Stereochemistry of Steroids

Stereochemistry Steroids →The stereo chemistry of the rings markedly affects biological activity of a given clan of Steroids. There are six asymmetric carbon atoms. 5,8.9, 10, 13, 14 in the nucleus. →Therefore 64 optically active forms are Ponible. it can exist in two conformations namely Chain form and boat form. Chair conformation is more stable than boat conformation due to less angle strain →Hence all cyclohexane rings exist in chair form The hydrogen atom at (es has & configuration which is opposite from the C-19 angular methyl group B, making the A/B ring junction trans. Ring Bic and C/D trans Junction. →The configuration of 88 and 9x hydrogen and 14 a hydrogen and c-18 angular methyl group denotes trans fusion for sings B/C and C/D. →Cis and trans relationship of the four sungs may be expressed in terms of the back bone. →58 chalestane has eis. in which the A/B rings is-Syn-thans anti trans back bone are fused cis The term syn is wed in a similar fashion as anti to define a cis type relationship. Cholesterol →mol. formula - Cay H460 → optically active lx ID=390 →White crystalline solid, m.pt=149°C. occurence It occure free or as all animal cells. fatty esters in →It is first isolated from human gallstone. Main source fish liver oil, the Brain & spinal cord of cattle. Structure Elucidation determination of Determination of Carbon skeleton 1. The formula of cholesterol in C271460. • if one oxygen is replaced by two 'H' the new ned will be C27H48 hydrocarbon formed It belongs to general formula (Han-6 where. 1=27 •The general formula, preliminary indicate that cholesterol har tetracyclic carbon skeleton. 2. When cholesterol is distilled with se at 360°c well Known Diel's hydrocarbon having substituent at C-17 Pasition is formed. cholesterol over all it can be said that Cholesteral has tetracyclic e-skeleton as diel having 3 six memb ring and one 5-memb ring. It has substituent at C-17 position. Determination of functional gp 1. (n) if a compound (cholesterol) has hydroxyl gp. it can react with excess acetic anhydride in presence of Pyridine and can form ester and respective Carboxylic acid. This reaction is known as Acetylation reaction R(OH)n + n(CH₃ (0)20 PrR (OCOCH3)+ n CH3 COOH further water addition converts unused anhydride into carboxylic acid. (CH₃ CO2 + H2O2 CH3COOH if the reaction mixture is titrated with known concentration of NaOH. The retal acetic acid content can be calculated. (B) Take all the above compound except R(OH)n and titrate with NaOH, the acetic acid content due to hydrolysis of anhydride can be calculated. This test is called blank test *The difference between two carboxylic acid content (A&B Part) is the real content of carboxylic acid Produced due to acetylation of hydroxyl group in a cholesterol * Mole of carboxylic acid is equal to mate of hydroxyl group in the acetylation reaction. overall by the usual function group test It is found that cholesterol contains one hydroxyl group. 2.If a compound (cholesterol) has double bond, it can be hydrogen either by th₂ over either exponsive pt OM Cheap Raney nickel catalyst. The mole of H₂ adsorbed is equal to mole of double bond Present in the Cholesterol. + 2H Catalyst >< overall by the usual functional op test. It is found that cholesteral contain one double Bond. 16 Determination of Position of functional gp or carbon Skeleton A Position of Hydroxyl gp on chatesteral skeleton The Possible double Bond should be reduced first then the Possible hydroxyl gp is subjected to Oxidation Cholesterol + H₂ Pt Cholestant (Saturated) Information: OH gp is at secondary carbon. further, the Oxidized Product ketone is subjected to deep oxidation- Cholestanone (274460 + HNO3 1, 6 Dicarboxylic acid (without cacbon loss) Information •C=O gp should be flanked by methylene op on either side (ie-CH2-CO-CH2-) and it should be on E member ring •Information. 2° or at & member ring should be surrounded by methylene gf t'at B carbon Position) on elther side (1.e-一一一) H2 *Ring D is five member. So it can not bear ондь * Ring B and C are six member but it has not a single carben having flanked with methylene op on either side so it can not bear -он др *Only Ring A satisfies all condition al carbon Position either 2 or 3 it can bear of gh either at 204 3 Carbon Position.