SYNTHESIS OF VINCA ALKALOIDS AND RELATED COMPOUNDS, XLIX*

AROMATIC S U B ST IT U E N T E F F E C T S IN T H E C-14 E P IM E R IZ A T IO N

Istv á n Mo l d v a i1, A ndrás Ve d r e s2, Csaba Sz á n t a y J r .3’4,

G á b o r T ó t h3 and C s a b a S z á n t a y 1,* *

( lCentral Research In stitu te fo r C hem istry o f the H ungarian A ca d em y o f Sciences, H -1525 B udapest, P O B 17, *Chemical W orks o f Gedeon R ichter L td ., H -1475 B u d a p est, P O B 17, t e c h n i ­ cal A nalitical Research Group o f the H u n g a ria n A cadem y o f Sciences, Technical U niversity,

H - l l l l B udapest, Gellért tér 4, i On leave fro m Gedeon R ichter L td .) R eceived June 1, 1989

A ccepted for publication August 17, 1989

Some A-ring su b stitu ted vincam ine derivatives and their C-14 epim ers have been prepared and the arom atic su b stitu en t effects on the epim eric equilibrium o f these compounds in vestigated .

W e have reported th a t th e ( — )-14-epivincam ine (1) ^ (-f-)-vin cam in e (2) equilibrium can be in flu en ced b y m etal ions [2], and it w as fo u n d th a t 2 is therm odynam ically m ore sta b le th a n its C-14 epim er in th e n atu ral cis series [3],

W hile in vestigatin g stru ctu re-b io a ctiv ity relationships in th e V inca alkaloid field, the in flu en ce o f arom atic substituents on th e a b o v e equilibrium was studied.

M aterials

For th e preparation o f differen t nitrovincam ines ( + )-v in ca m in e (2) was nitrated [4]. When the separation o f th e tw o resultant regioisom ers (3 and 5) was carried out in an aceton e/w ater m ixture instead o f m eth a n o l [4 ], the form ation o f their C-14 epim ers could be detected by tic. O therw ise th e epi­

mers were prepared b y reflu x in g th e A-ring substituted vin ca m in e d eriv a tiv es in m ethanol in the presence o f aqueous am m onium hyd roxid e so lu tio n fo l­

low ed by separation using colu m n chrom atography (Schem e 1).

A t elevated tem perature (40 °C) th e nitration o f (-j-)-v in ca m in e vield ed tw o major com ponents. A fter work-up (-}-)-9 ,ll-d in itr o v in c a m in e (9) and

* For Part X L V III, see R ef. [1].

** To whom correspondence should be addressed.

A c ta C h im . H u n e . 1 2 8 , 1991 A k a d é m ia i K ia d ó , B u d a p e st

110 MOLDVAI et al.: VINCA ALKALOIDS, X L IX

3 R 1 = H R 2 r N 0 2 U

5 R 1 = ^{n o}2 R 2 = H 6

7 R 1 = H R 2 = Br 8

2 R , = H R 2 = H 1

Scheme 1

( — )-9 ,ll-d in itr o -1 4 -e p iv in c a m in e (10) were isolated* proving th a t epimeri- zation had occurred under th e given conditions. B o th epim ers afforded (+ )-9 ,ll-d in itr o a p o v in c a m in e (11) after elim ination o f water. N itration o f a m ixture o f 3 and 5 at 40 CC also yield ed dinitro com pounds (9 and 10) (Figure 1).

In XH nmr spectra th e chem ical sh ifts o f th e C15-H2 protons were a u th o rita tiv e. The difference in th e shifts o f these protons w as m inim al in th e case o f th e vin ca m in e d erivatives. On th e other hand, th is difference was considerable in th e C-14 epim ers (see: E xp erim en tal). T he 13C nmr chem ical sh ifts are collected in Table I and in F ig. 1 for 11. The interpretation o f the data o f n on -su b stitu ed derivatives w as published earlier [5]. The and 13C signal assignm ents o f com pound 11 were supported b y detailed nmr measure­

m en ts. The tw o-dim ension al carbon-proton correlation m ap o f 11 (Fig. 2a) allow ed th e assignm ent o f all CH units w ith th e ex cep tion o f th e H-10/C(10) and H -12/C(12) pairs. A p p lyin g th e sem iselective IN E P T (IN A P T ) [6] tech ­ nique op tim ized for J = 7 H z and J = 3 H z C-H couplings, resp ectively, a correlation b etw een the proton appearing at 8 8.45 and C(2) (134.8 ppm) w as o b tain ed . I t follow s th a t th e signals at 8.45 and 8.73 correspond to H-12 and H -10, resp ectiv ely . A series o f IN A P T m easurem ents on H -15, H -12, H -10 and H -3 gave unam biguous assignm ents o f signals C(14) and C(8), further o f C(9), C ( ll) and C(13) (F ig. 2b).

* Compound 9 was prepared earlier — Zsadon, B.: personal com m unication.

A cta C him . H u n g. 128, 1991

25

MOLDVAI et al.: VINCA ALKALOIDS, X L IX 111

Table I

I3C nm r spectra o f compounds 3 —10 (Chemical shifts, ő, in ppm , relative to TMS)

Carbon 3a 4* 5» 6b 7» 8* *b 10b

2 132.6 133.1« 136.4° 137.6° 132.2 132.6 134.9 136.9

3 59.1 58.9 59.5 59.0 59.1 58.8 58.9 58.8

5 50.4 50.4 51.2 50.7 50.8 51.0 49.7 50.0

6 16.4 16.2 19.7 19.2 16.7 16.6 18.7 18.5

7 107.0 107.4 105.6 104.4 106.1 106.6 105.9 106.3

8 133.6 134.6° 121.9 120.7 127.9 127.6 124.2 124.0

9 117.9 117.5 141.9 141.1 119.5 119.3 139.7 139.2

10 116.0 115.6 116.2 117.3 123.5 123.5 112.3 112.3

11 142.5 142.2 120.2 120.5 115.0 115.1 143.8 144.4

12 107.2 109.9 118.1 119.5 113.5 115.4 112.7 114.6

13 138.4 138.4 136.6° 138.3° 134.9 136.5 139.2 139.0

14 82.2 83.9 82.1 84.2 82.0 83.2 83.0 84.8

15 44.6 46.2 44.6 45.2 44.5 47.2 42.8 44.1

16 35.0 36.4 34.9 35.7 35.1 36.5 34.2 35.3

17 25.1 24.2 25.1 24.2 25.1 24.4 24.9 24.3

18 20.5 20.4 20.6 20.4 20.8 20.8 20.0 19.9

19 44.3 44.7 44.8 44.5 44.5 44.8 44.1 44.4

20 28.7 28.6 28.8 28.2 28.9 29.0 27.8 27.7

21 7.5 7.4 7.5 7.5 7.6 7.6 7.0 7.0

COOCH3 ^{54.5 53.4 54.5 53.1 54.5 53.6 53.4} 53.0

COOCH3 ^{173.2 170.9 173.9 170.7 174.0 172.3 171.2} 169.8

Solvents: a) CDC13; b) DMSO-dc;_c) ten tative assignment

2 or

3*5 A0*C

M e q H 4S03H

F ig. 1. Form ation o f dinitro derivatives. The 13C chem ical shifts of com pounds 11 (CDCL3, <5, in ppm . relative to TMS)

Acta C him . H un g . 128, 1991

1 1 2 MOLDVAI « al.: VINCA ALKALOIDS, X L IX

MeOOC

o<b

O

iL. i x J

PPM

F ig. 2a. T w o-dim ensional carbon-proton correlation m ap o f com pound 11

Epim erization

In order to esta b lish th e effect o f arom atic su b stitu tio n on the C-14 epim erization o f vin ca m in e d erivatives, th e equilibrium c o n sta n ts were deter­

m ined. The equilibrium con stan ts were m easured in all cases b y th e quanti­

ta tiv e u v -tlc densitom etric m ethod. In th e cases o f th e 1 ^ 2 and 8 [7] 7 [8 equilibria th e reaction rates are low , thus these equilibriu m constan ts were determ ined from th e rate con stan ts (see: E xp erim en tal). T h e com positions of

Acta Chim . H un g . 128, 1991

27

MOLDVAI et ai.: VINCA ALKALOIDS, X L IX 1 1 3

13

/

11 9

H-3

19 16 17 20

H-10

11 2 8

COO 14

H—12

16 2 0

H-15

i ' !NApT, Joc. _{* — o c} r 7 Hz

O.N

L it

\i

^{V ¡}

!

160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10

PPM

Fig. 2b. IN A P T m easurements for com pounds 11 8

1 1 4 MOLDVAI et al.: VINCA ALKALOIDS. X L IX

* Determined from th e rate constants; approximate values.

From these d a ta one can conclude th a t th e equilibrium constants

Hammett relationships fo r A -rin g substitued vincam ine/epivincam ine derivatives

R K

2 9

MOLDVAI et «1.: VINCA ALKALOIDS, X L IX 115

V 4

B

F ig. 4. S ta b ility relation of vincam ine/epivincam ine d erivatives

as a contribution to th e double bond — no bond form o f th e resonance hybrid (Fig. 4, B ). C on sequ en tly, th e orientation o f the h y d r o x y l group is essential.

In the case o f th e 1 4-ep ivin cam in e derivatives th e d elo ca liza tio n effect cannot operate because o f la ck o f th e appropriate steric o rien ta tio n o f th e hydroxyl group.

On th e basis o f th e above reasoning th e su b stitu e n t e ffe c ts can also be explained. E lectron -w ith d raw in g effects decrease th e jr-electron d en sity of the indole nucleus, th u s hindering th e form ation o f th e “ secon d ary bond” . Thus, the more and th e stronger electron-w ithdraw ing groups are attached to the A-ring, th e less w ill be the difference in s ta b ility b etw een th e tw o epimers.

As for th e m echan ism o f th e epim erization an ex p la n a tio n m ay be the following: rin g-opening occurs through a b a se-catalyzed h e ter o ly tic cleavage o f the N j— C14 b ond o f th e neutral m olecule, thus m akin g th e ro ta tio n possible, providing both epim ers on recyclization (Schem e 2).

Experimental

For preparative colum n chrom atography Merck K ieselgel 60 w as used . The optical rotations were m easured in chloroform at 25 i 2 °C. Ir spectra were recorded on a Specord IR 75 spectrom eter in K B r p elletts. The u v absorption spectra were recorded on a UV-VTS spectrometer; the spectra were measured in ethanol. Nmr spectra were ob tain ed on JEO L FX -100 and B R U K E R AC-250 instrum ents in CDC1?, CD3OD and DMSO-d,, solutions with TMS as internal reference. Chemical shifts are expressed in d u n its (pp m . downfield from TMS) and coupling con stants ( J ) are given in Hertz (H z). Mass spectra were tak en on an A EI-

MS-902 (70 eV, direct in sertion) m ass spectrometer. M.p.’s are uncorrected.

8* A cta C him . H u n e. 128. 1991

1 1 6 MOLDVAI e t ai.: VINCA ALKALOIDS. X LIX

Preparation o f th e dinitro deriratives

( -^)-9 ,1 1 -Dinitro vincamine (9 ) and ( — ) - 9 .11-dinitro-14-epivincam ine (1 0 )

To a solution o f a m ixture o f 9- and 11-nitrovincam ine (3 and 5, in a ratio o f about 1 : 1; 10 g; 25 m m ol) in glacial acetic acid (100 m L), fum ing nitric acid (40 m L; d — 1.52) d issolved in glacial acetic acid (40 m L ) w as added dropwise at 40 °C. The m ixture w as poured o n to broken ice (800 g) and m ethylene chloride (200 m L) was added. The m ixture was made alkaline (pH 8) by adding conc. aqueous am m onium hydroxide solution (270 m L). The organic layer w as separated and the aqueous phase w as extracted w ith m ethylene chloride (2 X 150 m L).

T he com bined organic phase was w ashed w ith w ater (3 X 100 mL) and dried ( N a .S 0 4). The filtrate w as evaporated in vacuum and th e residue (11 g) chromatographed on silica (500 g;

eluent: 2000 m L o f a m ixture o f eth y l acetate: cyclohexane 3/7). In this w ay tw o major frac­

tion s were separated. The com ponent h avin g th e larger retention factor was com pound 9 (5.3 g; 48% ). M.p. 170 — 179 °C (from diisopropvl ether). [a]p + 141.1° (c = 0.2).

Ir (K Br): 3450. 1740. 1530 c m - 1 . U v (E tO H ): 212. 314. 394 nm.

Ms (70 cV, 170 °C, m/s (% )): 444 (90. :U +), 443 (60), 426 (2), 398 (14). 385 (18), 384 (35), 383 (30). 374 (2), 367 (15). 357 (30), 342 (100. M -102), 327 (30), 314 (10).

»H nmr (CDC1,), d: 1.05 (3H , t. - C H .C H ,) ; 2.34 (1H , d, J = 14.6 Hz. 15-H); 2.50 (1H , d, J = 14.6 Hz. C15-H): 3.90 (1 H , s, - C O O C ii,); 4.10 (1H , s, C3-H); 8.78 (1H , d, C10-H ); 8.55 (1H . d. C12-I1); 1 . 3 - 3 . 4 (m , sk eletal + - C t f ;CH3).

18C nmr: see Table I.

C:1HJ4N40 7 (444.43). Calcd. C 56.75; H 5.44; N 12.60. Found C 56.70; H 5.39; N 12.65% . The com ponent w ith the sm aller reten tion factor was compound 10 (2.0 g; 18%).

M.p. 141— 144 °C (from acetone). [a ]o — 107.8° (c = 0.2).

Ir (K Br): 3450, 1750, 1510 c m -1 . U v (E tO H ): 213, 313, 392 nm.

Ms (70 eV, 170 °C, m/s (% )): 445 (23). 444 (82. M + ), 443 (52), 429 (15). 427 (23). 426 (5), 415 (14), 401 (16), 398 (11), 397 (12). 385 (20). 384 (36). 383 (36), 367 (16), 357 (30), 342 (100, m -102), 327 (31), 325 (16).

*H nmr (CDCl,), <5: 1.05 (3H , t, - C H .C H ,) ; 2.21 (1H , d, J = 14.6 H z. C15-H); 2.99 (1 H , d, J = 14.6 H z, C15-H); 3.84 (1H . s, - COOCJ/,); 4.10 (1H , s, C3-H); 8.79 (1H , d. C10-H);

8.69 (1H , d, C12-H); 1 . 3 - 3 . 4 (m , skeletal - - C i f .C H ,) .

C21H 24N40 ? (444.43). Calcd. C 56.75; 11 5.44; N 12.60. Found C 56.81; H 5.39: 1\~ 12.54% .

A cta Chim . H un g . 128, 1991

31 was evaporated to dryness under reduced pressure. The residue was crystallized from m ethanol (10 mL) to afford 11 (0.52 g; 61% ). M .p. 1 9 0 - 1 9 3 °C. [a]D + 279.8° (c = 0.2).

1 1 8 MOLDVAI t t al.: VINCA ALKALOIDS, X L IX

Determ ination o f the equilibrium and rate constants

The equilibrium and rate constants were determ ined b y m eans o f a H igh-Spead Chro- m ato Scanner (Shim adzu CS-920) using Merck TLC (Art. 5553) p lates. The tic spots were tak en at 20 m m distances. The scan param eters were: X = 12 m m ; Y = 15 mm: linearizer = 1.

The m easuring w ave-lengths were 388 nm for 3 and 4, 390 nm for 5 and 6, 282 nm for 7 and 8, 392 nm for 9 and 10, and 279 nm for 1 and 2.

Concentrations were determ ined from th e peak area data using external standards (pure epim ers 1— 10, resp ectively, spotted ju st after dissolving).

For th e determ ination o f th e equilibrium and rate con stants m ethan olic solutions (5 • 10-3 m ol/L ) were used at 25 ± 1 °C. Of these solutions 2 /jL was applied on to th e tic plates.

The concentrations were measured at different tim es, u n til no change was observed.

The com position o f the equilibrium state was established from the last m easurem ent.

For 1 2 and 7 “ 8 the com position o f the equilibrium state was established from th e equilibrium constant th a t w as determ ined from the rate con stants. The rate constants were calculated b y m eans o f a sim ple first-order equation: In (o 0 — x) — In a„ = —kt. Thus th e rate constants are [1/h]: /cj_. = 3.06 • 10 -3 , k t_rl = 9.58 • 1 0 ~ 5, k = 1.41 • 10-3 , i ^ 8 = 1 .1 1 -1 0 - « .

The authors are grateful to Dr. J. Tam ás and Dr. M. Mák for th e m ass spectrom etic m easurem ent, to Dr. A. N em es (R ichter Gedeon L td.) for com pound 1, and to Mrs. K. Welker for technical assistance.

R E F E R E N C E S

[1] S zántay, Cs., B ölcskei, H .. Gács-Baitz. E.: Tetrahedron, 46, 1711 (1990) [2] S zán tay, Cs., Szabó, L ., K alaus, Gy.: Tetrahedron, 33, 1803 (1977)

[3] K alaus, G y., G yulai, Zs., K ajtár-Peredy, M., G yőry, P ., Szabó, L ., Szán tay, Cs.: Acta Chim. A cad. Sci. H ung. 105, 221 (1980)

[4] Sarlet, P ., H annart, J.: Bull. Soc. Chim. B e lg ., 88, 93 (1979)

[5] (a) Bom bardelli, E ., B on ati, A .. G abetta, B ., Martinelli, E . M., M ustich, G., D anieli, B.:

F itoterapia, 2, 51 (1975); (b) see R ef. [2]

[6] B a x , A .: J. Magn. R eson ., 57, 314 (1984)

[7] Ger. O ffen.. 2.928.187 (R ichter Gedeon L td.); Chem. A bstr., 93, 95475 (1980) [8] B elg. P at. 823.409 (Sandoz); Chem. A b str., 84, 5229 (1976)

[9] E .g.: Carey, F. A ., Sundberg, R . J.: A dvanced Chemistry, Part A , p. 98. Plenum Press, N ew -Y ork —London 1978

Acta Chim. H ung. 128, 1991

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H.C. van der Plas, M. S im o n y i, F.C. A ld e rw e ire ld t. J .A . Lepoivre (E d ito rs ), 165

Bio-Organic Heterocycles 1986 — Synthesis. Mechanisms and Bioactivity. Proceedings o f the

4 th FE C H E M C onference on H eterocycies in B io-O rganic C hem istry. H outhalen , B elgium , 2 5 —28 May 1986.

© 1986 Elsevier Science Publishers B .V .. A m sterdam — P rinte d in The N etherlands

NITRO APOVINCAMINIC ACID DERIVATIVES: PREPARATION A ND BIOLOGICAL EFFECTS

1 1 1 2

A. VEDRES , I. MOLDVAI , B. STEFKO , and Cs. SZANTAY

^ Chemical Works of Gedeon Richter Ltd., Budapest, POB 27, H-14 75, (Hungary)

2 Central Research Institute for Chemistry of the Hungarian Academy of Sciences, Budapest POB 17, H-1525, (Hungary)

PREPARATION

As reported in the literature (ref.l) nitration of vincamine (la) results in a mixture of isomeric nitrovincamines lb and I c .

While 11-nitrovincamine (_Ic) can be separated by crystallization, the 9-nitro-isomer (_Ib) is isolated from the mother liquor by column chromatography.

We wish to report our recent findings on the investigation of nitration of vincamine (_Ia) as well as of the apovincaminic acid derivatives, Ila, lib.

Ia R=H (vincamine) Ila R=H (apovincaminic acid) lb R = 9 - N 0 2 lib R=ethyl (v i n p o c e t i n * )

Ic R = 1 1-N02

Manufactured by Gedeon Richter L t d . , Hungary

166

The ratio of the isomeric 9/11-nitro compounds was determined in the crude product. As shown (see Table 1), the ratio of isomers depended on the substrate. In case of vincamine (la) the formation of 9-nitro-isomer (lb was found to be poor, while nitrating apo- vincaminic acid derivatives, Ila and l i b , the 9-nitro compounds

(Ilia and IIIc respectively) were obtained in higher proportion.

These results indicate some steric hidrance of the nitration at position 11 in case of Ila and l i b .

TABLE 1

The ratio of the isoireric 9/11 nitro compounds in the crude product p r e p a r e d in acetic acid with nitric acid at 16°.

Substrate 9-isomer

(in %)

11-isomer

Vincamine (la) 28 72

Ethyl apovincaminate (lib ) 4 7 53

Apovincaminic acid 'Ila) 46 54

The isomeric nitroapovincaminic acids were preferably separe- ted by crystallization of the corresponding nitrate salts (ref.2).

The apovincaminic acid ester derivatives (III type c o m p o u n d s ) were prep a r e d in different ways; from compounds. I l i a , Illb by direct esterification, or by alkylation with alkyl sulphate or halides, or via the reaction of nitroapovincaminic acid halides with alcohols, or finally by transestérification of the methyl- esters of I l i a , Illb ref. 3!.

Ilia 9-N02 R=H

Illb 11-N02 R=H

IIIc 9 - N 0 2 R-ethyl

H i d i i-n o2 R=ethyl

H i e 9-N 0 2 R=n-propyl

Illf 9-N02 R=n-octyl

Ilia 9-N02

R=2-acetoxy-ethyl

3 5

BIOLOGICAL EFFECTS

The III type derivatives have shown valuable therapeutic properties, namely vasodilatory spasmolytic and antihypoxic effects.

The vasodilatory effect was studied in anaesthesized dogs.

Electromagnetic flow meters were used for measuring the blood flow in the femoral and internal carotid artery. Data are shown in Table 2.

TABLE 2

Circulatory effects (change in %) at intravenous doses of 1 mg/kg body weight.

167

Compound Carotid artery

flow

Femoral flow

lib + 30 + 15

IIIc +95 0

Illd + 10 0

Illf 0 0

The spasmolytic activity of the compounds was determined on isolated guinea pig ileum. The results are summarized in Table 3.

TABLE 3

Inhibition of barium chloride induced contraction of guinea pig ileum

Compound relative activity E D5^q

papaverine 1 . 0 5.4

l i b 2.7 2 . 0

IIIc 5.4 1 . 0

III g 13.5 0.4

H i e 27.0 o ^{• CM}

The antihypoxic activity was measured on conscious mice under normobaric hypoxia. The compounds were intraperitoneally

administered in a dose of 50 ug/kg (see Table 4).

168

TABLE 4

The antihypoxic effect on conscious mice under normobaric hypoxia

Compound Time of survival

min.

Increase of survival in %

control 6.0 + 1.0

-la 6.1 + 1.3 2

IIIc 13.4 + 2.4 123

IIIcj 10.1 + 3.5 68

H i d 11.0 + 3.4 83

CONCLUSION

On the basis of the above investigations it can be stated that the biological activity of vincamine derivatives is prefer­

ably influenced by substitution with a nitro group at ring "A".

The 9-nitro-derivative proved to be more active than the 11- nitroisomer. The cerebral vasodilating effects decreased when long chain alkyl esters were introduced. The Ille propyl ester has the highest antispasmolytic activity.

ACKNOWLEDGEMENT

We wish to thank our pharmacologist-coworkers, Drs. L. Szporny, E. Kárpáti, É. Pálosi, Zs. Szombathelyi and M. Riesz for their work and results.

REFERENCES

1 P. Sarlet and J. Hannart: Nitration de la Vincamine et de la Vincamone; Bull. Soc. Chim. Bela. 8_8 (1979 ) 93.

2 Spanish patent: 545 115; A. Vedres, Cs. Szántay, I. Moldvai and B. Stefkó: 9 or 11-substituted Apovincaminic Acid

Derivatives and Process for their Preperation; Spanish Patent 545 115

3 A. Vedres, Cs. Szántay, I. Moldvai, B. Stefkó, L. Szporny, E. Kárpáti, £. Pálosi, 2s. Szombathelyi, B. Kiss and M. Riesz:

Nitroapovincaminic Acid Derivatives; Spanish P atent 545 117

37

Journal of Molecular Structure, 212 (1989) 271-280 271

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In document EBURNÁNVÁZAS ALKALOIDOK ÉS SZÁRMAZÉKAIK ELŐÁLLÍTÁSA (Pldal 30-44)