Glucosinolates and Other Naturally Occurring - American Chemical

2 Glucosinolates and Other Naturally Occurring O-Sulfates ANDERS KJAER

Downloaded by NORTH CAROLINA STATE UNIV on November 8, 2013 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0077.ch002

Department of Organic Chemistry, The Technical University of Denmark, 2800 Lyngby, Denmark

The following discussion will be restricted to sulphates of natural provenance. Carbohydrate sulphates, the legitimate topic of this symposium, quantitatively dominate the class of naturally occurring, organic sulphates but by no means represent it fully. To be sure, the typical C - O - S ester linkage is also encountered in a vast and rapidly increasing number of other known sulphates of animal and plant origin. Moreover, chemical entities exhibiting other structural features, such as P - O - S , N - O - S , and N - S - l i n k a ges, are also known as natural products. The ensuing discussion w i l l c e n t r e on the g l u c o s i n o l a t e s 1, a u n i q u e l y c o n s t i t u t e d and

well-defined class of anions occurring as plant products that are, at the same time, organic sulphates and glucose derivatives, yet assembled in a fashion so unorthodox that the raison d ' ê t r e for their presentation at this symposium may appear tenuous. The chemical character and biological degradation of glucosinolates, however, exhibit features of potential interest to carbohydrate sulphate chemistry; these aspects will be emphasized. The discussion will also include a brief, up-to-date survey of some other organic sulphates, selected to indicate the scope of structural variation encountered within the living world. Glucosinolates The collection of glucosinolates, thus far comprising about seventy-five individual anions, exclusively encountered in higher 0-8412-0426-8/78/47-077-019$05.00/0 © 1978 American Chemical Society

In Carbohydrate Sulfates; Schweiger, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20

CARBOHYDRATE SULFATES

plants, p o s s e s s e s a r e m a r k a b l e s t r u c t u r a l u n i f o r m i t y . T h u s , the β -D-thioglucopyranosidic

l i n k a g e , the h y d r o x y l a m i n e - O - s u l p h a t e

m o i e t y , and the ( Z ) - t h i o h y d r o x i m a t e a r r a n g e m e n t p r e s e n t i n 1 a r e c h e m i c a l f e a t u r e s to w h i c h no known e x c e p t i o n

e x i s t s . Hence, the

s i d e - c h a i n R of 1 c o n s t i t u t e s the s o l e s t r u c t u r a l p a r a m e t e r . T h i s


r e m a r k a b l e c h e m i c a l u n i f o r m i t y r e f l e c t s , a l m o s t by n e c e s s i t y , a corresponding s i m i l a r i t y in biosynthetic derivation. Few p a t h w a y s i n h i g h e r p l a n t s have b e e n c l a r i f i e d i n g r e a t e r

anabolic detail

+

than those l e a d i n g f r o m α - a m i n o a c i d s , R* C H ( N H g ) C 0 " ~ , to g l u 2

c o s i n o l a t e s 1, t h r o u g h a s e q u e n c e of steps o u t l i n e d i n S c h e m e 1.

R 1 Scheme 1 Ox

R C H - (NH ) -C0 3

+

2

> R-CH-(NHOH) -C0 H

Ox

-C02 [R-CH-(NO)-C0 H]

2

R-CH(S-Glu):NOH
—H 0 2

10,

R =

CH =CH

II

R =

C H

2

6

5

I n t r i g u i n g l y , the a m i n o a c i d s p r o d u c e d c o n t a i n e x c e s s of the L-isomers,

r e f l e c t i n g s o m e s t e r i c c o n t r o l f r o m the g l u c o s e

ring,

the o n l y c h i r a l m o i e t y i n v o l v e d i n the r e a c t i o n . S e v e r a l g l u c o s i n o l a t e s have b e e n s y n t h e s i z e d . A c h a r a c t e r i s t i c f e a t u r e of a l l the a p p r o a c h e s i s the i n t r o d u c t i o n of the s u l p h a t e - g r o u p i n g at the f i n a l stage of the s y n t h e t i c sequence, n o r m a l l y with the S O g - p y r i d i n e c o m p l e x a s a r e a g e n t . In t h i s r e s p e c t the a p p r o a c h s i m u l a t e s the b i o s y n t h e t i c a s s e m b l a g e ; h e r e , i n the v e r y l a s t step ( S c h e m e l ) , t h e sulphate r e s i d u e i s t r a n s f e r r e d f r o m 3'-phosphoadenosine 5'-phosphosulphate to the o x y g e n a t o m of the h y d r o x y l a m i n e g r o u p i n g i n a r e a c t i o n p r o b a b l y

catalyzed

by the s a m e e n z y m e f o r the whole r a n g e of g l u c o s i n o l a t e s (5a). P u r e glucosinolate salts are non-volatile, high-melting

com

pounds, r e a d i l y s o l u b l e i n w a t e r b y v i r t u e of t h e i r c o m b i n e d g l u c o s i d e a n d salt c h a r a c t e r ; t h e i r r e a d i n e s s to c r y s t a l l i z e i s c a p r i c i o u s and not a l w a y s v e r y p r o n o u n c e d . In no c a s e have

s u g a r s o-

t h e r than g l u c o s e b e e n o b s e r v e d i n the t h i o g l y c o s i d i c l i n k a g e of


CARBOHYDRATE

24

SULFATES

n a t u r a l l y o c c u r r i n g g l u c o s i n o l a t e s . E q u a l l y constant i s the s u l phate r e s i d u e ; the a n a l o g o u s phosphate e s t e r s , a p r i o r i not unr e a s o n a b l e a l t e r n a t i v e s , have n e v e r been e n c o u n t e r e d . l t

i s temp-

t i n g to a s s u m e that the r a i s o n d'être f o r the sulphate g r o u p i n g i n the g l u c o s i n o l a t e i s i t s c h a r a c t e r

of an e x c e l l e n t l e a v i n g group.


P u r s u i n g t h i s l i n e of s p e c u l a t i o n , the t r u e b i o l o g i c a l f u n c t i o n of the g l u c o s i n o l a t e s m a y h e n c e be that of s e r v i n g as d e p o s i t o r i e s of v o l a t i l e r e a c t i o n p r o d u c t s , p o s s e s s i n g

specific biological pro-

p e r t i e s and a r i s i n g f r o m the e n z y m i c a l l y

initiated degration r e -

a c t i o n s d i s c u s s e d above. In fact, m u c h knowledge h a s a c c u m u l a t e d o v e r the y e a r s to i n d i c a t e that i s o t h i o c y a n a t e s , and p e r h a p s other d e g r a d a t i o n

products as well, play a d e c i s i v e r o l e i n seve-

r a l w e l l - e s t a b l i s h e d and s p e c i f i c p a r a s i t e - h o s t r e l a t i o n s w i t h i n i m p o r t a n t p l a n t s of the c r u c i f e r f a m i l y . O b v i o u s l y , s u c h f u n c t i o n s w i l l p e r se a t t r i b u t e to the g l u c o s i n o l a t e s a p h y l o g e n e t i c

signifi-

c a n c e that w o u l d m a k e t h e i r d i s c o n t i n u o u s n a t u r a l d i s t r i b u t i o n w i t h i n the plant k i n g d o m l e s s s u r p r i s i n g . O t h e r O r g a n i c Sulphates of P l a n t O r i g i n A few r e p r e s e n t a t i v e s of other g r o u p s of o r g a n i c

sulphates,

o c c u r r i n g i n h i g h e r p l a n t s s e l e c t e d r a t h e r a r b i t r a r i l y by an o r ganic c h e m i s t p r i m a r i l y c o n c e r n e d with s t r u c t u r a l a s p e c t s , m a y s e r v e as an i l l u s t r a t i o n of the v e r s a t i l i t y and s c o p e of o r g a n i c s u l p h a t e s e n c o u n t e r e d e v e n w i t h i n the l i m i t e d g r o u p of l i v i n g spec i e s m a d e up by h i g h e r p l a n t s . C h o l i n e sulphate ,12 a c c u m u l a t e s , to the extent of m o r e than o n e - t h i r d of the t o t a l amount of sulphate fed, i n the r o o t s of s u l p h u r - d e f i c i e n t p l a n t s of c o r n , b a r l e y , and s u n f l o w e r , e v e n u n d e r s t e r i l e c o n d i t i o n s . In n o n - d e f i c i e n t r o o t s , and i n a l l l e a v e s , it a c counts f o r 5-15 % of the t o t a l , s o l u b l e s u l p h u r compounds. A n i m p o r t a n t r o l e of 1.2 a s an e f f e c t i v e t r a n s p o r t agent f o r p a s s a g e t h r o u g h the c e l l m e m b r a n e h a s b e e n s u g g e s t e d (11). A d r a m a t i c d e v e l o p m e n t i n o u r knowledge of f l a v o n o i d s u l phates i n h i g h e r plants s h o u l d not p a s s u n n o t i c e d h e r e . M o r e than


2.

KJAER

Glucosinolates and

25

Other O-Sulfates

40 y e a r s ago, p e r s i c a r i n ( i s o r h a m n e t i n

3-sulphate) 13 was

repor-

t e d as a constituent of w a t e r - p e p p e r ( P o l y g o n u m h y d r o p i p e r ) (12); the i s o l a t i o n of only few

a d d i t i o n a l and

scattered flavonoid

sulpha-

t e s m a d e t h e s e s t r u c t u r e s i n t r i g u i n g enough to p r o m p t the s t a t e ment, i n 1971, that 'flavonoid b i s u l p h a t e s a r e a m o n g s t the r a r e s t


of n a t u r a l l y o c c u r r i n g f l a v o n o i d s ' (_13). In the s a m e y e a r , h o w e v e r , a v e r i t a b l e l a n d s l i d e of d i s c o v e r y

set in, t r i g g e r e d by D r . J . B.

H a r b o r n e and h i s a s s o c i a t e s and r e s u l t i n g i n a p r o f o u n d r e v i s i o n of our v i e w of these c o m p o u n d s . F l a v o n o i d

s u l p h a t e s now

r e g a r d e d , not as p h y t o c h e m i c a l o d d i t i e s , but r a t h e r as an

must

be

impor-

tant c l a s s of n a t u r a l c o m p o u n d s . T h u s , i n a r e c e n t r e v i e w (14) i n dividual flavonoid sulphates

'detected v a r i o u s l y i n o v e r 200

spe-

c i e s f r o m 20 plant f a m i l i e s ' a r e l i s t e d , and undoubtedly m a n y r e a r e l i k e l y to a p p e a r . T h i s e x a m p l e i l l u s t r a t e s how l a r g e g r o u p of n a t u r a l p r o d u c t s m a y

mo-

readily a

be o v e r l o o k e d b e c a u s e of

n e g l e c t on the p a r t of the c h e m i s t , i n the p r e s e n t c a s e undoubtedl y c a u s e d by the s a l t c h a r a c t e r

and o v e r - a l l i n c o n s p i c u o u s n e s s

of the compounds. F l a v o n o l s and f l a v o n e s , as s u c h o r i n g l y c o s i d i c f o r m , with one the 3-OH

and 7-OH,

o r m o r e sulphate

r e s i d u e s attached, m o s t l y at

but o c c a s i o n a l l y a l s o l i n k e d to the

sugar

m o i e t y , a r e p r e v a l e n t a m o n g the f l a v o n o i d s u l p h a t e s known thus far. The

p o s s i b i l i t y of f l a v o n o i d s u l p h a t e s h a v i n g an i m p o r t a n t

f u n c t i o n i n salt uptake and m e t a b o l i s m , i n a d d i t i o n to that of c o n f e r r i n g w a t e r s o l u b i l i t y to o t h e r w i s e i n s o l u b l e f l a v o n o i d s , h a s b e e n s u g g e s t e d i n v i e w of t h e i r p r e f e r r e d o c c u r r e n c e w i t h i n p l a n t s with aquatic, often s a l i n e h a b i t a t s .

•

OMe


26


O t h e r p l a n t s p h e n o l i c s , r e c o g n i z e d as sulphate

conjugates,

i n c l u d e the i s o m e r i c c h l o r o g e n i c a c i d O - s u l p h a t e s 14 (14); O - s u l p h a t e s d e r i v i n g f r o m 1 - c a f f e y l g l u c o s e ,15 and p - c o u m a r y l glucose

16 (14), as w e l l a s the 3/-Q,?) (.15) and 6'-Ο-sulphate 18

(16) of betanin, a p i g m e n t c h a r a c t e r i s t i c of m e m b e r s of the taxo-


nomically restricted order

Centrospermae.

1~L R = OH 16

R =Η

A p p l i c a t i o n of p a p e r e l e c t r o p h o r e s i s technique

to e x t r a c t s of

s e v e r a l s p e c i e s of the f a m i l y P o l y g o n a c e a e r e c e n t l y l e d to the r e c o g n i t i o n of c o v a l e n t l y bound sulphate i n h a l f of 27 s p e c i e s stu died, b e l o n g i n g to the genus R u m e x . F r o m one of these a n O - s u l phate of e m o d i n 1 (or 8 ) - g l u c o s i d e ,19 and a d i g l u c o s i d e s u l p h a t e of the c o r r e s p o n d i n g

e m o d i n dianthrone

w e r e c h a r a c t e r i z e d , both

c o n t a i n i n g the sulphate r e s i d u e i n the g l u c o s e m o i e t i e s

(17).

Η

V7_ R = S 0 " j R = Η 1

3

Jj^

R = H , R

1

= SO3"


2.

KJAER

Glucosinolates and

27

Other O-Sulfates

Conclusion Our

knowledge about c o v a l e n t l y bound s u l p h a t e s i s o b v i o u s -

l y i n i t s i n f a n c y . We

know that s u l f o h y d r o l a s e s , e n z y m e s c a t a l y -

z i n g the h y d r o l y s i s of o r g a n i c sulphates, a r e w i d e - s p r e a d throughout the w o r l d s of m i c r o o r g a n i s m s , p l a n t s and a n i m a l s .


our u n d e r s t a n d i n g of these and r e l a t e d e n z y m e s h a s r e m a r k a b l y r e c e n t l y we

Although

increased

a r e s t i l l left with the r a t h e r p a r a d o x i c a l

situation: many e n z y m e s lack w e l l - r e c o g n i z e d n a t u r a l substrates and, at the s a m e t i m e , n a t u r a l s o u r c e s p r o v i d e o r g a n i c

sulphates

f o r w h i c h no e n z y m i c a p p a r a t u s s e e m s to e x i s t . O b v i o u s l y , c o n t i n u e d e f f o r t s to c l a r i f y the d i s t r i b u t i o n , c h e m i s t r y

and

enzymic

t r a n s f o r m a t i o n of n a t u r a l l y o c c u r r i n g s u l p h a t e s cannot f a i l to be r e w a r d i n g to those p o s s e s s i n g the i m a g i n a t i o n , s k i l l and

perseve-

r a n c e n e e d e d to h e l p us u n d e r s t a n d the i m p o r t a n c e and

biological

f u n c t i o n of these

compounds.

Abstract The

chemistry

of the g l u c o s i n o l a t e s , a c l a s s of n a t u r a l l y oc-

c u r r i n g t h i o g l u c o s i d es c o n t a i n i n g an

O - s u l p h a t e grouping, i s

b r i e f l y d i s c u s s e d . T h e i r e n z y m i c d e g r a d a t i o n to i s o t h i o c y a n a t e s , and n i t r i l e s ,

as w e l l as other r e a c t i o n s i n w h i c h the

sulphate

g r o u p i n g p a r t i c i p a t e s , a r e r e v i e w e d . O t h e r c l a s s e s of O - s u l p h a tes, o c c u r r i n g i n h i g h e r p l a n t s , a r e l i s t e d , i n c l u d i n g f l a v o n o i d sulphates. cussed

The

p o s s i b l e r ô l e of o r g a n i c s u l p h a t e s i s b r i e f l y

and future r e s e a r c h a s p e c t s

dis-

adumbrated.

Literature Cited 1. 2.

Kjær, A., Fortschr. Chem. Org. Naturst., (1960) 18, 122. Ettlinger, M. G. and Kjær, A. in "Recent Advances in Phytochemistry", Vol. I, p. 89, Mabry, T. J., Alston, R. E. and Runeckles, V. C., Ed., Appleton-Century-Crofts, New York, Ν. Y. (1968).


28

3.


4.

5.

6. 7. 8. 9.

10. 11. 12. 13. 14.

15. 16. 17.


Kjær, A. in "Chemistry in Botanical Classification", Nobel Symposium 25, p. 229, Bendz, G. and Santesson, J., Ed., Academic Press, New York and London (1974). Kjær, A. in "The Biology and Chemistry of the Cruciferae", p. 207, Vaughan, J. G., MacLeod, A. J. and Jones, B. M. G., Ed., Academic Press, London, New York, San Francisco (1976). Kjær, A. and Olesen Larsen, P. in "Biosynthesis", Specialist Periodical Report, The Chemical Society, London, (a) (1973) 2, 95; (b) (1976) 4, 200 (c) (1977) 5, in press. Daniher, F. A. J. Org. Chem., (1969) 34, 2908. Maeda, Y. personal communication. Schneider, W. and Wrede, F. Ber. Deut. Chem. Ges., (1914) 47, 2225. Lundeen, A. J. "The Structure of the Mustard Oil Glucosides and Synthesis of the Glucotropaeolate Ion" Ph. D. Thesis, The Rice Institute, Houston, Texas (1957). Friis, P., Olesen Larsen, P. and Olsen, C. E. J. Chem. Soc., Perk. I, (1977) 661. Nissen, P. and Benson, A. A. Science, (1961) 1759. Kawaguchi, R. and Kim, K. W. J. Pharm. Soc. Japan, (1937) 57, 108. Saleh, N. A. M . , Bohm, B. A. and Ornduff, R. Phytochemistry (1971) 10, 611. Harborne, J. B. in "Progress in Phytochemistry", Vol. IV, p. 189, Reinhold, L., Harborne, J. B. and Swain, T., Ed., Pergamon Press, Oxford, New York, Toronto, Sydney, Paris and Frankfurt (1977). Imperato, F. Phytochemistry, (1975) 14, 2526. Wyler, Η., Rosler, H . , Mercier, M. and Dreiding, A. S. Helv. Chim. Acta (1967) 50, 545. Harborne, J. B. and Mokhtari, N. Phytochemistry (1977) 16, 1314.

RECEIVED February 6, 1978.


Glucosinolates and Other Naturally Occurring - American Chemical

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