mass spectroscopy of natural products. vi—localization of functional groups in the hopane skeleton

Mass Spectroscopy of Natural Products VI-Localization of Functional Groups in the Hopane Skeleton?

J. Schmidt and S. Huneck Research Centre for Molecular Biology and Medicine of the Academy of Sciences of the GDR, Institute of Plant Biochemistry, 402 Halle/S., Weinberg 3, GDR

The mass spectral fragmentation of hopane derivatives with oxygenated substituents at C-3, C-6, C-7, C-15, C-16 and C-22 is discussed. It is shown, that the positions of functional groups in rings A and B or D and E respectively can be distinguished using several derivatives and deuterated analogues.

INTRODUCTION

Mass spectrometry represents an unique tool both for skeletal assignments and for recognition and location of functional groups in pentacyclic triterpenes. 1-3 The principal fragmentation of hopanes was used by Cor- bett et aLk6 and Yosioka et aL7 in structural investiga- tions of such compounds.

This paper deals with the fragmentation behaviour of hopanes with substituents (hydroxy, 0x0 function) at C-3, C-6, C-7, C-15, C-16 and C-22. The possibil- ity of localization of a functional group is discussed with particular reference to distinguishing substituents at positions 3, 6 , 7 (rings A, B) and 15,16 (ring D), respectively. In addition, a comparison of positive and negative ion mass spectra is given.

19 20

Hopane

Position of functional groups Compound -OH =O C=C D

1 2 3 3b 4 4a 5 6 7 8 9a 10 lob 11 lla

22

22 22 3P 3P

3622

6a.22 6822

22 22

7822 7822

3 3 2 d P

17,21 17,21 3 a

3 11,21 3 21.22 3 22

6 a 6 6 501; lci,lP

Iff

t For Part V see: J. Schmidt and S. Huneck, Org. Mass Spectrom. 14,6415 (1 979).

Compound -OH

12 22 12b 22 13 15a,22 14s 15 P,22 15 22 15b 22 16 6cr,16P,22 17a 6p716p,22 18 16&22

Position of functional groups =O G=C D

7 7 6a.66

1501 15 15 16a,16@

6a 6

~

RESULTS AND DISCUSSION

In addition to substituent elimination hopane derivatives show favoured cleavages across ring C leading to fragment ions of type a and b (Scheme 1). These ions are of even mass in the dihydroxy compounds 2, 8, 11 and reveal the corresponding shifts in the derivatives investigated. Ion b suffers further decomposition to ( b - H,O) and ( b - C3H,0), representing the base peak in many cases (Table 1). An ion of type c which may be explained by the scission of three bonds in conjunction with a double hydrogen transfer from the charged species, was also observed in the mass spectra of taraxastanes8 Ion c appearing very abundantly in the derivatives with a double bond between C-17 and C-21 (4, 4a, 5) is probably originated via an allylic cleavage (Scheme 2). Further significant ions in 4 and 5 comprising ring E are d and e. The formation of an intense [M-C3H7]+ ion as indicated in compounds 4-7 was discussed previously by Galbraith et aL9 in moretane derivatives. ([M - H,O]”ions are due partly to thermal decomposition.)

A specific ion formed by scission across ring B (a-cleavage at C-6) appears in zeorin (8):

m/z 153 (28%) (8) (9a, 17a)

+OH

m/z 153 (28%) (8) (9a, 17a)

+OH

Although in leucotylin (16) the ion at m/z 151 represents the base peak (see below), the ion at m/z 153 is significant as indicated by the mass spectrum of the deuterated epimer 17a (see also Fig. 5) . In contrast to

CCC-0030-493X/19/0014-656$03.50

656 ORGANIC MASS SPECTROMETRY, VOL. 14, NO. 12, 1979 @ Heyden & Son Ltd, 1979

v)

3 5 v) v) v)

V

rn

Tab

le 1

. Typ

ical

frag

men

t ion

s of

the

hopa

nes i

nves

tigat

ed [m

/z ("

/")I

1

2 3

4=

5b

6"

76

8 10

11

12

13

15

1 6e

18"

3

[M -

CH

J '

413(

10)

429(

16)

427(

18)

41 l(

43

) 40

9(22

) 40

9(20

) 40

9(17

) 42

9(5)

42

7(5)

42

9(6)

42

7(6)

42

9(7)

42

7(7)

44

5(8)

44

3(3)

>

-

426(

28)

424(

10)

426(

21)

424(

28)

426(

21)

424(

11)

442(

32)

440(

14)

[A

[M - H

,01"

410(

21)

426(

40)

424(

51)

408(

5)

-

-

[M - H,O

- C

H,]

395(

9)

411(

30)

409(

37)

393(

6)

-

-

-

411(

12)

409(

7)

411(

12)

409(

10)

411(

13)

409(

6)

427(

16)

425(

16)

[A

[M -

2H,0

1+'

-

408(

4)

-

-

-

-

-

408(

10)

-

408(

4)

-

408(

8)

-

424(

23)

422(

6)

% 39

3(10

) -

409(

26)

407(

6)

2 [M

-2H

,0-C

H3]

' -

393(

10)

-

-

-

-

-

393(

11)

-

393(

7)

-

[M C

,H,Ol+

37

0(28

) 38

6(37

) 38

4(56

) -

-

-

-

386(

9)

384(

26)

386(

14)

384(

14)

386(

5)

384(

12)

-

400(

11)

rn R

[MI"

428(

39)

444(

43)

442(

41)

426(

82)

424(

61)

424(

69)

424(

52)

444(

27)

442(

13)

444(

27)

442(

8)

444(

44)

442(

33)

460(

23)

458(

5)

v)

n

[M - H

,O-C

,H,O

]" -

368(

21)

-

-

-

-

-

368(

14)

-

368(

19)

-

368(

2)

-

384(

54)

382(

58)

[M - H,

O C,H

,O-CH

,] '

-

353(

11)

-

-

-

-

-

353(

4)

-

353(

5)

-

353(

6)

-

369(

26)

367(

41)

a $

(C - H

ZO)

191 (

100)

20

7(97

) 20

5(56

) 20

7(57

) 20

5(25

) 20

5(62

) 20

5(75

) 20

7(89

) 20

5(34

) 20

7(78

) 20

5(40

) 19

1(10

0)

191 (

100)

20

7(93

) 20

5(70

) (a

- H

,O)

(6 -

H2

0)

189(

88)

189(

100)

18

9(87

) -

-

-

-

189(

100)

18

9(86

) 18

9(91

) 18

9(89

) 20

5(52

) g

205(

91)

205(

70)

C

231(

19)

247(

14)

245(

23)

247(

73)

245(

66)

245(

38)

245(

22)

247(

4)

245(

5)

247(

10)

245(

9)

231(

14)

f 24

7(10

) 24

5(9)

2

-

-

229(

13)

-

-

229(

12)

-

229(

48)

-

-

-

229(

16)

-

229(

6)

-

189(

72)

-

-

-

189(

100)

-

189(

91)

-

-

-

189(

90)

-

Z

149(

82)

149(

100)

14

9(10

0)

149(

100)

16

5(35

) 9

9 2

189(

100)

-

-

b 20

7(71

) 20

7(97

) 20

7(58

) 18

9(72

) 18

9(51

) 18

9(67

) 18

9(90

) 20

7(89

) 20

7(48

) 20

7(78

) 20

7(69

) 22

3(42

) g

223(

41)

223(

25)

3 C rn

(b C

XHG

O)

149(

98)

149(

99)

149(

100)

-

-

-

-

a e,

m/z

136

(10

0%).

[M

C,

H,]',

m/z

381

(10

0%).

C,,H

,,, m

/z 1

35 (

100%

).

C,H,,,

m/z

109

(10

0%).

(p

-H,O

), m

lz 1

51 (

100%

).

' m/z

231

corr

espo

nds

(k

No

t si

gnifi

cant

. H,

O)

as e

stab

lishe

d by

15b

.

J. SCHMIDT AND S. HUNECK

[MI+’, m/z 444

100

- s? - a, c U

a 5c a,

0 a, [L

._ c -

0

a, mlz 201 b, m/z 201 c, mlz 241

I-H.0 -H20 j A l - w w I-&. (a-H,O), m/z 189 (b-H,O), m/z 189 (b-C,H,O), m/z 149 (c-H,O), mle 229

Scheme 1. Skeletal fragmentation of 3p,22-dihydroxyhopane (2).

11 12

4: mlz 241 (73%) 5: mlz 245 (66%)

.1

(C -H,O), mlz 229 (48%)

,& _ I L d v e

R 0/+

4: R=@-OH, a-H 5: R = O 4: mlz 426 (82%) 5: m/Z 424 (61%) [MI’’, {

Scheme 2. Origin of the key ions c, d, e in 4 and 5.

4: 100% e, m/z 136[ 5: 95%

4: 53% d, mlz 150{ 5 : 38%

)O

rn / z

Figure 1. 10-16 eV mass spectrum of 3-0x0-22-hydroxyhopane (3).

n 9

(189

200 250 300 3 50 400 450

658 ORGANIC MASS SPECTROMETRY, VOL. 14, NO. 12, 1979 0 Heyden & Son Ltd, 1979

MASS SPECTROSCOPY OF NATURAL PRODUCTS-VI

'0°1

100

119

rn / z

Figure 2. 10-16eV mass spectrum of zeorinone (10).

I00

- s 8

5 50 n

- 0 u

._ P

d 0 c -

0

rn / z


\ "// 02 12

[MI", mlz 442 (&"lo) f, mlz 233 (36%) b, mlz 207 (69%)

i

h, m/z 207 (69%) g, mlz 220 (59Yo)

Scheme 3. General fragmentation of 7-0x0-22-hydroxyhopane (12).

@ Heyden & Son Ltd, 1979 ORGANIC MASS SPECTROMETRY, VOL. 14, NO. 12, 1979 659


15 [MI+', m/z 442 (33%)

k, mlz 249 (72%) 1, m/z 236 (30%) m, mlz 222 (24%)

Scheme 4. Origin of the key ions k, I , rn in 15-0x0-22-hydroxyhopane (15).

I001 I191 a

n

I, 11,. I, I1 14 1j1 . ,I! , I, , , . . , . 4 . 1 . I,,

"..-. 369

100 I50 200 250 300 350 400 4 50 m / z


I00

- - s 8

< 5 0 n

2

E

0

0

0 .- c -

0 I00 I 50 200 250 300 350 400 450

m/z

Figure 5. 1 c 1 6 e V mass spectrum of leucotylin (16).

660 ORGANIC MASS SPECTROMETRY, VOL. 14, NO. 12, 1979 @ Heyden & Son Ltd, 1979

MASS SPECTROSCOPY OF NATURAL PRODUCTS-VI

50 -

0 ,

100 1 [ M - 11- 1159

[M - >OH]- 101

[M-1- HzOl- L l I

213 232 L13

. , , I , , , , . , I , . I 1 , , , . , , , . , , , , . . . I , , , , I 1 , , c

m/z

Figure 6. 2 4 e V negative ion mass spectrum of leucotylin (16).

a hydroxy function, an 0x0 group is more suitable for its position to be identified in rings A, B (see Figs. 1-3), because (i) a-deuteration allows positions 3 and 7 to be distinguished from 6l" and (ii) the 7-0x0 group induces a characteristic fragmentation (Scheme 3) . The ions f, g and h probably arise via a hydrogen transfer from the ring C opened form. In 12b ions b and h5 are separated.

The mass spectra of the naturally occurring ring D substituted hopanes 13 and 16 show an ion b at m/z 223.7 However, the 15-0x0 derivative 15 (Fig. 4) displays specific fragments (Scheme 4, k, 1, m). In contrast to 15-oxoolean-12-enes" in 15 a hydrogen transfer from the charged species leading to the diag- nostically important ion k is observed. A possible

mfz 460 (23%)

m/z 445 (8%) * -HzO I I m/z 427 (16%) -H20

m/z 409 (26%)

mechanism is shown in Scheme 4. Ion b is not significant, but ion rn at m/z 222 formally corresponds to ( b + H). The mass spectrum of leucotylin (16) (Fig. 5 ) reveals consecutive substituent elimination and the key ions a, b and c. However, the appearance of significant ions p and (p -H,O) (Scheme 5 ) not shifted in the derivatives 17a and 18 is of special interest. The favoured origin of ion p can be explained by an a-cleavage at C-16. A similar fragmentation in 13 does not occur. Therefore, localization of an oxygenated substituent at C-15 or C-16 is possible by mass spectrometry.

The negative ion mass spectra of the hopanes investigated show very intense [M - 11- ions representing the base peak in most cases, and substituent elimina-

1 +.

COH '.

/'%, OH

16 [MI+', C J L 0 ,

* -HzO *

m/z 442 (32%) a, mlz 207 (93%)

* -H*O

n, m/z 330 (12%) I m/z 361 (11%)

m/z 351 (14%)

(a-H,O), m/z 189 (90%)

Scheme 5. Fragmentation of leucotylin (16).

*I L

b, mlz 223 (41%)

]-H@

/7 (b-H,O), m/z 205 (96%)

\-H& 4\cF OH

(b-2H20), m/z 187 (65%) \ + OH

p, m/z 169 (46%)

I-HKI

(p-H,O), m/z 151 (lOO?'o)

@ Heyden & Son Ltd, 1979 ORGANIC MASS SPECTROMETRY, VOL. 14, NO. 12, 1979 661

tion (Fig. 6). The skeletal fragmentation seems to be unspecific. In some cases ions above the molecular ion region appear, e.g. in the presence of double bonds.12 In general, the negative ion mass spectra of pentacyclic triterpenes yield only limited structural information compared with that of the positives ones.

EXPERIMENTAL

The positive (10-16 eV) and negative (2-4 eV) ion mass spectra were obtained from an electron attach- ment mass spectrograph of the Research Institute 'Manfred von Ardenne,' Dresden, GDR (unheated ion source, inlet temperature 100-150 "C, electron current 10 mA, accelerating voltage 40 kV, source pressure lop2 Torr, analyser pressure lo-' Torr). The low energy electrons were produced in a low pressure plasma (discharge gas argon).13 Accurate mass meas- urements were obtained from a JEOL JMS-D 100 mass spectrometer (electron energy 75 eV, resolving power about 10 000) using the 'peak matching


REFERENCES

method.' The direct analysis of daughter ion measure- m e n t ~ ' ~ of 16 were recorded on a Varian MAT 3 11A instrument.

All compounds used have been described in the literature and were obtained from natural sources or by standard preparations. The deuterium content of the corresponding derivatives was calculated by a pro- cedure described previ0us1y.l~

(a) LiAD-reduction of the ketone: 4a, 9a, l l a , 14a, 17a; 2% do, 98% d,.

(b) Base-catalysed exchange:" 3b, 12b, 15b; 4% do, 8% d, , 88% dZ, lob; 5 % do, 11% dl, 26% d,, 58% d3.

Acknowledgement

The authors are indebted to Dr W. Ihn, Central Institute for Microbiology and Experimental Therapy, Jena, GDR, for high resolution mass data and Dr G. Hofle, Technical University, Berlin (West), Institute of Organic Chemistry, for the direct analysis of daughter ion spectra of leucotylin.

1. H. Budzikiewicz, J. M. Wilscn and C. Djerassi, J. Am. Chem. SOC. 85, 3688 (1963).

2. H. Budzikiewicz, C. Djerassi and D. H. Williams, Structure Elucidation of Natural Products by Mass Spectrometry, Vol. 11, Chapt. 23 and references therein. Holden-Day, San Fran- cisco (1964).

3. C. R. Enzell, R. A. Appleton and I. Wahlberg, in Biochemical Applications of Mass Spectrometry, ed. by G. R. Waller, Chapt. 13 and references therein. Wiley-lnterscience, New York (1972).

4. R. E. Corbett and H. Young, J. Chem. SOC. C 1556 (1966). 5. R. E. Corbett and H. Young, J. Chem. SOC. C 1564 (1966). 6. (a) R. E. Corbett and S. D. Cumming, J. Chem. SOC. C, 955

(1971); (b) R. E. Corbett and A. L. Wilkins, Aust. J. Chem. 30, 2329 (1977).

7. 1. Yosioka, T. Nakanishi, M. Yarnaki and 1. Kitagawa, Chem. Pharm. Bull. 20, 487 (1972).

8. St. Pyrek and E. Baranovska, Pol. J. Chem. 52, 97 (1978).

9. M. N. Galbraith, C. J. Miller, J. W. L. Rawson, E. Ritchie, J. S. Shannon and W. C. Taylor, Aust. J. Chem. 18,226 (1965).

10. J. S. Shannon, Aust. J. Chem. 16, 683 (1963). 11. C. Djerassi, H. Budzikiewicz and J. M. Wilson, Tetrahedron

Lett. 263 (1962). 12. S. Huneck and R. Tummler, J. Prakt. Chem. 38, (310), 233

( 1968). 13. M. von Ardenne, K. Steinfelder and R. Tummler,

Elektronenanlagerungsmassenspektrographie organkcher Substanzen, p. 22, Springer-Verlag, Berlin (1971 1.

14. U. P. Schlunegger, Angew. Chem. 87, 731 (1975); Angew. Chern. Int. Ed. Engl. 14, 679 (1975).

15. K. Biernann, Mass Spectrometry Organic Chemical Applica- tion, Chapt. 5. McGraw-Hill, New York (1962).

Received 20 August 1979; accepted 3 September 1979

@ Heyden & Son Ltd, 1979

662 ORGANIC MASS SPECTROMETRY, VOL. 14, NO. 12, 1979 @ Heyden & Son Ltd, 197Y

mass spectroscopy of natural products. vi—localization of functional groups in the hopane skeleton

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