Drugs from Natural ProductsPlant Sources - ACS Publications

1 Drugs from Natural Products—Plant Sources S. MORRIS K U P C H A N University of Virginia, Charlottesville, V a . 22901 The plant kingdom

Downloaded by NEW YORK UNIV on May 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0108.ch001

of useful drugs.

has served as one of man's oldest

The history

inals, such as morphine

of classic

and quinine,

illustrates

the older medicinals

as major and relatively

constituents

remedies.

of

folk

agents, such as reserpine minor constituents guided

by

assay.

for plant

isolation

and characterization and

derived

jatrophone.

fascinating

number

array of novel biologically

for

is illustrated

been was future

by

inhibitors

of many

guided by biological

have

model

of the tumor

Screening

isolated discovered

whose isolation A

medicinals

crude extracts yielded a significant and fractionations

easily

recently

mixtures,

pharmacological

searches nolepin

More

medic-

the origin of

and vincaleukoblastine,

of complex

sources

plant-derived

the ver-

hundreds

of active

of

extracts,

assays have yielded active

plant

a

products.

^T^he use i n m e d i c i n e of d r u g s d e r i v e d f r o m plants goes b a c k to a n t i q u i t y . Α

W h e n one considers the t h e r a p e u t i c

i m p a c t of m o r p h i n e , q u i n i n e ,

d i g i t a l i s , ergot, atropine, cocaine, reserpine, a n d v i n c a l e u k o b l a s t i n e , to n a m e b u t a f e w , it is e v i d e n t h o w great is the d e b t of m e d i c i n e to p l a n t d e r i v e d drugs even today.

I f one adds the synthetic d e r i v a t i v e s a n d

variants of p l a n t - d e r i v e d p r o d u c t s , the role of n a t u r a l p r o d u c t s f r o m p l a n t sources has b e e n most i m p r e s s i v e . T h e most i m p o r t a n t p l a n t - d e r i v e d d r u g s w e r e d e v e l o p e d

between

1800 a n d 1950. T h e past f e w decades h a v e w i t n e s s e d a n u n q u e s t i o n a b l e d i m i n u t i o n i n t h e n u m b e r of s u c h c o m p o u n d s i n t r o d u c e d i n t o m e d i c i n e . T h e s e facts have l e d to suggestions that the intensive investigations of the past c e n t u r y h a v e n e a r l y exhausted the p l a n t k i n g d o m as a p o t e n t i a l source f o r n e w d r u g s a n d that f u t u r e w o r k i n this area is u n l i k e l y to b e rewarding.

I address m y s e l f to the c o n t r a r y thesis—viz., that the p l a n t

k i n g d o m continues to offer a r i c h a n d v i r t u a l l y i n e x h a u s t i b l e s u p p l y of new

potential

drugs.

H o w e v e r , the success

i n t a p p i n g this

source

w i l l d e p e n d u p o n the extent to w h i c h n e w e r approaches to the s t u d y of b i o l o g i c a l l y - a c t i v e p l a n t constituents are u s e d . 1

In Drug Discovery; Bloom, B., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

DRUG

DISCOVERY

The Fast: Morphine and Quinine A s w e l o o k to the past, m o r p h i n e a n d q u i n i n e represent classic exa m p l e s of early p l a n t - d e r i v e d m e d i c i n a l s . O p i u m , the s u n - d r i e d latex of the u n r i p e f r u i t of Papaver

somniferum,

before history was recorded.

is b e l i e v e d to h a v e b e e n u s e d

T h e first u n d i s p u t e d reference to p o p p y

j u i c e is f o u n d i n the w r i t i n g s o f T h e o p h r a s t u s i n the t h i r d c e n t u r y B . C . D i o s c o r i d e s i n the first c e n t u r y A . D . w a s f u l l y a c q u a i n t e d w i t h t h e m e t h o d f o r c o l l e c t i n g a n d p r e p a r i n g o p i u m , a n d his d i r e c t i o n s f o r p r e p a r i n g s y r u p of p o p p y are essentially u n c h a n g e d i n m o d e r n p h a r m a c o p e i a s .

Arabian


p h y s i c i a n s w e r e w e l l v e r s e d i n t h e uses of o p i u m . T h i s d r u g w a s i n t r o d u c e d to the O r i e n t a n d C h i n a b y A r a b i a n traders.

T h e s p r e a d of the

o p i u m h a b i t t h r o u g h o u t C h i n a d i d n o t o c c u r u n t i l t h e latter p a r t of t h e e i g h t e e n t h c e n t u r y w h e n the P o r t u g u e s e a n d later t h e E n g l i s h started to e x p l o i t the natives i n this r e g a r d . T h e w a r against o p i u m has c o n t i n u e d i n the O r i e n t a n d elsewhere ever since.

Figure 1.

Morphine

F r o m the sixteenth c e n t u r y a n d w e l l i n t o the n i n e t e e n t h c e n t u r y t h e uses of o p i u m f o r its analgesic a n d h y p n o t i c properties w e r e f a i r l y w e l l u n d e r s t o o d i n E u r o p e . I n 1805 a y o u n g G e r m a n p h a r m a c i s t i n H a n o v e r n a m e d Serturner i s o l a t e d a n d d e s c r i b e d m o r p h i n e . T h i s e p o c h a l

finding

w e n t u n n o t i c e d u n t i l his later p u b l i c a t i o n i n 1816. Serturner almost lost his l i f e b y e x p e r i m e n t i n g w i t h m o r p h i n e o n himself.

T h e d i s c o v e r y of

other a l k a l o i d s i n o p i u m q u i c k l y f o l l o w e d that of m o r p h i n e , a n d t h e use of p u r e a l k a l o i d s rather t h a n c r u d e p r e p a r a t i o n s soon s p r e a d t h r o u g h o u t the m e d i c a l w o r l d . E x t e n s i v e s t r u c t u r a l studies l e d to e l u c i d a t i o n of m o r phine's structure b y G u l l a n d a n d R o b i n s o n i n 1925 ( I ) , a n d t o t a l s y n theses b y Gates a n d T s c h u d i ( 2 ) a n d b y E l a d a n d G i n s b u r g ( 3 ) firmed

c o m p l e t e l y the structure

a n d stereochemistry

con-

of the m o l e c u l e

( F i g u r e 1 ). It is n o t e w o r t h y that m o r p h i n e is the m a j o r a l k a l o i d of o p i u m ; i n a g o o d g r a d e of o p i u m i t averages 1 0 % , a l t h o u g h samples c o n t a i n i n g over 2 0 % h a v e b e e n r e p o r t e d . Q u i n i n e is the chief a l k a l o i d of c i n c h o n a , t h e b a r k of the c i n c h o n a tree i n d i g e n o u s to c e r t a i n regions of S o u t h A m e r i c a . T h e first w r i t t e n


1.

κυρ C H A N

Fiant

3

Sources

r e c o r d of the use of c i n c h o n a occurs i n a r e l i g i o u s b o o k w r i t t e n i n 1633 a n d p u b l i s h e d i n S p a i n i n 1639.

A v a r i e t y of c o l o r f u l a n d f a n c i f u l v e r

sions of the d i s c o v e r y of the fever b a r k exist.

A p o p u l a r a n d persistent

v e r s i o n is that the b a r k w a s u s e d i n 1638 to treat C o u n t e s s A n n a d e l C h i n c h o n , w i f e of the v i c e r o y to P e r u , a n d that her m i r a c u l o u s c u r e re s u l t e d i n the i n t r o d u c t i o n of c i n c h o n a i n t o S p a i n i n 1639 f o r the treatment of ague.

B y 1640, the d r u g w a s b e i n g u s e d f o r fevers i n E u r o p e .

The

t e r m " c i n c h o n a " w a s chosen b y L i n n é ( w h o a c c i d e n t a l l y m i s s p e l l e d i t ) f o r t h e species of plants y i e l d i n g the d r u g . Jesuit priests w e r e the m a i n i m porters a n d d i s t r i b u t o r s of c i n c h o n a i n E u r o p e , a n d the n a m e "Jesuit b a r k " Downloaded by NEW YORK UNIV on May 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0108.ch001

soon b e c a m e a t t a c h e d to the d r u g . F o r almost t w o centuries, the b a r k w a s u s e d i n m e d i c i n e as a p o w d e r , extract, or i n f u s i o n . I n 1820 P e l l e t i e r a n d C a v e n t o u i s o l a t e d q u i n i n e a n d c i n c h o n i n e f r o m c i n c h o n a , a n d the use of the a l k a l o i d s as s u c h g a i n e d f a v o r r a p i d l y . E x t e n s i v e a n d classic studies l e d to e l u c i d a t i o n o f

the

structure of q u i n i n e ( F i g u r e 2 ) (4)

(5).

a n d to its t o t a l synthesis i n 1944

C i n c h o n a contains 25 closely r e l a t e d a l k a l o i d s , of w h i c h the most i m p o r tant are q u i n i n e , q u i n i d i n e , c i n c h o n i n e , a n d c i n c h o n i d i n e . T h e

average

y i e l d of a l k a l o i d is a b o u t 6 - 7 % , of w h i c h one-half to t w o - t h i r d s is q u i n i n e . It has b e e n s a i d that q u i n i n e owes its d o m i n a n t p o s i t i o n i n the treatment of m a l a r i a o n l y to the fact that it was the first a l k a l o i d i s o l a t e d f r o m c i n c h o n a , a n d that there is little a m o n g the f o u r major a l k a l o i d s to choose f r o m i n t r e a t i n g this disease

(6).

Figure 2.

Quinine

T h e h i s t o r y of m o r p h i n e a n d q u i n i n e , l i k e that of most classic p l a n t d e r i v e d m e d i c i n a l s , reveals that the c o m p o u n d s r e p r e s e n t e d major r e l a t i v e l y easily i s o l a t e d p l a n t constituents.

and

T h e r e a d y a c c e s s i b i l i t y of the

c o m p o u n d s p l a y e d a major r o l e i n their c h a r a c t e r i z a t i o n as the p r i n c i p l e s of the plants.


active

4

DRUG

DISCOVERY

The Present: Reserpine and Vincaleukoblastine R e s e r p i n e a n d v i n c a l e u k o b l a s t i n e represent the most i m p o r t a n t p l a n t d e r i v e d m e d i c i n a l s i n t r o d u c e d i n t o m e d i c i n e b y o u r g e n e r a t i o n , a n d i t is i n s t r u c t i v e to c o m p a r e t h e i r h i s t o r y w i t h those of m o r p h i n e a n d q u i n i n e . D e s c r i p t i o n s of the use of extracts of plants r e s e m b l i n g Rauwolfia

may

b e t r a c e d b a c k to a n c i e n t H i n d u a y u r v e d i c w r i t i n g s . T h e y w e r e u s e d i n p r i m i t i v e H i n d u m e d i c i n e f o r a v a r i e t y of diseases, i n c l u d i n g snake b i t e , h y p e r t e n s i o n , i n s o m n i a , a n d i n s a n i t y . T h e early remedies w e r e u s e d f o r v a r i o u s other purposes, b u t i t seems clear n o w that o u r present


a p p l i c a t i o n of Rauwolfia

day

alkaloids i n treating hypertension a n d mental

disease w a s f o r e s h a d o w e d i n the f o l k m e d i c i n e of the E a s t e r n

peoples.

OMe Figure 3. A l t h o u g h Rauwolfia

Reserpine

w a s i n v e s t i g a t e d i n the n i n e t e e n t h c e n t u r y a n d

the presence of a l k a l o i d s i n d i c a t e d , a systematic i n v e s t i g a t i o n of w a s o n l y started b y S i d d i q u i a n d S i d d i q u i i n 1931

(7).

Rauwolfia

F i v e alkaloids

w e r e i s o l a t e d at that t i m e , a n d despite the f a c t that one a l k a l o i d (serp e n t i n e ) h a d a b l o o d - p r e s s u r e r e d u c i n g effect, n o n e of the five s h o w e d the characteristics w h i c h w e r e later c a l l e d " r e s e r p i n e l i k e " (8).

Chopra

a n d others c o n c l u d e d that a d d i t i o n a l p h a r m a c o l o g i c a l l y a c t i v e m a t e r i a l m u s t b e present i n the w h o l e root f o r w h i c h the c r y s t a l l i n e a l k a l o i d s a v a i l a b l e at the t i m e c o u l d not a c c o u n t (9, 10).

T h e Rauwolfia

problem

r e c e i v e d a great s t i m u l u s f r o m the 1949 p a p e r b y V a k i l i n the Heart Journal o n the a n t i h y p e r t e n s i v e effects of Rauwolfia (II).

British

extracts i n m a n

I n the n e w e r studies, systematic f r a c t i o n a t i o n a n d i s o l a t i o n w e r e

c o u p l e d w i t h p h a r m a c o l o g i c a l e v a l u a t i o n , a n d it b e c a m e a p p a r e n t

that

the h y p o t e n s i v e a n d a l k a l o i d a l m a t e r i a l w a s c o n c e n t r a t e d into the "oleoresin" fraction.

R e s e r p i n e , the most i m p o r t a n t Rauwolfia

alkaloid, was

i s o l a t e d f r o m the " o l e o r e s i n " f r a c t i o n i n 1952 ( 1 2 ) , a n d s h o r t l y a f t e r w a r d it w a s s h o w n to b e responsible f o r most of the t r a n q u i l i z i n g a n d h y p o tensive effects of Rauwolfia ( F i g u r e 3 ) (13)

extracts.

T h e e l u c i d a t i o n of its

a n d a n elegant t o t a l synthesis (14,15)

structure

constituted major


1.

K U P C H A N

5

Fiant Sources

a c h i e v e m e n t s i n a l k a l o i d c h e m i s t r y . R e s e r p i n e is o n e of o v e r 5 0 a l k a l o i d s i s o l a t e d f r o m v a r i o u s Rauwolfia

species.

T h e b e n e f i c i a l properties o f t h e p e r i w i n k l e p l a n t , Vinca

rosea L i n n . ,

h a v e b e e n d e s c r i b e d i n m e d i c i n a l f o l k l o r e f o r m a n y years i n v a r i o u s parts of the w o r l d . A n a l l e g e d a c t i v i t y as a n o r a l h y p o g l y c e m i c agent p r o m p t e d its p h y t o c h e m i c a l e x a m i n a t i o n i n t w o different laboratories i n d e p e n d e n t l y . W h i l e n e i t h e r g r o u p c o u l d substantiate

this r e p o r t e d a c t i v i t y i n either

normal or experimentally-induced hyperglycemic rabbits, the C a n a d i a n g r o u p of N o b l e , B e e r , a n d C u t t s o b s e r v e d a p e r i p h e r a l g r a n u l o c y t o p e n i a a n d b o n e m a r r o w d e p r e s s i o n i n rats associated Downloaded by NEW YORK UNIV on May 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0108.ch001

(16).

w i t h certain

fractions

T h e s e effects g u i d e d t h e e x t r a c t i o n a n d p u r i f i c a t i o n of a n active

alkaloid, termed vincaleukoblastine.

T h e L i l l y group, w h i c h included

J o h n s o n , S v o b o d a , a n d others, d e m o n s t r a t e d that c e r t a i n a l k a l o i d a l f r a c tions i n h i b i t e d t h e g r o w t h o f a n acute l y m p h o c y t i c l e u k e m i a i n m i c e . F r a c t i o n a t i o n , f o l l o w e d b y assay i n t h e l e u k e m i c m i c e , y i e l d e d v i n c a l e u k o b l a s t i n e , v i n c r i s t i n e , a n d t w o other active d i m e r i c a l k a l o i d s (17, V i n c a l e u k o b l a s t i n e a n d v i n c r i s t i n e are n o w a m o n g t h e most

18).

important

drugs f o r t h e treatment of acute l e u k e m i a of c h i l d h o o d a n d other neoplasms (19).

T h e m o l e c u l a r structures

of v i n c a l e u k o b l a s t i n e a n d v i n -

cristine w e r e d e t e r m i n e d b y c h e m i c a l studies i n 1964 ( F i g u r e 4 ) a n d t h e c o m p l e t e stereochemistry

c i d a t e d b y x-ray c r y s t a l l o g r a p h i c analysis i n 1965 (21). blastine is o n e o f m o r e t h a n 5 0 a l k a l o i d s i s o l a t e d f r o m Vinca

Figure 4.

(20),

a n d absolute c o n f i g u r a t i o n w e r e e l u Vincaleukorosea.

Vincaleukoblastine

T h e r e v i e w o f t h e history of reserpine a n d v i n c a l e u k o b l a s t i n e reveals that e a c h a l k a l o i d w a s a m i n o r constituent of a c o m p l e x m i x t u r e a n d that its i s o l a t i o n f r o m t h e m i x t u r e w a s g u i d e d i n e a c h case b y assay f o r characteristic p h a r m a c o l o g i c a l properties.

It is l i k e l y that, h a d t h e i n v e s t i g a -


6

DRUG

tions of Rauwolfia

serpentina

a n d Vinca

DISCOVERY

rosea p r o c e e d e d a l o n g classical

p h y t o c h e m i c a l lines, w i t h o u t p h a r m a c o l o g i c a l g u i d a n c e , the

discovery

of reserpine a n d of v i n c a l e u k o b l a s t i n e w o u l d h a v e b e e n p o s t p o n e d b y m a n y years.

The Future: Vernolepin and Jatrophone T h e past a n d present states of a n y field are f a r s i m p l e r to c o m m e n t u p o n t h a n the f u t u r e . O n the other h a n d , the absence of clear-cut g u i d e lines p r o v i d e s the w r i t e r c o n s i d e r a b l e l a t i t u d e i n d i s c u s s i n g the f u t u r e . Downloaded by NEW YORK UNIV on May 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0108.ch001

B e l o w I o u t l i n e b r i e f l y some recent

findings

i n m y laboratory i n a

p r o g r a m d i r e c t e d at t u m o r i n h i b i t o r s of p l a n t o r i g i n . T h i s p r o g r a m , w h i c h has a l r e a d y l e d to the i s o l a t i o n of the a c t i v e p r i n c i p l e s of m o r e t h a n 80 t u m o r - i n h i b i t o r y extracts, has b e e n the subject of t w o recent r e v i e w s (22).

F o r this d i s c u s s i o n o f the f u t u r e of p l a n t - d e r i v e d d r u g s , the stories

of v e r n o l e p i n a n d jatrophone w i l l e x e m p l i f y one i m p o r t a n t a p p r o a c h . Powdered leaves A

(1.5

Kg)

ι Concentrated chloroform Β

extract

(87.0g) Partition

1

ι 10%

Aqueous

extract,

methanol

C (5l.0g) Silica

D

gel

Solvent:

Vernomenin

(6.5

g)

Mixture

(6.5

g)

Vernolepin

(5.5

g)

Figure 5.

Interfacial

(I0.6g)

Petroleum extract, Ε

ether (23.8 g)

chromatography

15%

Fractionation

1 solid

acetone

in

chloroform

of tumor-inhibitory

extract from Vernonia hymenolepis

I n o u r p r o g r a m , the f r a c t i o n a t i o n a n d i s o l a t i o n studies are g u i d e d at e v e r y stage b y b i o l o g i c a l assays. T h e systematic f r a c t i o n a t i o n has m a d e p o s s i b l e the i s o l a t i o n of i m p o r t a n t m i n o r constituents w h i c h w o u l d most p r o b a b l y h a v e b e e n m i s s e d i n the classical a p p r o a c h . D u r i n g the screen i n g p r o g r a m sponsored b y the C a n c e r C h e m o t h e r a p y N a t i o n a l Service C e n t e r , a n extract of Vernonia

hymenolepis,

A. rich, w a s f o u n d to s h o w

significant a n d r e p r o d u c i b l e c y t o t o x i c i t y against the K B tissue


culture

1.

Fiant

K U P C H A N

7

Sources

of h u m a n c a r c i n o m a o f the n a s o p h a r y n x .

F i g u r e 5 summarizes the frac

t i o n a t i o n p r o c e d u r e that l e d to t h e i s o l a t i o n o f t h e c y t o t o x i c p r i n c i p l e s , vernolepin, a n d vernomenin. A l t h o u g h the compounds were a n d i s o l a t e d solely o n t h e basis of in vitro

concentrated

cytotoxicity, vernolepin was

s u b s e q u e n t l y f o u n d to s h o w significant in vivo t u m o r i n h i b i t o r y a c t i v i t y against t h e W a l k e r 256 c a r c i n o s a r c o m a

i n t h e rat. V e r n o l e p i n a n d its

isomer, v e r n o m e n i n , w e r e i n t e r r e l a t e d b y c o n v e r s i o n to a c o m m o n m e t h a n o l a d d u c t . A c o m b i n a t i o n of d e g r a d a t i v e , spectral, a n d x-ray c r y s t a l l o graphic

studies

resulted

i n assignment

of t h e b i o g e n e t i c a l l y


e l e m a n o l i d e d i l a c t o n e structures s h o w n i n F i g u r e 6 (23,

Figure 6.

novel,

24).

Structures of vernolepin (upper left, R=H) and vernomenin right, R=H)

(upper

S e v e r a l recent observations h a v e f o c u s e d a t t e n t i o n o n t h e i m p o r t a n c e of t h e c o n j u g a t e d α - m e t h y l e n e lactone f u n c t i o n f o r t h e b i o l o g i c a l a c t i v i t y of v e r n o l e p i n a n d other sesquiterpene lactones.

F u r t h e r m o r e , the results

s u p p o r t the v i e w that t h e α - m e t h y l e n e lactones m a y exert t h e i r effects o n cells b y i n t e r a c t i n g w i t h s u l f h y d r y l enzymes that regulate c e l l u l a r g r o w t h . F o r instance, v e r n o l e p i n is a p o t e n t i n h i b i t o r of t h e extension g r o w t h of w h e a t c o l e o p t i l e sections (-25); this i n h i b i t o r y effect is b l o c k e d c o m p l e t e l y b y a d d i n g s u l f h y d r y l c o m p o u n d s s u c h as m e r c a p t o e t h a n o l t o t h e m e d i u m . S e c o n d , v e r n o l e p i n a n d other sesquiterpene lactones c a n i n h i b i t p h o s p h o fructokinase

b y reacting

with

t h e enzyme's

sulfhydryl

groups

(26).

T h i r d , as s h o w n i n F i g u r e 7, the c y t o t o x i c i t y of v e r n o l e p i n d e r i v a t i v e s appears to b e r e l a t e d d i r e c t l y to t h e presence of free c o n j u g a t e d α - m e t h ylene

lactone

functions.

Thus,

selective

r e d u c t i o n of t h e e t h y l i d e n e


8

DRUG

0

0'

0'

ο


ED

DIHYDROVERNOLEPIN

TETRAHYDROVERNOLEPIN

2.0/

2.0 /

5 0

ο

ο

VERNOLEPIN

DISCOVERY

19.0/

Ο'

Ο

Ο

Ο

3

ACIDIC METHANOLYSIS

HEXAHYDROVERNOLEPIN >

OCH

PRODUCT

100/

26/

Figure 7.

Cytotoxicity

of vernolepin

derivatives

d o u b l e b o n d does n o t a p p e a r to affect the c y t o t o x i c i t y . H o w e v e r , m o d i fication

of the a - m e t h y l e n e - y - l a c t o n e ( b y trans-esterification to t h e m e t h

anol adduct or b y hydrogénation) cytotoxicity.

results i n a 1 0 - f o l d d i m i n u t i o n i n

M o d i f i c a t i o n of b o t h α - m e t h y l e n e lactone

systems, as i n

h e x a h y d r o v e r n o l e p i n , leads to a d e r i v a t i v e w h i c h is essentially i n a c t i v e . [ T h e synthesis of d i h y d r o v e r n o l e p i n exemplifies a n e w b l o c k i n g sequence f o r the p r o t e c t i o n of the h i g h l y r e a c t i v e c o n j u g a t e d α - m e t h y l e n e g r o u p s of lactones ( F i g u r e 8 ). V e r n o l e p i n w a s treated w i t h excess n - p r o p y l t h i o l at p H 9.2 to g i v e a b i s t h i o l a d d u c t . H y d r o g é n a t i o n o f the b i s t h i o l a d d u c t ( w i t h one m o l e e q u i v a l e n t of h y d r o g e n ) , f o l l o w e d b y m e t h y l i o d i d e m e t h y l a t i o n a n d s o d i u m b i c a r b o n a t e - c a t a l y z e d e l i m i n a t i o n , gave d i h y d r o vernolepin

(-27).]

R e c e n t l y w e s t u d i e d the reactions

of several c o n -

j u g a t e d α - m e t h y l e n e lactones w i t h m o d e l b i o l o g i c a l n u c l e o p h i l e s , s u c h as cysteine, l y s i n e , a n d g u a n i n e (28).

T h i o l s s u c h as cysteine w e r e the most

r e a c t i v e , a n d the rate of r e a c t i o n w a s of the same o r d e r as that of cysteine w i t h iodoacetate, a c o m m o n l y u s e d s u l f h y d r y l reagent

(Figure 9).

The

b i s c y s t e i n e a d d u c t s , i n a c c o r d w i t h expectations, w e r e essentially i n a c t i v e . E x t r a c t s of Jatropha

gossypiifolia

L . a n d r e l a t e d species h a v e b e e n

u s e d f o r m a n y years i n C o s t a R i c a to treat cancerous g r o w t h s . A n alco h o l i c extract of the roots of Jatropha

gossypiifolia

( s u p p l i e d b y J . A . Saenz

R e n a u l d of the U n i v e r s i t y of C o s t a R i c a ) w a s f o u n d b y C C N S C to s h o w i n h i b i t o r y a c t i v i t y against f o u r s t a n d a r d a n i m a l t u m o r systems ( s a r c o m a 180, L e w i s l u n g c a r c i n o m a , a n d l y m p h o c y t i c l e u k e m i a P-388 i n the m o u s e , a n d the W a l k e r 256 i n t r a m u s c u l a r c a r c i n o s a r c o m a i n t h e r a t ) a n d in


vitro

1.

κυρ C H A N

Fhnt

9

Sources

against cells d e r i v e d f r o m h u m a n c a r c i n o m a of t h e n a s o p h a r y n x ( K B ) . F i g u r e 10 s u m m a r i z e s t h e f r a c t i o n a t i o n p r o c e d u r e that l e d to t h e isola t i o n of the c y t o t o x i c p r i n c i p l e , jatrophone. of f r a c t i o n a t i o n

g u i d e d b y assay against

A f t e r i s o l a t i o n o n the basis K B cell culture,

jatrophone


s h o w e d r e p r o d u c i b l e i n h i b i t o r y a c t i v i t y against the P-388 l y m p h o c y t i c

Dihydrovernolepin

1^

Figure 8.

NH RSH=

/

Dihydrovernolepin

3

CH-CH -SH

C0

Figure 9.

ά

2

2

Reaction of vernolepin with ^cysteine at 25°C, pH 7.4. reaction rate: k = 12,000 liters/mole/min. 2


Initial

10

DRUG

Concentrated a l c o h o l i c A

DISCOVERY

extract

(740g) Trituration

Benzene Β

solubles

Benzene

(165g)

C

insolubles

(570g)

Trituration

Hexane s o l u b l e s

Hexane i n s o l u b l e s


D (93g)

Ε (70g)

Chromatography

(Silica gel)

Chroma t o g r a p h y F (48g)

+

Jatrophone

(Alumina)

Figure 10.

Fractionation

G

of tumor-inhibitory piifolia L .

(l.4g)

extract from Jatropha gossy

l e u k e m i a as w e l l . T h e n o v e l m a c r o c y c l i c d i t e r p e n o i d structure s h o w n i n F i g u r e 11 w a s assigned o n t h e basis of s p e c t r a l studies of j a t r o p h o n e a n d several d e r i v a t i v e s , as w e l l as x-ray c r y s t a l l o g r a p h i c analysis of jatrophone d i h y d r o b r o m i d e (29).

H y d r o b r o m i n a t i o n of jatrophone i n g l a c i a l acetic

a c i d gives t h e u n i q u e d i h y d r o b r o m i d e a d d u c t ; s t i r r i n g a c h l o r o f o r m solu t i o n of t h e d i h y d r o b r o m i d e w i t h a suspension of n e u t r a l a l u m i n a r e g e n erates jatrophone.

T h e r e a d y f o r m a t i o n of t h e d i h y d r o b r o m i d e a d d u c t

is e n v i s i o n e d as a result of t w o n o v e l t r a n s a n n u l a r conjugate

addition

reactions, a n d t h e s t e r e o c h e m i c a l r e p r e s e n t a t i o n of these conjugate a d d i tions is s h o w n i n F i g u r e 12. T h i o l s attack jatrophone w i t h great ease, a n d studies of the i n t e r a c t i o n o f s u l f h y d r y l enzymes w i t h j a t r o p h o n e are c u r r e n t l y u n d e r w a y . T h e s e a n d other experiments are d e s i g n e d to e v a l -

o JATROPHONE Figure 11.

Antileukemic

JATROPHONE

DIHYDROBROMIDE

principle of Jatropha gossypiifolia


1.

KUPCHAN

11

Ρ font Sources

uate w h e t h e r j a t r o p h o n e a n d other p l a n t - d e r i v e d t u m o r i n h i b i t o r s m a y act b y selective a l k y l a t i o n of s u l f h y d r y l e n z y m e s that regulate

cellular

growth. T h i s d i s c u s s i o n of v e r n o l e p i n a n d jatrophone illustrates o u r a p p r o a c h to the i s o l a t i o n f r o m plants of n e w , n o v e l , a n d b i o l o g i c a l l y active n a t u r a l p r o d u c t s . B o t h examples i n v o l v e d b i o l o g i c a l assays for g r o w t h - i n h i b i t o r y a c t i v i t y , b u t a n y other satisfactory b i o l o g i c a l assay c o u l d b e u s e d i n a search for other types of c o m p o u n d s . T o the investigator w h o w i l l u n d e r


take s u c h a systematic a p p r o a c h to b i o l o g i c a l l y active n a t u r a l p r o d u c t s ,

Figure 12.

Transannular conjugate additions of Η Br

the p l a n t k i n g d o m represents a v i r t u a l l y u n t a p p e d resource.

O u r botanist

colleagues estimate that a p p r o x i m a t e l y 500,000 species of plants a n d that p e r h a p s 1 0 %

occur,

h a v e b e e n i n v e s t i g a t e d p h y t o c h e m i c a l l y . O f the

s m a l l m i n o r i t y w h i c h h a v e r e c e i v e d c h e m i c a l attention, o n l y a t i n y p r o p o r t i o n h a v e ever b e e n a t t a c k e d w i t h a systematic a p p r o a c h i n v o l v i n g a n y t y p e of b i o l o g i c a l assay.

D i f f e r e n t bioassays w i l l p r o v i d e " h a n d l e s "

for i s o l a t i n g n e w c o m p o u n d s f r o m those f e w plants w h i c h h a v e a l r e a d y b e e n e x a m i n e d w i t h the g u i d a n c e of one assay system.

Indeed, w e have

a l r e a d y w i t n e s s e d the effectiveness of this a p p r o a c h i n the p l a n t t u m o r inhibitor program.

Periodic reexamination

of p l a n t recollections

n e w screening systems continues to y i e l d n e w actives.

with

A s one looks to

the f u t u r e , p l a n t sources m a y p r o v e to be i n e x h a u s t i b l e since p e r i o d i c r e e x a m i n a t i o n of extracts of the same p l a n t w i l l be d e s i r a b l e as n e w a n d sensitive bioassay p r o c e d u r e s for different types of a c t i v i t y are d i s c o v e r e d .


12

DRUG

DISCOVERY

O n e i m p o r t a n t q u e s t i o n r e m a i n s : w h e r e w i l l the n e w leads from?

come

So m a n y of the o l d e r p l a n t - d e r i v e d m e d i c i n a l s h a v e s p r u n g f r o m

f o l k remedies that m a n y readers assume that o n l y plants r e p o r t e d to be therapeutically useful should be examined for pharmacological proper ties.

Selected i n d i v i d u a l f o l k remedies w h o s e r e p o r t e d p h a r m a c o l o g i c a l

p r o p e r t i e s are d e t e c t a b l e i n objective assays w i l l c o n t i n u e to p r o v i d e some leads.

H o w e v e r , logistic considerations w i l l r e q u i r e that the m a j o r i t y of

f u t u r e leads i n this area w i l l emerge f r o m large scale r a n d o m screening of p l a n t extracts.

It is significant that of the first 40,000 c r u d e extracts

p r e p a r e d f r o m plants c o l l e c t e d b y the C C N S C r a n d o m l y f r o m a r o u n d Downloaded by NEW YORK UNIV on May 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0108.ch001

the w o r l d a p p r o x i m a t e l y 3 % s h o w e d r e p r o d u c i b l e a c t i v i t y i n one or a n other of the t u m o r systems u s e d ( 3 0 ) .

T h e d e m o n s t r a t e d effectiveness of

r a n d o m screening of p l a n t extracts i n u n c o v e r i n g significant leads

for

systematic i s o l a t i o n of g r o w t h - i n h i b i t o r y c o m p o u n d s supports confidence i n this a p p r o a c h to n e w c o m p o u n d s w i t h other d e s i r e d p h a r m a c o l o g i c a l properties. O u r s m a l l i n c u r s i o n i n t o the search for p l a n t - d e r i v e d t u m o r i n h i b i t o r s d u r i n g the past d e c a d e has y i e l d e d a f a s c i n a t i n g a r r a y of n o v e l b i o l o g i c a l l y active n a t u r a l p r o d u c t s .

T h e plant k i n g d o m w i l l continue

to

y i e l d n o v e l d r u g s to those w h o w i l l use b i o l o g i c a l assay as a " d i v i n i n g r o d " i n their h i g h l y significant a n d c h a l l e n g i n g explorations.

Literature Cited (1) Gulland, J. M., Robinson, R., Mem. Proc. Manchester Lit. Phil. Soc. (1925) 69, 79. (2) Gates, M., Tschudi, G., J. Am. Chem. Soc. (1952) 74, 1109; (1956) 78, 1380. (3) Elad, D., Ginsburg, D., J. Chem. Soc. (1954) 3052. (4) Turner, R. B., Woodward, R. B., The Alkaloids (1953) 3, 1. (5) Woodward, R. B., von E. Doering, W., J. Am. Chem. Soc. (1944) 66, 849; (1945) 67, 860. (6) Russell, P. B., in "Medicinal Chemistry," A. Burger, Ed., p. 821, 2nd ed., Interscience, New York, 1960. (7) Siddiqui, S., Siddiqui, R. H., J. Indian Chem. Soc. (1931) 8, 667; (1932) 9, 539; (1935) 12, 37. (8) Woodson, R. E., Jr., Youngken, H. W., Schlittler, E., Schneider, J. Α., "Rauwolfia," Little, Brown, & Co., Boston, 1957. (9) Chopra, R. N., Chakravarti, M., Indian J. M. Res. (1941) 29, 763. (10) Chopra, R. N., Gupta, J. C., Bose, B. C., Chopra, I., Indian J. M. Res. (1943) 31, 71. (11) Vakil, R. J., British Heart J. (1949) 11, 350. (12) Mueller, J. M., Schlittler, E., Bein, H. J., Experientia (1952) 8, 338. (13) Dorfman, L. A. et al., Helv. Chim. Acta (1954) 37, 59. (14) Woodward, R. B., Bader, F. E., Bickel, H., Frey, A. J., Kierstad, R. W., J. Am. Chem. Soc. (1956) 78, 2023, 2657. (15) Woodward, R. B., Bader, F. E., Bickel, H., Frey, A. J., Kierstad, R. W., Tetrahedron (1958) 2, 1.



1.

κυρ

CHAN

Ρ font Sources

13

(16) Noble, R. L., Beer, C. T., Cutts, J. H., Biochem. Pharmacol. (1958) 1, 347. (17) Johnson, I. S., Wright, H. F., Svoboda, G. H., J. Lab. Clin. Med. (1959) 54, 830. (18) Svoboda, G. H., Johnson, I. S., Gorman, M., Neuss, N., J. Pharm. Sci. (1962) 51, 707. (19) National Advisory Cancer Council Report, "Progress Against Cancer, 1969," U. S. Department of Health, Education, and Welfare, Washing ton, D. C. (20) Neuss, N., Gorman, M., Hargrove, W., Cone, Ν. J., Biemann, Κ., Buchi, G., Manning, R. Ε., J. Am. Chem. Soc. (1964) 86, 1440. (21) Moncrief, J. W., Lipscomb, W. N., J. Am. Chem. Soc. (1965) 87, 4963. (22) Kupchan, S. M., Trans. Ν.Y. Acad. Sci. (1970) 32, 85; Pure Appl. Chem. (1970) 21, 277. (23) Kupchan, S. M., Hemingway, R. J., Werner, D., Karim, Α., J. Org. Chem. (1969) 34, 3903. (24) Kupchan, S. M., Hemingway, R. J., Werner, D., Karim, Α., McPhail, A. T., Sim, G. Α., J. Am. Chem. Soc. (1968) 90, 3596. (25) Sequeira, L., Hemingway, R. J., Kupchan, S. M., Science (1968) 161, 789. (26) Hanson, R. L., Lardy, Η. Α., Kupchan, S. M., Science (1970) 168, 378. (27) Kupchan, S. M., Giacobbe, T. J., Krull, I. S., Tetrahedron Letters (1970) 2859. (28) Kupchan, S. M., Fessler, D. C., Eakin, Μ. Α., Giacobbe, T. J., Science (1970) 168, 376. (29) Kupchan, S. M., Sigel, C. W., Matz, M. J., Saenz Renauld, J. Α., Haltiwanger, R. C., Bryan, R. F., J. Am. Chem. Soc. (1970) 92, 4476. (30) Hartwell, J. L., Abbott, B. J., Advan. Pharmacol. Chemother. (1969) 7, 117. RECEIVED November 5, 1970.


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