterol

  6. CH3 CH3 CH3 CH3 CH3 H H H HO Structure of Cholesterol • Cholesterol has the fundamental steroid skeleton modified as shown.

  7. Biosynthesis of Cholesterol

  8. CH3 CH3 CH3 CH3 CH3 H H H HO Cholesterol

  9. Vitamin D

  10. CH3 CH3 CH3 CH3 CH3 H H H HO Cholesterol • Cholesterol is the precursor to vitamin D. • Enzymes dehydrogenate cholesterol to introduce a second double bond in conjugation with the existing one. The product of this reaction is called 7-dehydrocholesterol.

  11. 7-Dehydrocholesterol CH3 CH3 • Sunlight converts 7-dehydrocholesterol on the skin's surface to vitamin D3. CH3 CH3 CH3 H H HO

  12. Vitamin D3 CH3 CH3 • Insufficient sunlight can lead to a deficiency of vitamin D3, interfering with Ca2+ transport and bone development. Rickets can result. CH3 CH3 H HO

  13. Bile Acids

  14. CH3 CH3 CH3 CH3 CH3 H H H HO Cholesterol • Oxidation in the liver degrades the cholesterol side chain. Cholic acid is the most abundant of the bile acids.

  15. O CH3 HO OH CH3 CH3 H H H HO OH H Cholic Acid • Salts of cholic acid amides (bile salts) act as emulsifying agents to aid digestion.

  16. Corticosteroids

  17. CH3 CH3 CH3 CH3 CH3 H H H HO Cholesterol • Enzymatic degradation of the side chain and oxidation of various positions on the steroid skeleton convert cholesterol to corticosteroids.

  18. Cortisone O OH CH3 • Corticosteroids are involved in maintaining electrolyte levels, in the metabolism of carbohydrates, and in mediating the allergic response. O OH CH3 H H H O

  19. Sex Hormones

  20. OH H3C H3C H H H O Testosterone • Testosterone is the main male sex hormone.

  21. Estradiol OH H3C • Estradiol is a female sex hormone involved in regulating the menstrual cycle and in reproduction. H H H HO

  22. O H3C H3C H H H O Progesterone • Supresses ovulation during pregnancy.

  23. Synthetic Steroids

  24. Recognizing Lipids: Structural Differences

  25. Question • Which of the triglycerides below is optically active? • A) 1 and 3 B) 2 and 3 E) none • C) 3 only D) 1, 2, and 3

  26. Question • Misoprostol is classified as a • A) terpene. B) wax. • C) steroid. D) prostaglandin.

  27. Question • The backbone of cephalosporin P is classified as a • A) prostaglandin. B) steroid. • C) cholesterol. D) sesterpene.

  28. Question • Farnesol is classified as a • A) monoterpene. • B) sesquiterpene. • C) diterpene. • D) triterpene.

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