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Steroids

Steroids. Wide range of biologically active natural products e.g. sterols, steroidal saponins, cardioactive glycosides, bile acids, corticosteroids, mammalian sex hormones Different activities of compounds with common structural skeleton is attributed partially to:

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Steroids

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  1. Steroids • Wide range of biologically active natural products e.g. sterols, steroidal saponins, cardioactive glycosides, bile acids, corticosteroids, mammalian sex hormones • Different activities of compounds with common structural skeleton is attributed partially to: • Functional gps attached to steroidal nucleus • Overall shape conformation (dictated by stereochemistry)

  2. Steroids Modified triterpenoids Tetracyclic of lanosterols lacking 3 CH3gps @ C4 & C14 Cholesterol fundamental structure , modifications of the side chain produce large no. of comp Two important groups of naturally occurring steroids: steroidal hormones & Cardiac glycosides Cholesterol Triterpenoid

  3. Medicinal Value of Plant Steroids • Important source of steroidal drugs • Minor % prepared from animal steroids & total synthesis • Norgestrel, C13 ethyl, totally synthetic (nothing in nature like this structure) • Aromatic steroids & C19 nor steroids are animal e.g. Norethisterone

  4. Steroidal Saponins • Same triterpenoidal saponins characters • Less widely distributed in nature • Plant families Dioscoreaceae, Liliaceae, Agavaceae • Sapogenins 27 Carbons • Side chain of cholesterol modified to spiroketal or hemiketal • All have C25 stereoisomerisation • Sugars @ C-3 & some @ C-26 • Less sugar molecules (Triterpenoidal saponins??) • > sugars result in > haemolytic effect • Raw material for the partial synthesis of steroidal hormones: ”Marker degradation”[Diosgenin →Progesteron; ONLY 5step reaction!] • Other raw materials: sitosterol, stigmasterol

  5. Dioscorea (Dioscoreaceae) • D. alata & D. esculenta, D. rotundata edible • Roots of some spp are rich in steroids considered bitter & inedible (Excellent source for drug manufacture) • Diosgenin is major sapogenin (60% of steroidal production derived from diosgenin) • Powdered Dioscorea (wild yam) root or extract as Rx for menopause (alternative to HRT) efficacy ???? • Diosgenin conversion in humans to progesterone

  6. Diosgenin • The aglycone of the saponin from the tubers of Dioscorea spp (Dioscoreaceae) e.g. D. composita, D. mexicana • Important source for pharmaceutical industry as the starting molecule of steroids synthesis e.g. progesterone, testosterone, cortisone • Microorganisms introduce OH gp at specific position in steroid skeleton

  7. Sterols • Zoosterols: side chain 8C→Cholesterol • Mycosterols: side chain 9C →Ergosterol • Phytosterols: side chain 10C →Sitosterol Sitosterol Ergosterol

  8. Cholesterol • Principle animal sterol • Alcoholic triterpene (lanosterol) converted to cholesterol • Essential constituent of cell membranes in all animal tissues • Maintains membrane fluidity, microdomain structure & permeability • Precursor for steroid hormones, bile acids, Vit. D & lipoproteins “LDL & HDL” (proteins + phospholipids carrying cholesterol in blood to tissues) • Associated with cardiovascular diseases, atherosclerosis, hypercholesterolaemia, gallstone diseases (mostly cholesterol precipitated from bile)

  9. Medicinal Value of Cholesterol • Cholesterol biosynthesis inhibited by HMG-CoA reductase in mevalonate pathway e.g. lovastatin and derivatives Cholesterol is primary source for semi-synthetic medicinal steroids Natural sources for industry: • Brains and spinal cords of slaughtered cattle (by-product of meat industry) • Extracted lanolin & fatty layer of sheep’s wool (lanolin saponification provides alcohol fraction 34% cholesterol + 38% lanosterol/dihydrolanosterol • Wool alcohols are used as ointment base

  10. Stigmasterol and sitosterolStigmasterol first isolated from calabar beans, then from soya bean oilBoth are raw materials for the semisynthetic production of steroids. Stigmasterol easily converted to progesteron which is in turn starting material for other steroids

  11. Sitosterol • Analogue of stigmasterol with saturated side-chain • Sources: soya-bean and oils e.g. maize oil • Can not be degraded using chemical methods (no double bond side chain) • Microbial degradation • Starting molecule for sex hormone synthesis especially 19-norsteroids & spironolactones • Topical products for eczema, dry skin, burn scars • Hypocholesterolemic properties

  12. Vitamin D • Derived from Δ5,7-sterols • Chemically related to steroids (ring B open) • Cholecalciferol= Vit D3 from liver, milk, butter, fish-liver; skin of man! • Ergocalciferol= Vit D2 by UV radiation of ergosterol from yeast, overirradiation produces toxic substances: Toxisterols • Vit D essential for the utilization of Ca and P • Overdose: renal calculi, metastatic calcification

  13. Vitamin D

  14. Vit D • Vit D2 + Lumisterol → Vit D1 • Ergosterol (Pro Vit D2)→ Vit D2 • 7-dehydrocholesterol → Vit D3 • 22:23 dihydro-Vit D2 → Vit D4 • 7-dehydro-sitosterol → Vit D5 • 7-dehydrostigmasterol → Vit D6 • 7-dehydrocampesterol → Vit D7

  15. Cardiac Glycosides Cardiotonic glycosides History of Traditional Use: Arrow poisons Heart drugs Rx of dropsy (accumulation of H2O in the body) Modern Medicine Applications: Rx of CHF (+veinotropic effect) Supra-ventricular fibrillation

  16. Natural Sources Botanical Origin: • Very limited distribution • Mainly Asclepiadaceae & Apocynaceae • Digitalis lanata, D. purpurea (fox gloves) Scrophulariaceae الديجيتال • Strophanthus kombe, S. gratus Apocynaceae • Nerium oleander (Rose laurel) الدفلة Apocynaceae • Helleborus niger (Christmas Rose) Ranunclaceae زهرة عيد الميلاد المجيد • Urginea maritima (Squill) Liliaceae العنصل • Toad venoms

  17. Chemistry-Pharmacology Relation Therapeutic action depends on : • Structure of aglycone • Type & number of sugar units attached • Pharmacological activity is due to the aglycone but modified by nature of sugar @C3 • Sugar for transportation & pharmacokinetics • Biosynthesized from cholesterol through shortening and cleavage of the side chain followed by oxidation and cyclyzation

  18. Aglycone Classes Cardenolide Lactone Ring • C23 & C24 Characteristic of C. Glyc: • A/B + C/D Cis • B/C Trans • 3β- OH, 14β- OH • α,β- unsaturated lactone ring @ C-17 • Additional OH at C12&C16 • C19:CH3/CH2OH/COOH • Glycosidic bond @ C-3 [Spirostane saponins co-occur with cardenolide glycosides in D. purpurea] Bufodienolide Lactone Ring

  19. Sugar moieties in cardiac glycosides Glucose and Rare/uncomon sugars: • 6-deoxysugars • 2,6-deoxysugars • Their 3-O-methylethers • i.e: L-rhamnose, D-digitoxose, D-digitalose, D-cymarose, D-diginose, D-sarmentose, …

  20. Glycones of cardiac glycosides • 2,6-dideoxyhexoses (digitoxose & cymarose) • 6-deoxyhexoses (L-Rhamnose & D-Digitalose) • 3-Methylether hexoses (Digitalose & Cymarose) • D-Glucose, D-Fructose in 1ry Glycosides

  21. Digitalis purpurea glycosidesScrophulariaceae (Foxglove)

  22. Purpureaglycoside-A & Digitoxin

  23. Chemistry of D. lanata leaves (Scophulariaceae) • Dried @ temp ≤ 60ºC to prevent glycosidic link hydrolysis • > 60ºC result in dehydration @ C14 (inactive 14-anhydro comp.) Cardiac glycosides: Fresh Plant: 1ry glycosides=Lanatosides A-E series (Aglycone + 3 digitixoses +Acetyl + Glucose) Dry Plant: 2ry Glycosides=Lanatosides loses terminal glucose (Aglycone + 3 digitixoses + Acetyl) • Aglycone: Cardenolides[C23] in both

  24. Lanatosides

  25. Differences between two Digitalis species • The primary glycosides are not identical since in D. lanata -even the aglycon is the same- there is an acetyl group attached to the third sugar on OH at C-3 • Hydrolysis of the terminal glucose in D. lanata yields Acetyldigitoxin, acetylgitoxin, acetyldigoxin, acetylgitaloxin while in D. purpurea: Digitoxin, gitoxin, gitaloxin • Digoxigenin and its glycosides found only in D. lanata (Lanatoside C) • Digitoxin is the main secondary glycoside of D. purpurea while digoxin is the main secondary glycoside of D. lanata

  26. Digoxin

  27. Digoxin Production Pharmaceutical industry: Deacetylated the 2ry glycoside from dry leaves of D. lanata to produce digoxin OR • Terminal glucose is removed first then deacetylate 2ry glycoside from fresh plant • Deacetylation first then hydrolysis of terminal glucose is a 2nd option

  28. Digoxin • Lanatoside-C hydrolysed into acetyldigoxin by the action of β-glucosidase • Digoxin is the deacetylated derivative of 2ry glycoside from Lanatoside-C Rx CHF & atrial fibrillation

  29. Medicinal Applications • Illegal to sell crude drug or extracts of Digitalis (bacterial contamination of the leaves) • Digitalization is usually required • Drug monitoring through radioimmunoassay using specific antibodies • Sheep derived digoxin-specific antibody fragments for Rx of digoxin overdose • Digitoxin is highly lipid soluble, completely absorbed from GI tract (95%); halflife time :7days • Digoxin less lipid soluble, GI absorption 75%; halflife time:1.5 days • Polarity of cardiac glycosides↑, oral absorption↓

  30. Urginea maritima (Squill) • Bulb (formerly Scilla maritima) • Family Liliaceae • Used as expectorant as Gee’s linctus • Large doses toxicity (vomiting & digitalis-like action on heart) • Grows on Mediterranean & Canary Islands shores

  31. Proscillaridin A • Large number of cardiac glycosides of bufadienolides class Proscilaridin A

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