Quantitative Structure Activity Relationships of 5-Nitrofuran Derivatives

B. M e s t e r I / N. Hikichi 2 / M. Hansz 2 / M. Paul ino de B lumenfe ld .2

1C~itedra de Qufmica Farmac6utica, Facultad de Qufmica, 1157, Montevideo, Uruguay 2C~itedra de Qufmica Cu~intica, Facultad de Qufmica, 1157, Montevideo, Uruguay

Key Words Column liquid chromatography Nitrofuran derivatives Structure-activity relationships

Summary Quantitative structure-activity relationships were per- formed on a set of 5-nitrofuran derivatives. The cor- relation parameters used were hydrophobicity and connectivity. The former was measured by means of the capacity factor (logko) obtained by HPLC and the

latter through the molecular valence connectivity index 1zv obtained by computational methods. The biological activity data considered were growth inhibition percentages of T. cruzi (GI % (48 h)) and half-maximal inhibitory concentration of Glutathione Reductase (i0.5 (max)). Good adjustment, r = 0.98, was obtained if a logarithmic model is used for I0.5 (max) correlations. When GI % is considered, correlations were poorer and the consideration of both structural parameters was necessary for their improvement, r = 0.94.

O =N ~.,O ~ N"- N/~'S Oz ) / HaO

]a

O ; z N ~ N~" R

Figure 1 R = b C

d e

f g h i J k I n l

n

pyrazol-l-yl imidazol-l-yl 1,2,4-triazol-4-yl 1,2,4-triazol-l-yl indol-l-yl indazol-l-yl benzimidazol-l-yl benzotriazol-l-yl 3,5-bis(methylthio)-l,2,4-triazol-4-yl 1-methyl-3-methylthio-l,2,4-triazol-4-yl-5-thione 1-mcthyl-3-mcthylthio-l,2,4-triazol-4-yl-5-one 4,6-diphenylpyridin-l-yl-2-one 3-thioxo-6-methyl-l,2,4-triazin-4-yl-5-one

Introduction Chagas disease or American trypanosomiasis affects 20 million people in Latin America. Today, Nifurt- imox (NFX, Figure 1) is one of the most important drugs in the treatment of the disease. Because of its partial efficiency and high toxicity a search of new agents has been undertaken. Our contribution to that field has been the study of a new series of N-[(5-nitro- furfurylidene) amino] azoles and azines (Figure 1) in their chemical, spectroscopical and biological pro- perties [1-3].

In the present work we have started the study of the quantitative structure-activity relationships (QSAR) of these compounds [4-6].

Nitrofurantoine, nitrofurazone and 2-nitrofuroic acid were used as representatives of molecules with non- planar heterocyclic residue.

We have chosen hydrophobicity and connectivity as structure-related parameters. The former is measured by means of the capacity factor, log k', obtained by HPLC [7, 8]. This parameter has proved to be propor- tional to log P (octanol-water partition coefficient) which is a widely used correlation variable for meas- uring hydrophobicity in QSAR. The connectivity is measured through the molecular valence connectivity index, 1)~v.

The biological activity data considered were growth inhibition percentages of T. cruz i after 48 hours of incubation (GI % (48 hs)) and half-maximal inhibitory concentration of Glutathione Reductase (I0.5 (max)), a mammalian enzyme involved in detoxification redox mechanisms [1, 9].

Chromatographia Vol. 30, No. 3/4, August 1990 Originals 191

0009-5893/90/8 0191-04 $ 03.00/0 �9 1990 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH

Materials and Methods

Materials C o m p o u n d l b - l h w e r e s y n t h e t i s i z e d as d e s c r i b e d by M e s t e r et al. [1]. N F X was p r o v i d e d by B a y e r A . G .

T h e b io log i ca l ac t iv i ty m e a s u r e m e n t s we re d e s c r i b e d e l s ewhere [1, 9].

H P L C - g r a d e m e t h a n o l was o b t a i n e d f rom E.M. Merck Co. a n d r e a g e n t g r a d e w a t e r was g e n e r a t e d by a M i l l i p o r e Mi l l i -Q | wa te r pu r i f i ca to r sys tem.

Chromatography H P L C was p e r f o r m e d on a W a t e r s | H P L C a p p a r a t u s cons i s t i ng of a M o d e l 600A so lven t d e l i v e r y s y s t e m and a M o d e l U 6 K injec tor . T h e c o m p o u n d s s t ud i e d in this e q u i p m e n t we re d e t e c t e d by a W a t e r s M o d e l 440 a b s o r b a n c e s p e c t r o p h o t o m e t r i c d e t e c t o r a t 254 rim. R e t e n t i o n d a t a were co l l ec ted by a W a t e r s M o d e l 730 D a t a M o d u l e at a ra te of 0.5 cm/min.

F o r ana lys i s a ~ t -Bondapack C18 c o l u m n was used at 25 ~ M o b i l e p h a s e s c o n s i s t e d o f m i x t u r e s o f m e t h a n o l - w a t e r a t 60, 70, 80, 90 and 100 % (v/v), at a f low ra te of 1 ml/min.

C o m p o u n d s l a - l h w e r e d i s s o l v e d in m e t h a n o l a t a c o n c e n t r a t i o n o f 1 gg /ml . T h e v o l u m e of s a m p l e i n j ec t ed was 5 pl. T h e e x p e r i m e n t s were ca r r i e d ou t t h r ee t imes and the m e a n va lue was cons idered .

C a l c u l a t i o n s

The r e t e n t i o n t ime can be expres sed as a funct ion of k ' , the capac i ty factor , as fol lows:

k' - tR - t~

t o

we re tR is the r e t e n t i o n t ime of the c o m p o u n d and to is

the r e t e n t i o n t ime of an u n r e t a i n e d s u b s t a n c e (po t - a s i u m iod ide ) .

T h e k ' v a l u e s c o r r e l a t e wi th t h e o r g a n i c s o l v e n t c o n c e n t r a t i o n by the fo l lowing e q u a t i o n [7]:

log k" = log k o + b" C

w h e r e l o g k o is the va lue of log k ' at z e ro m e t h a n o l

c o n c e n t r a t i o n , b " is a cons t an t and C is the m e t h a n o l c o n c e n t r a t i o n ( % , v/v).

F ina l ly , l og k o is a p a r a m e t e r r e l a t e d to h y d r o p h o b i c -

ity. In mos t cases t he re is a l inear r e l a t ionsh ip b e t w e e n l o g k o and log P [8], the f o r m e r be ing much eas i e r to

ca l cu l a t e .

M o l e c u l a r c o n n e c t i v i t y is a m e t h o d to q u a n t i f y the t o p o l o g i c a l s t r u c t u r e o f m o l e c u l e s d e s c r i b i n g the i r r a m i f i c a t i o n , i n s a t u r a t i o n , c y c l i z a t i o n and p r e s e n c e and ub iqu i ty of h e t e r o a t o m s [10-14]. T h e s e p r o p e r t i e s were a c c o u n t e d by the connec t iv i ty index, rn)c, a g r a p h t h e o r e t i c a l p a r a m e t e r w h i c h can b e e v a l u a t e d by s e v e r a l i n d e p e n d e n t f o r m u l a t i o n s . T h e s i m p l e s t v e r s i o n of this index , d e s i g n e d as 1)~ and k n o w n as f i r s t -o rde r connec t iv i ty index is c o m p u t e d as shown in [15]. The n a t u r e of the a t o m is no t c o n s i d e r e d in this ve r s ion .

T o a c c o u n t fo r the n a t u r e of t he a t o m a n d the i n sa tu ra t i on of b o n d s in Z te rms, Ha l l and Kie r [15, 16] p r o p o s e d the v a l e n c e m o l e c u l a r c o n n e c t i v i t y index , 12v. I ts f i r s t -o rde r ve rs ion is:

n

1 1)cv = Y. i , j

1 4

where atoms i and j are bonded, and

5~= v Z k - h k

Tab le I. H P L C p a r a m e t e r s of the s tud ied p roduc t s and of KI, the in ternal s t anda rd

Comp 60 % MeOH 80 % MeOH

tR log k'

6.61 0.258

22.10 0.914

9.93 0.497

11.33 0.571

6.35 0.216

13.58 0.668

8.40 0.400

2.40

70 % MeOH

tR I log k'

7.36 0.428

4.63 0.119

3.01 - 0.297

3.70 - 0.071

9.41 0.569

5.65 0.261

6.13 0.315

4.33 0.066

7.10 0.407

5.23 0.208

11.53 0.678

2.00

90 % MeOH

tR log k"

6.18 0.320

3.83 - 0.039

2.95 - 0.323

3.70 - 0.177

5.86 0.285

4.23 0.047

4.46 0.090

3.60 - 0.100

4.93 0.166

4.11 0.023

5.98 0.299

2.00

100 % MeOH log ko tR log k' tR log k'

la 3.63 - 0.089 2.86 - 0.367 2.45

lb 3.31 - 0.184 3.04 - 0.284 1.08

lc 2.86 - 0.367 2.82 - 0.387 - 0.08

1 d 3.08 - 0.268 2.94 - 0.328 0.52

if 4.06 0.013 3.31 - 0.184 2.52

lg 3.45 - 0.140 3.10 - 0.260 1.61

lh 3.55 -0.111 3.12 - 0.252 1.78

l i 3.18 - 0.229 2.99 - 0.305 1.00

lj 3.75 - 0.060 3.19 - 0.225 1.99

lk 3.46 - 0.137 3.12 - 0.252 1.37

11 3.98 0.004 3.22 - 0.215 2.72

KI 2.00 - 2.00 - -

192 Chromatographia Vol. 30, No. 3/4, August 1990 Originals

a n d Z [ r e p r e s e n t s t he n u m b e r o f v a l e n c e e l e c t r o n s o f

t h e k - t h a t o m and hk t h e n u m b e r of h y d r o g e n s a t t a c h e d

to it. S i n c e h a l o g e n a t o m s h a v e an i d e n t i c a l n u m b e r o f v a l e n c e e l e c t r o n s , t h i s d e s c r i p t i o n y i e l d s i d e n t i c a l v a l u e s o f 8 v. I t w a s t h e r e f o r e n e c e s s a r y to d e r i v e e m p i r i c a l v a l u e s o f 8 v by c a l i b r a t i n g t h e m to a p h y s i c a l p r o p e r t y . T h e m o l a r r e f r a c t i o n was c h o s e n fo r th is a s s i g n m e n t [16].

Results and Discussion H P L C p a r a m e t e r s f o r t h e p r o d u c t s a n d f o r K I

( i n t e r n a l s t a n d a r d ) , a r e p r e s e n t e d in T a b l e I.

T a b l e I I r e s u m e s t h e d a t a f o r t h e b i o l o g i c a l p a r a - m e t e r s , I0.5 (max) a n d G I % (48 hs ) a n d f o r t h e

s t r u c t u r a l p a r a m e t e r s - l o g k o a n d tZv - o f t h e s t u d i e d c o m p o u n d s .

t T a b l e II . V a l u e s o f o g k o, c o n n e c t i v i t y i n d e x ( tZv) , h a l f - m a x i m a l i n h i b i t o r y c o n c e n t r a t i o n o f G l u t a t h i o n e R e d u c t a s e (Io.5 (max)) a n d g r o w t h i n h i b i t i o n

p e r c e n t a g e o f T. cruzi a f t e r 48 h o u r s of i n c u b a t i o n at a c o n c e n t r a t i o n o f 2.5 laM ( G I % (48 h)) .

/

Comp tZv / GI (48 hs) Io.5 log ko (max) /

la 2.45 5.57 28.5 31.0

lb 1.08 3.99 17.8 2.1

ie _ 3.97 - 3.4

ld - 0.08 3.84 7.4 8.3

le 0.52 3.84 17.2 -

i f _ 5.53 - 1.5

lg 2.52 5.40 17.2 0.9

lh 1.61 5.40 21.4 1.5

1 i 1.78 4.94 3.5 -

l j 1.00 4.92 35.8 1.9

lk 1.37 4.96 19.7 1.3

11 1.99 4.96 34.6 -

lm 2.72 7.83 74.2 -

i n _ 4 . 9 1 - 2.4

nitrofurantoine - 4.40 - 4.1

nitrofurazone - 3.37 - 39.0

_ 2.53 - 65.0 2-nitrofuroic acid

T a b l e I I I . n i t r o f u r a n d e r i v a t i v e s and N i f u r t i m o x .

C o r r e l a t i o n of h y d r o p h o b i c p a r a m e t e r s and c o n n e c t i v i t y i n d e x in

I0.50 (max) = - 2.66 log k o + 6.27

In I0.50 (max) : - 0.7910g k o + 1.74 6

Io.5o (m=) = - 13.82 1Zv + 74.99 13

10.5o (max) = - 2.39 lxv + 14.01 9

In I0.50 (max) = - 0.79 1Xv + 4.53 10

GI % (48 h) = 10.22 logk o +2.07 11

GI % (48 h) = 11.11 logk o +7.19 10

In GI % (48 h) = 0.35 log k o + 2.43 10

GI % (48 h) = 14.03 lxv -45.77 11

GI % (48 h) = 14.21 17,v - 46.29 10

In GI % (48 h) = 0.43 1Xv + 0.79 10

GI % (48 h) = - 11.91 log k o + 21.57 lxv - 65.66 11

r s

0.51 5.15

0.93 0.78

0.98 0.13

0.81 4.90

0.84 0.91

0.89 0.21

0.69 6.41

0.69 7.19

0.60

0.91

0.91

0.77

0.94

F

0.36

11.55

35.33

7.92

6.98

13.62

2.54

2.39

0.32 1.19

3.27 18.40

3.48 16.64

0.20 4.39

6.16 13.87

correlation equations statistical terms

n

I0.50 (max) = 3.08 log k o + 2,07 7

6

Correlations between these parameters are presented in Table III.

A linear regression analysis was performed on Io.5 (max) of liver G R and logk o to obtain Eqs. (1)-(3) (Table

III). The most simple and direct corre la t ion corre- sponds to equat ion 1 which gave a poor adjustment. Considerable improvement was obtained by excluding the data of NFX (Eq. (2), Table III) whose deviation was explained by means of steric reasons. The bet ter correlation (Eq. (3)) was obtained by using In I0.5 (max) instead of I0.5 (max).

A similar situation was founded when I0.5 (max) of liver G R was correlated with the connectivity index (Eqs. (4 ) - (6) , Table III) . Fol lowing the same line of reasoning, a be t te r corre la t ion was obta ined when NFX, n i t ro furan to ine and 2-ni t rofuroic acid were excluded. These three compounds are the only ones that possess a non planar heterocycl ic residue. As before , the best correlat ion was obta ined by using I0.5 (max).

When considering the GI % (48 hs), Eqs. (7)-(13) were obtained. Using this new parameter, several new facts arose. First, NFX behaves like the other analogs. Eqs. (8) and (11) were not bet ter correlat ions than Eqs. (7) and (10) where NFX is included. Second, the correlation did not improve when a logarithmic mode was used (Eqs. (9) and (12)) and furthermore the value of F decreased sharply.

Being the available data sufficient for trying a multiple correlation, Eq. (13) was obtained. In this case, using logk o and 1)~v the correlation was improved.

Conclusions The correlat ions obtained using 10.5 (max) show that drug activity increases with l ipophilicity. This is attributed to a bet ter hidrophobic interaction with the enzymatic receptor. The same is observed for 1%v, a pa rame te r re la ted to the atomic s t ructure of the molecules, specifically to their bulk steric properties.

However, there are steric factors in the drug receptor interact ion that have not been considered and that surely can explain the different behaviour of NFX, n i t rofuranto ine and 2-nitrofuroic acid. Correlat ions should be improved by considering Van der Waals surfaces as structural parameters.

The be t te r adjustment obtained for the logarithmic model agrees well with the hypothesis of a normal distribution for the probabil i ty of the molecules to reach the binding site in the enzyme.

When considering the GI % (48 hs), correlations are worse and fail in considering steric reasons or when logarithmic model is used. In this case the biological

parameter considered was the result of a much more complex set of factors than the I0.5 (max) of liver GR in which only the inhibition of an enzyme was involved. This can be seen in Eq. (13): when several variables are considered at the same time, the resulting correla- tion is bet ter than those obtained by using only one of the variables. Bet ter correlations should be obtained when consider ing o ther s t ruc tura l pa ramete r s de- scribing, for example, proximity, resonance and steric effects.

Acknowledgements This work was par t ly suppor ted by the Swedish Agency for Research Coopera t ion with Developing Countries (SAREC).

We thank Inst i tuto de Quimica Medica (Consejo Super io r de Inves t igac iones Cientificas, Madr id , Spain), where H P L C measurements were per formed and Asuncion Lorenzo for technical assistance.

We are indebted to Dr. R. M. Claramunt ( U N E D , Spain) and to Dr. A. O. M. Stoppani ( C I B I E R G , Argentina) for valuable comments and suggestions.

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Received: May 30, 1990 Accepted: June 10,1990 A

194 Chromatographia Vol. 30, No. 3/4, August 1990 Originals