Lesson 2

BIO-ORGANIC CHEMISTRY

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Objectives:

1. Define isomerism.

2. Distinguish the different types of isomers present in carbon chains.

3. Draw structural formulas of various isomers.

4. Define chirality and optical activity.

Lesson 2

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ISOMERISMDEFINE ISOMERS

Isomers refer to two or more molecules that have the same empirical formula but the individual atoms are connected in different ways, leading to different moleculesdifferent molecules.

ISOMERS

Constitutional IsomersStereoisomers

Enantiomers (mirror-image)

Diastereomers (non-mirror-image)

Configurational diastereomers

cis - trans diastereomers

Lesson 2

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ISOMERISMCONSTITUTIONAL ISOMER

It has different connections among atoms.

Skeletal – different carbon skeletonSkeletal – different carbon skeleton

n- PENTANE ISOPENTANE

Functional – different functional groupsFunctional – different functional groups

CH3CH2OH CH3OCH3

alcohol ether

Lesson 2

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ISOMERISMCONSTITUTIONAL ISOMER

It has different connections among atoms.

Positional- different position of functional Positional- different position of functional groupsgroups

ISOPROPYLAMINE PROPYLAMINE

CH3

CH CH3

NH2

CH3

CH2

CH2

NH2

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ISOMERISMSTEREOISOMERS

It involves same connections among atoms but different geometry.

Enantiomers- non-superimposable mirror – image.Enantiomers- non-superimposable mirror – image.

Lesson 2

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ISOMERISMSTEREOISOMER

It has same connections among atoms but different geometry.

Diastereomers- non-superimposable non-mirror – image.Diastereomers- non-superimposable non-mirror – image.

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ISOMERISMSTEREOISOMERS

It involves same connections among atoms but different geometry.

Cis-trans: substituents on same side or opposite side of Cis-trans: substituents on same side or opposite side of ring or double bond. ring or double bond.

http://www.uwplatt.edu/~sundin/354-7/l547-08.htm#CYCLO

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CHIRALITY (ky-ral; Greek cheir; meaning “hand”)

It is when molecules are optically active…It is when molecules are optically active…

http://www.novactabio.com/biotrans.php

Chiral image from Amino Acid Dating at http://www.creation-science-prophecy.com/amino/

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Chemistry connection

Chiral DrugsChiral DrugsJust as various stereoisomeric forms of a chiral molecule have different physical

properties, these stereoisomers manifests different biological properties. More dramatic examples of how a change in isomerisms can affect the biological properties of molecules

are found in drugs . A more commonly prescribed medicine, Prozac where the racemic fluoxetine is extraordinarily effective as antidepressant but it has no activity against

migraine. While the pure S- enantiomer however works remarkably well in preventing migrane.

Drugs that come from natural sources, either directly or after chemical modification, are usually chiral and are generally found as a single enantiomer rather then the racemic

mixture. Penicillin V, is an antibiotic isolated from Penicillium mold. This drug has a 2S, 5R, 6R configuration.

To become biologically active, chiral molecules must fit into a chiral receptor at the target site, similar to hands fitting into gloves. Just as left hand can fit only into a left-hand glove,

so as a particular stereoisomer can fit only into a receptor with proper complementary shape. SOURCE: Adapted from Fundamentals of SOURCE: Adapted from Fundamentals of

Organic Chemistry by J. McMurry, 5Organic Chemistry by J. McMurry, 5 thth ed., ed., 20032003

(S)-FluoxetinePenicillin V