美国药典旋光度

781

OPTICAL

ROTATION

旋光

Many

pharmaceutical

substances

are

optically

active

in

the

sense

that

they

rotate

a

n

incident

plane

of

polarized

light

so

that

the

transmitted

light

emerges

at

a

measu

rable

angle

to

the

plane

of

the

incident

light.

This

property

is

characteristic

of

som

e

crystals

and

of

many

pharmaceutical

liquids

or

solutions

of

solids.

Where

the

pro

perty

is

possessed

by

a

liquid

or

by

a

solute

in

solution,

it

is

generally

the

result

o

f

the

presence

of

one

or

more

asymmetric

centers,

usually

a

carbon

atom

with

fou

r

different

substituents.

The

number

of

optical

isomers

is

2n,

where

n

is

the

numbe

r

of

asymmetric

centers.

Polarimetry,

the

measurement

of

optical

rotation,

of

a

phar

maceutical

article

may

be

the

only

convenient

means

for

distinguishing

optically

acti

ve

isomers

from

each

other

and

thus

is

an

important

criterion

of

identity

and

purity.

很多药用物质具有光学活性，

他们能够使入射的平面偏振光旋转，

这样射出的光线与入射光

< br>线的角度形成可测量的角度。

这个性质是一些结晶状物体或者药用液体或固体的溶 液所具有

的特性。

在某种液体或者溶液中的溶质具有该性质的情 况下，

这通常是存在着一个或者多个

不对称中心的结果，经常是 一个碳原子与四个不同的取代基。光学异构体的数量是

2

n< /p>

，在

此

n

是不对 称中心的数量。药用物质的旋光测定法，即测定光学旋转的方法，也许是用于

区分具有光 学活性的异构体的方法中唯一简便的方法。

因此，

该方法是鉴别 和纯度的一个重

要标准。

Substances

that

may

show

optical

rotatory

power

are

chiral.

Those

that

rotate

light

in

a

clockwise

direction

as

viewed

towards

the

light

source

are

dextrorotatory,

or

(+)

optical

isomers.

Those

that

rotate

light

in

the

opposite

direction

are

called

levor

otatory

or

(

–

)

optical

isomers.

(The

symbols

d-

and

l-,

formerly

used

to

indicate

de

xtro-

and

levorotatory

isomers,

are

no

longer

sanctioned

owing

to

confusion

with

D-

and

L-,

which

refer

to

configuration

relative

to

D-glyceraldehyde.

The

symbols

R

a

nd

S

and

and

are

also

used

to

indicate

configuration,

the

arrangement

of

atoms

or

groups

of

atoms

in

space.)

能够表现出旋光能力的物质是手性的。

那些朝向光源观察时按顺时针方向旋转光线的物质是

右旋性的或者

(+)

光学异构体。（其符号

d-

和

l-

，原 先是用来表示右旋的和左旋的异构体，

现在由于容易与

D-

和

L-

混淆而不再使用，这两个符号涉及与

D-

甘油醛相关的结构）。符号

R

和

S

以及

和

也都是用于表示结构、原子或原子组在空间中的排列。

The

physicochemical

properties

of

nonsuperimposable

chiral

substances

rotating

pla

ne

polarized

light

in

opposite

directions

to

the

same

extent,

enantiomers,

are

identi

cal,

except

for

this

property

and

in

their

reactions

with

other

chiral

substances.

Ena

ntiomers

often

exhibit

profound

differences

in

pharmacology

and

toxicology,

owing

t

o

the

fact

that

biological

receptors

and

enzymes

themselves

are

chiral.

Many

article

s

from

natural

sources,

such

as

amino

acids,

proteins,

alkaloids,

antibiotics,

glycosi

des,

and

sugars,

exist

as

chiral

compounds.

Synthesis

of

such

compounds

from

no

nchiral

materials

results

in

equal

numbers

of

the

enantiomers,

racemates.

Racemat

es

have

a

net

null

optical

rotation,

and

their

physical

properties

may

differ

from

tho

se

of

the

component

enantiomers.

Use

of

stereoselective

or

stereospecific

synthetic

methods

or

separation

of

racemic

mixtures

can

be

used

to

obtain

individual

optical

isomers.

具有在相反方向旋转平面偏振光到同样程度的理化特性的不可重叠手性物质，即对映结构

体，

除了上述特性以及与其他手性物质进行的反应的区别之外，

是完全相同的。

由于生物受

体和酶自身 均是手性的，

对映异构体经常在药理与毒理方面展现出深刻的差异。

许多天然来

源的物品，例如氨基酸、蛋白质、生物碱、抗生素、糖苷、蔗糖等，以手 性化合物的形式存

在。

使用非手性物料合成此类化合物导致等量 的对映异构体和外消旋物。

外消旋物有净无效

旋光（