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:

1) Functional gps attached to steroidal nucleus 2) Overall shape conformation (dictated by

stereochemistry)

SteroidsModified triterpenoids Tetracyclic of lanosterols lacking 3 CH3 gps @ C4 & C14Cholesterol fundamental structure , modifications of the side chain produce large no. of compTwo important groups of naturally occurring steroids: steroidal hormones & Cardiac glycosides

Cholesterol Triterpenoid

A B

C DA B

C D

HO

E17

12

34

56

7

89

10

11 12

13

14 15

16

1718

19

2021 22

23

2425 26

27

4

20

OH

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

OH

5O 4 Norethisterone

HC CHH19

OH

5O 4 Norgestrel

H CH

CH

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 5 step reaction!]

• Other raw materials: sitosterol, stigmasterol

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

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

O

O

O

22

25

26

3Diosgenin

O

OO

OH

OHOH

OHOH

O

O

D-Gluc

L-Rha

L-Rha

1 4

1 2

Alpha

Alpha

Dioscin

SpirostaneBeta 1

Sterols

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

HO 5 6Cholesterol

ErgosterolSitosterol

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)

HO 5 6Cholesterol

HOH

98 14

Lanosterol

H

3 CH3+2 H

Medicinal Value of Cholesterol • Cholesterol biosynthesis inhibited by HMG-CoA reductase in

mevalonate pathway e.g. lovastatin and derivativesCholesterol is primary source for semi-synthetic medicinal

steroidsNatural 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

Stigmasterol and sitosterolStigmasterol first isolated from calabar beans, then from soya bean oil

Both are raw materials for the semisynthetic production of steroids. Stigmasterol easily converted to progesteron which is in turn starting material for other steroids

HO

H

H

H

22 24

241242

STIGMASTEROLHO

H

H

H

22 24

SITOSTEROL

HH

RS

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

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

Vitamin D

HO

H

HO

UV

17

HO

HUV

17

HO

7-Dehydrocholesterol

Colecalciferol (Vit. D3)

Ergosterol

Ergocalciferol (Vit D 2)

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

Cardiac Glycosides Cardiotonic glycosidesHistory of Traditional Use:Arrow poisonsHeart drugsRx of dropsy (accumulation of H2O in the body)Modern Medicine Applications:Rx of CHF (+ve inotropic effect) Supra-ventricular fibrillation

Natural Sources

Botanical Origin:

Very limited distribution Mainly Asclepiadaceae & Apocynaceae Digitalis lanata, D. purpurea (fox gloves)

Scrophulariaceae الديجيتال Strophanthus kombe, S. gratus ApocynaceaeNerium oleander (Rose laurel) الدفلة ApocynaceaeHelleborus niger (Christmas Rose) Ranunclaceae

المجيد الميالد عيد زهرةUrginea maritima (Squill) Liliaceae العنصل Toad venoms

Chemistry-Pharmacology Relation

Therapeutic action depends on :1. Structure of aglycone2. Type & number of sugar units attached3. Pharmacological activity is due to the aglycone but

modified by nature of sugar @C34. Sugar for transportation & pharmacokinetics5. Biosynthesized from cholesterol through

shortening and cleavage of the side chain followed by oxidation and cyclyzation

Aglycone Classes• C23 & C24Characteristic of C. Glyc:1. A/B + C/D Cis2. B/C Trans3. 3β- OH, 14β- OH4. α,β- unsaturated lactone

ring @ C-175. Additional OH at C12&C166. C19:CH3/CH2OH/COOH 7. Glycosidic bond @ C-3 [Spirostane saponins co-occur

with cardenolide glycosides in D. purpurea]

O

HO

H

O

OH

H

H

Cardenolide (C 23)

12

3

4

5

6

78

910

1112

1314

15

16

1718

19

2120 22

23

HO

H OH

OH

H

O

O

2

3

4

56

8

9

1112

1314

15

16

1718

19

2120 22

2324

Bufadienolide (C24)

7

10

Cardenolide Lactone Ring

Bufodienolide Lactone Ring

Sugar moieties in cardiac glycosides

Glucose andRare/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, …

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

O

OH

OH

23

45

6

OH

D-Digitoxose

O

OH

OH

23

45

6

OCH3

O

OH

OH

23

45

6

OCH3OH

D-DigitaloseD-Cymarose

Digitalis purpurea glycosidesScrophulariaceae (Foxglove)

1ry Glycosides Series Aglycone

Purpureaglycoside-A 3β,-14β-diydroxylated

Digitoxigenin

Purpureaglycoside-B 3β,14β,16β-trihydroxylated

Gitoxigenin

Purpureaglycoside-E

(Glucogitaloxin)

16-formylgitoxigenin

Gitaloxigenin

Purpureaglycoside-A & Digitoxin

OO

O

O

O

OO

O

O

O

HO

HO

HOHOOH

HO OH

OH

14

3

1612

H

H

Purpureaglycoside A

D-glucose

D-digitoxose

3

HD-digitoxoseD-digitoxose

Digitoxin

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

Lanatosides1ry Glycosides

SeriesAglycone

Lanatoside-A3β,-14β-diydroxylated

Digitoxigenin

Lanatoside-B3β,14β,16β-trihydroxylated

Gitoxigenin

Lanatoside-C3β,14β,12β-trihydroxylated

Digoxigenin

Lanatoside-D3β,14β,12β,16β-tetrahydroxylated

Diginatigenin

Lanatoside-E16-formylgitoxigenin

Gitaloxigenin

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

Digoxin

OO

O

O

OO

O

O

HO

HO

HO

HOOH

14

3

1612

H

H

3

H

HO

D-digitoxoseD-digitoxose

D-digitoxose

Digoxin ProductionPharmaceutical 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

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

OO

O

O

O

OO

O

O

O

HO

HO

OHOOH

O

HO OH

OH

14

3

1612

H

H

Lanatoside-C

D-glucose

3-acetyl-D-digitoxose

3

H

HO

D-digitoxoseD-digitoxose

Acetyldigoxin

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↓

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

Proscillaridin A• Large number of cardiac glycosides of

bufadienolides class

Proscilaridin A

O

ORhamnose

O

OH

14

3

17