updatedChapter5Notes

updatedChapter5Notes - Chapter
5
 Stereochemistry:
...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter
5
 Stereochemistry:
 Chiral
Molecules
 Isomerism:
 Constitutional
Isomers
and
Stereoisomers
 Stereoisomers
are
isomers
with
the
same
molecular
formula
and
same
connectivity
of
 atoms
but
different
arrangement
of
atoms
in
space.
 Enantiomers:
stereoisomers
whose
molecules
are
nonsuperposable
mirror
images
of
 each
other.
 Diastereomers:
stereoisomers
whose
molecules
are
not
mirror
images
of
each
other.
 Example:
cis
and
trans
double
bond
isomers‐
stereoisomers
that
are
diastereomers
 Example:
cis
and
trans
cycloalkane
isomers
 Enantiomers
and
Chiral
Molecules
 Chiral
molecule:
a
molecule
which
is
not
superposable
on
its
mirror
image.

A
chiral
 molecule
and
its
mirror
image
are
called
a
pair
of
enantiomers.

Molecules
that
are
 superposable
on
their
mirror
image
are
achiral.


 Example:
2‐butanol
is
a
chiral
molecule.

I
and
II
are
mirror
images
(figures
a
and
b)
and
 are
not
superposable
(figure
c).

They
are
enantiomers.
 Example:
2‐propanol,
in
contrast,
is
not
chiral.
 A
pair
of
enantiomers
is
always
possible
for
molecules
that
contain
a
single
tetrahedral
 atom
with
four
different
groups
attached
to
it.

Such
atoms
are
called
chirality
centers.


A
 molecule
with
more
than
one
tetrahedral
carbon
bonded
to
four
different
groups
is
not
 always
chiral.

Switching
two
groups
at
the
tetrahedral
center
leads
to
the
enantiomeric
 molecule
in
a
molecule
with
one
tetrahedral
carbon.

Any
atom
at
which
an
interchange
of
 groups
produces
a
stereoisomer
is
called
a
stereogenic
center.
 Carbons
at
a
tetrahedral
stereogenic
center
are
designated
with
an
asterisk
(*).
 Example:
2‐butanol
 The
Biological
Importance
of
Chirality
 The
binding
specificity
of
a
chiral
receptor
site
for
a
chiral
molecule
is
usually
only
 favorable
in
one
way.
 Chiral
molecules
can
exhibit
their
handedness
in
many
ways.
 Tests
for
Chirality:
Planes
of
Symmetry
 Plane
of
symmetry:
an
imaginary
plane
that
bisects
a
molecule
in
such
a
way
that
the
 two
halves
of
the
molecule
are
mirror
images
of
each
other.

A
molecule
with
a
plane
 of
symmetry
cannot
be
chiral.
 Example:
 2‐Chloropropane
(a)
has
a
plane
of
symmetry
but
2‐chlorobutane

(b)
does
not.
 Nomenclature
of
Enantiomers:
The
R,S
System
 Cahn‐Ingold‐Prelog
System
 The
four
groups
attached
to
the
stereogenic
carbon
are
assigned
priorities
from
highest
 (a)
to
lowest
(d).

Priorities
are
assigned
as
follows:
Atoms
directly
attached
to
the
 stereogenic
center
are
compared.

Atoms
with
higher
atomic
number
are
given
higher
 priority.

If
priority
cannot
be
assigned
based
on
directly
attached
atoms,
the
next
layer
 of
atoms
is
examined.
 Example:
 The
molecule
is
rotated
to
put
the
lowest
priority
group
back.

If
the
groups
descend
 in
priority
(a,b
then
c)
in
clockwise
direction
the
enantiomer
is
R.

If
the
groups
 descend
in
priority
in
counterclockwise
direction
the
enantiomer
is
S.
 Groups
with
double
or
triple
bonds
are
assigned
priorities
as
if
their
atoms
were
 duplicated
or
triplicated.
 In
Class
Problem:

Are
A
and
B
identical
or
enantiomers?
 In
Class
Problem:

Are
A
and
B
identical
or
enantiomers?
 Manipulate
B
to
see
if
it
will
become
superposable
with
A
 In
Class
Problem:

Are
A
and
B
identical
or
enantiomers?
 Manipulate
B
to
see
if
it
will
become
superposable
with
A
 Exchange
2
groups
to
try
to
convert
B
into
A.

One
exchange
of
groups
leads
to
the
 enantiomer
of
B.

Two
exchanges
of
groups
leads
back
to
B
 Properties
of
Enantiomers:
Optical
Activity
 Enantiomers
have
almost
all
identical
physical
properties
(melting
point,
boiling
point,
 density).

However,
enantiomers
rotate
the
plane
of
plane‐polarized
light
in
equal
but
 opposite
directions.
 Plane
Polarized
Light
 Oscillation
of
the
electric
field
of
ordinary
light
occurs
in
all
possible
planes
perpendicular
 to
the
direction
of
propagation.
 If
the
light
is
passed
through
a
polarizer
only
one
plane
emerges.
 The
Polarimeter
 Specific
Rotation
 An
empty
sample
tube
or
one
containing
an
achiral
molecule
will
not
rotate
the
plane‐ polarized
light.

An
optically
active
substance
(e.g.
one
pure
enantiomer
)
will
rotate
the
 plane‐polarized
light
.

The
amount
the
analyzer
needs
to
be
turned
to
permit
light
 through
is
called
the
observed
rotation
α. The
standard
value
specific
rotation
[α]
can
be
 calculated.

If
the
analyzer
is
rotated
clockwise
the
rotation
is
(+)
and
the
molecule

is
 dextrorotatory.

If
the
analyzer
is
rotated
counterclockwise
the
rotation
is
(‐)
and
the
 molecule
is
levorotatory.
 The
specific
rotation
of
the
two
pure
enantiomers
of
2‐butanol
are
equal
but
opposite
 There
is
no
straightforward
correlation
between
the
R,S
designation
of
an
enantiomer
 and
the
direction
[(+)
or
(‐)]
in
which
it
rotates
plane
polarized
light.
 Racemic
mixture:
a
1:1
mixture
of
enantiomers.

There
is
no
net
optical
rotation.

 Racemic
mixtures
are
often
designated
as
(+).
 Racemic
Forms
and
Enantiomeric
Excess
 Often
a
mixture
of
enantiomers
will
be
enriched
in
one
enantiomer.

One
can
measure
 the
enantiomeric
excess
(ee).
 Example
:
The
optical
rotation
of
a
sample
of
2‐butanol
is
+6.76o.

What
is
the
 enantiomeric
excess?
 The
Synthesis
of
Chiral
Molecules
 Most
chemical
reactions
which
produce
chiral
molecules
produce
them
in
racemic
form.
 Molecules
with
More
than
One
Stereogenic
Center
 The
maximum
number
of
stereoisomers
available
will
not
exceed
2n,
where
n
is
equal
to
 the
number
of
tetrahedral
stereogenic
centers.
 There
are
two
pairs
of
enantiomers
(1,
2)
and
(3,4).

Enantiomers
are
not
easily
separable
 so
1
and
2
cannot
be
separated
from
each
other.

Diastereomers:
stereoisomers
which
are
 not
mirror
images
of
each
other‐
for
instance
1
and
3
or
1
and
4.

Diastereomers
have
 different
physical
(and
chemical)
properties
and
can
be
separated
from
one
another.
 Meso
Compounds
 Sometimes
molecules
with
2
or
more
stereogenic
centers
will
have
less
than
the
 maximum
amount
of
stereoisomers.
 Meso
compound
are
achiral
despite
the
presence
of
stereogenic
centers.

They
are
not
 optically
active.

They
are
mirror
images
which
are
superosable.

They
have
a
plane
of
 symmetry.
 Naming
Compounds
with
More
than
One
 Stereogenic
Center
 The
molecule
is
manipulated
to
allow
assignment
of
each
stereogenic
center
separately.
 This
compound
is
(2R,
3R)‐2,3‐dibromobutane.
 Fischer
Projection
Formulas
 Fischer
projection
formulas
are
2‐dimensional
representations
of
chiral
molecules.


 Vertical
lines
represent
bonds
that
project
behind
the
plane
of
the
paper.

Horizontal
 lines
represent
bonds
that
project
out
of
the
plane
of
the
paper.
 Stereoisomerism
of
Cyclic
Compounds
 Neither
the
cis
not
trans
isomers
of
1,4‐dimethylcyclohexane
is
optically
active.

Each
 has
a
plane
of
symmetry.
 The
trans
and
cis
1,3‐dimethylcyclohexane
each
have
two
stereogenic
centers.

The
cis
 compound
has
a
plane
of
symmetry
and
is
meso.

The
trans
compound
exists
as
a
pair
of
 enantiomers.
 Relating
Configurations
through
Reactions
in
which
 No
Bonds
to
the
Stereogenic
Carbon
are
Broken
 A
reaction
which
takes
place
in
a
way
that
no
bonds
to
the
stereogenic
carbon
are
 broken
is
said
to
proceed
with
retention
of
configuration.
 Relative
configuration:
the
relationship
between
comparable
stereogenic
centers
in
 two
different
molecules.

(R)‐1‐Bromo‐2‐butanol
and
(S)‐2‐butanol
have
the
same
 relative
configuration.

Absolute
configuration:
the
actual
3‐dimensional
orientation
 of
the
atoms
in
a
chiral
molecule.

Absolute
configurations
can
be
determined
from
 x‐ray
crystallographic
analysis.
 Chiral
Molecules
that
Do
Not
Possess
a
Tetrahedral
 Atom
with
Four
Different
Groups
 Atropoisomer:
conformational
isomers
that
are
stable.
 Allenes:
contain
two
consecutive
double
bonds.
 More
on
Molecules
with
Multiple
Chiral
Centers
 Many 
 naturally 
 occurring 
 compounds 
 contain 
 several 
 chiral 
 centers. 
 By 
 an 
 analysis
 similar 
 to 
 that 
 described 
 for 
 the 
 case 
 of 
 two 
 chiral 
 centers, 
 it 
 can 
 be 
 shown 
 that 
 the
 maximum 
 number 
 of 
 stereoisomers 
 for 
 a 
 particular 
 constitution 
 is 
 2n, 
 where 
 n 
 is 
 equal
 to
the
number
of
chiral
centers.
 The
best
examples
of
substances
with
mulitple
chiral
centers
are
the
carbohydrates.
 OH OH O HO OH OH H An
aldohexose:
 4
chiral
centers
=
24,
or
 16
stereoisomers
 Steroids
are
another
class
of
natural
products
with
multiple
chiral
centers.
 H OH CH3 CO2H CH3 CH3 H HO H H OH Cholic
acid
(from
bile):
 11
chiral
centers
=
211,
or
 2048
stereoisomers
 More
Regarding
Meso
Compounds
 Fischer 
 projection 
 formulas 
 can 
 help 
 identify 
 meso 
 compounds. 
 
 They 
 allow 
 for 
 easy
 recognition 
 of 
 planes 
 of 
 symmetry. 
 
 When 
 using 
 Fischer 
 projections 
 for 
 this 
 purpose,
 however,
be
sure
to
remember
what
three‐dimensional
objects
they
stand
for.
 CH3 HO H CH3 H OH H HO CH3 CH3 OH H H H CH3 CH3 OH OH Of
the
three
stereoisomeric
2,3‐butanediols,
 notice
that
only
in
the
meso
stereoisomer
 does
does
there
exist
a
mirror
plane.
 (2R,3R) (2S,3S) meso For
cyclic
compounds
with
multiple
stereocenters,
look
for
any
planes
of
symmetry.

 For 
 the 
 1,2‐dibromocyclopropanes, 
 the 
 cis 
 diastereomer 
 has 
 a 
 plane 
 of 
 symmetry 
 and
 thus
is
a
meso
form.
 H Br Br H H H R Br R H S H S Br R Br S Br (1R,2R)-dibromocyclopropane (1S,2S)-dibromocyclopropane cis-1,2-dibromocyclopropane In
class
problem:
Draw
all
possible
stereoisomers
of
2,3,4‐pentanetriol.
How
many
 stereocenters
are
there?
Identify
the
R
and
S
configurations
for
each
stereocenter.
 Identify
which
compounds
are
enantiomers,
diastereomers,
and
meso.

 Molecules
with
Chiral
Centers
Other
than
Carbon
 Atoms 
 other 
 than 
 carbon 
 may 
 also 
 be 
 chiral 
 centers. 
 
 Any 
 tetrahedral 
 atom 
 with 
 four
 different 
 groups 
 attached 
 to 
 it 
 is 
 a 
 chiral 
 center. 
 
 Silicon, 
 like 
 carbon, 
 has 
 a 
 tetrahedral
 arrangement
of
bonds
when
it
bears
four
substituents.

A
large
number
of
organosilicon,
 organogermanium
and
organonitrogen
compounds
in
which
the
central
atom
bears
four
 different
groups
have
been
resolved
into
their
enantiomers.

 R4 Si R1 R4 Ge R1 R4 N R1 R2 R1 S X R3 R2 O R3 R2 R3 R2 Sulfoxides, 
 like 
 certain 
 examples 
 of 
 other 
 functional 
 groups 
 where 
 one 
 of 
 the 
 four
 groups
is
a
nonbonding
electron
pair,
are
also
chiral.

This
is
not
the
case
for
amines
due
 to
rapid
pyramidal
inversion.
 b very fast a b N a c N c Other
Chirality
Terms:
Rotation
of
Polarized
Light
 Rotation
of
the
plane
of
polarized
light
in
the
clockwise
direction
is
taken
as
positive
(+),
 and
rotation
in
the
counterclockwise
sense
is
taken
as
negative
(‐)
rotation.

Older
terms
 for 
 positive 
 and 
 negative 
 rotations 
 were 
 dextrorotatory 
 (to 
 the 
 right) 
 and 
 levorotatory
 (to 
 the 
 left). 
 At 
 one 
 time, 
 the 
 symbols 
 d 
 and 
 l 
 were 
 used 
 to 
 distinguish 
 between
 enantiomeric 
 forms 
 of 
 a 
 substance. 
 Configurations 
 of 
 chiral 
 molecules 
 were 
 related 
 to
 each 
 other 
 through 
 reaction 
 of 
 known 
 stereochemistry. 
 The 
 L 
 and 
 D 
 convention 
 for
 amino 
 acid 
 configuration 
 refers 
 not 
 to 
 the 
 optical 
 activity 
 of 
 the 
 amino 
 acid 
 itself, 
 but
 rather 
 to 
 the 
 optical 
 activity 
 of 
 the 
 isomer 
 of 
 glyceraldehyde 
 from 
 which 
 it 
 can
 theoretically 
 be 
 synthesized 
 (D‐glyceraldehyde 
 is 
 dextrorotatory; 
 L‐glyceraldehyde 
 is
 levorotatory).
 OH HO O N H H O H OH (S)-Glyceraldehyde or L-glyceraldehyde L-Proline or (S)-proline Other
Chirality
Terms:
Fischer
Projections
 Organic 
 chemists 
 often 
 use 
 an 
 informal 
 nomenclature 
 system 
 based 
 on 
 Fischer
 projections 
 to 
 distinguish 
 between 
 diastereomers. 
 
 When 
 the 
 carbon 
 chain 
 is 
 vertical
 and 
 like 
 substituents 
 are 
 on 
 the 
 same 
 side 
 of 
 the 
 Fischer 
 projection, 
 the 
 molecule 
 is
 described 
 as 
 the 
 erythro 
 diastereomer. 
 When 
 like 
 substituents 
 are 
 on 
 opposite 
 sides 
 of
 the
Fischer
projection,
the
molecule
is
described
as
the
threo
diastereomer.
 For 
 the 
 2,3‐dihydroxybutanoic 
 acids, 
 compounds 
 I 
 and 
 II 
 are 
 erythro 
 stereoisomers
 and
III
and
IV
are
threo.
 CO2H H H CH3 OH OH HO HO CH3 CO2H H H H HO CH3 CO2H OH H HO H CH3 CO2H H OH I erythro II erythro III threo IV threo Separation
of
Enantiomers:
Resolution
 Enantiomers 
 have 
 identical 
 solubilities 
 in 
 ordinary 
 solvents, 
 and 
 they 
 have 
 identical
 boiling 
 or 
 melting 
 points. 
 
 Consequently, 
 the 
 conventional 
 methods 
 for 
 separating
 organic 
 compounds, 
 such 
 as 
 recrystallization 
 and 
 distillation, 
 fail 
 when 
 applied 
 to 
 a
 racemic
mixture.

The
separation
of
a
racemic
mixture
into
its
enantiomeric
components
 is
termed
resolution.
 
The
first
resolution, 
that
of
tartaric
acid,
was
carried
out 
by
Louis
 Pasteur
in
1848.


 CO2H H HO CO2H OH H (2R,3R)-Tartaric acid Pasteur
noticed
that
the
sodium
ammonium
salt
of
optically
inactive
 tartaric
acid

was
a
mixture
of
two‐mirror
image
crystal
forms.

With
 microscope
and
tweezers,
Pasteur
separated
the
two.
 Separation
of
Enantiomers:
Resolution
 One 
 of 
 the 
 most 
 useful 
 procedures 
 for 
 separating 
 enantiomers 
 is 
 based 
 on 
 allowing 
 a
 racemic
mixture
to
react
with
a
single
enantiomer
of
some
other
compound
(a
resolving
 agent). 
 
 This 
 changes 
 a 
 racemic 
 form 
 into 
 a 
 mixture 
 of 
 diastereomers. 
 
 Diastereomers,
 because 
 they 
 have 
 different 
 melting 
 points, 
 boiling 
 points, 
 and 
 different 
 solubilities,
 can
be
separated
by
conventional
means.
 Types
of
Resolution
 Whenever 
 possible, 
 the 
 chemical 
 reactions 
 involved 
 in 
 the 
 formation 
 of 
 diastereomers
 and 
 their 
 conversion 
 to 
 separate 
 enantiomers 
 are 
 simple 
 acid‐base 
 reactions. 
 For
 example, 
 naturally‐occurring 
 (S)‐(‐)‐malic 
 acid 
 is 
 often 
 used 
 to 
 resolve 
 amines. 
 
 Amines
 are
bases
and
are
protonated
by
malic
acid
to
give
a
mixture
of
diastereomeric
salts.
 OH NH2 HO2C CO2H NH3 O2C OH CO2H 1-Phenylethylamine (racemic mixture) (S)-(-)-Maiic acid (resolving agent) 1-Phenylethylammonioum (S)-malate (mixture of diastereomeric salts) Another
approach,
called
kinetic
resolution,
depends
on
the
different
rates
of
reaction
 of 
 two 
 enantiomers 
 with 
 a 
 chiral 
 reagent. 
 
 A 
 very 
 effective 
 form 
 of 
 kinetic 
 resolution
 uses 
 enzymes 
 as 
 chiral 
 catalysts 
 to 
 selectively 
 bring 
 about 
 the 
 reaction 
 of 
 one
 enantiomer
in
a
racemic
mixture.
 
This
is
known
as
enzymatic
resolution.
 
Lipases,
or
 esterases, 
 enzymes 
 that 
 catalyze 
 ester 
 hydrolysis, 
 are 
 often 
 used. 
 
 The 
 growing
 interest 
 in 
 chiral 
 drugs 
 has 
 stimulated 
 the 
 development 
 of 
 large 
 scale 
 enzymatic
 resolution
as
a
commercial
process.
 O OE t F lipase H2O F O OE t F O OH EtOH Chiral
Drugs
 The 
 U.S. 
 Food 
 and 
 Drug 
 Administration 
 and 
 the 
 pharmaceutical 
 industry 
 are 
 very
 interested 
 in 
 the 
 production 
 of 
 chiral 
 drugs, 
 that 
 is, 
 drugs 
 that 
 contain 
 a 
 single
 enantiomer 
 than 
 a 
 racemate. 
 
 The 
 antihypertensive 
 drug 
 methyldopa 
 (Aldomet), 
 for
 example,
owes
its
effect
excuslively
to
the
(S)‐enantiomer.
 
In
the
case
of
penicillamine,
 the 
 (S) 
 enantiomer 
 is 
 a 
 highly 
 potent 
 therapeutic 
 for 
 arthritis, 
 while 
 the 
 (R) 
 isomer 
 has
 no
therapeutic
action
and
is
highly
toxic.
 
The
anti‐inflammatory
agent
ibuprofen
(Advil,
 Motrin, 
 Naproxen) 
 is 
 marketed 
 as 
 a 
 racemate 
 even 
 though 
 only 
 the 
 (S) 
 enantiomer 
 is
 the 
 active 
 agent. 
 
 The 
 (R) 
 isomer 
 has 
 no 
 therapeutic 
 action 
 and 
 is 
 slowly 
 converted 
 to
 the
(S)
enantiomer
in
the
body.
 H2N CH3 CO2H HO OH Methyldopa HS H3C NH2 CO2H CH3 H3C Ibuprofen CH3 CH3 CO2H Penicillamine Until 
 recently, 
 chiral 
 substances 
 were, 
 with 
 few 
 exceptions, 
 prepared, 
 sold, 
 and
 administered 
 as 
 racemic 
 mixtures 
 even 
 though 
 the 
 desired 
 therapeutic 
 activity
 resided 
 in 
 only 
 one 
 enantiomer. 
 
 Spurred 
 by 
 a 
 number 
 of 
 factors 
 ranging 
 from 
 safety
 to 
 economics, 
 this 
 practice 
 is 
 changing 
 as 
 more 
 and 
 more 
 chiral 
 synthetic 
 drugs
 become
available
in
enantiomerically
pure
form.
 Thalidomide
 A
much
more
serious
drawback
to
using
chiral
drugs
as
racemic
mixtures
is
illustrated
by
 thalidomide, 
 briefly 
 employed 
 as 
 a 
 sedative 
 and 
 antinausea 
 drug 
 in 
 Europe 
 from
 1959‐1962.

Thalidomide
was
chiefly
sold
and
prescribed
to
pregnant
women
to
combat
 morning 
 sickness 
 and 
 aid 
 in 
 sleeping. 
 
 These 
 desired 
 properties 
 are 
 directly 
 associated
 with
the
(R)
enantiomer.
 (S)‐Thalidomide, 
 however, 
 is 
 a 
 teratogen 
 and 
 causes 
 birth
 defects.
 
From
1956
to
1962,
about 
10,000
children
in 
Africa
 and 
 Europe 
 were 
 born 
 with 
 severe 
 malformities, 
 because
 their
mothers
had
taken
thalidomide
during
pregnancy.

Even
 if
a
person
is
given
the
pure
(R)
enantiomer,
the
enantiomers
 can 
 interconvert 
 in 
 vivo. 
 Thus, 
 giving 
 the 
 single 
 enantiomer
 will
not
prevent
the
teratogenic
effects.

 O N NH O O O Thalidomide Today, 
 thalidomide 
 has 
 been 
 FDA‐approved 
 for 
 treatment 
 of 
 a 
 variety 
 of 
 ailments,
 including 
 multiple 
 myeloma 
 (cancer 
 of 
 plasma 
 cells), 
 AIDS 
 and 
 erythema 
 nodosum
 leprosum
(a
skin
condition
associated
with
leprosy),
but
is
not
prescribed
for
pregnant
 women.
 Chirality
and
Pharmaceutical
Industry
 Basic
research
aimed
at
controlling
the
stereochemistry
of
chemical
reactions
has
led
to
 novel 
 methods 
 for 
 the 
 synthesis 
 of 
 chiral 
 molecules 
 in 
 enantiomerically 
 pure 
 form.

 Aspects 
 of 
 this 
 work 
 were 
 recognized 
 with 
 the 
 award 
 of 
 the 
 2001 
 Nobel 
 Prize 
 in
 Chemistry 
 to 
 William 
 S. 
 Knowles 
 (Monsanto), 
 Ryoji 
 Noyori 
 (Nagoya 
 University), 
 and 
 K.
 Barry 
 Sharpless 
 (Scripps 
 Research 
 Insititute). 
 The 
 researchers 
 each 
 developed 
 protocols
 in
which
chiral
catalysts
react
with
achiral
starting
materials
to
give
chiral
products.
This
 is
termed
asymmetric
catalysis.


 CH2 H3C H CO2H H2 (S)-BINAP-Ru(OC(O)CH3)2 MeOH CO2H MeO MeO (S)-Naproxen (an anti-inflammatory) 92% yield, 97% enatiomeric excess (ee) One 
 incentive 
 to 
 developing 
 enantiomerically 
 pure 
 versions 
 of 
 existing 
 drugs 
 is 
 that
 the 
 novel 
 production 
 methods 
 they 
 require 
 may 
 make 
 them 
 eligible 
 for 
 patent
 protection 
 separate 
 from 
 that 
 of 
 the 
 original 
 drugs. 
 
 Thus 
 the 
 temporary 
 monopoly
 position
that
patent
law
views
as
essential
to
fostering
innovation
can
be
extended
by
 transforming 
 a 
 successful 
 chiral, 
 but 
 racemic, 
 drug 
 into 
 an 
 enantiomerically 
 pure
 version.
 ...
View Full Document

This note was uploaded on 06/19/2009 for the course CHEM 2311 taught by Professor Tyson during the Fall '07 term at Georgia Tech.

Ask a homework question - tutors are online