научная статья по теме SYNTHESIS AND PHARMACOLOGICAL STUDIES OF NEW PYRAZOLE ANALOGUES OF PODOPHYLLOTOXIN Химия

Текст научной статьи на тему «SYNTHESIS AND PHARMACOLOGICAL STUDIES OF NEW PYRAZOLE ANALOGUES OF PODOPHYLLOTOXIN»

SYNTHESIS AND PHARMACOLOGICAL STUDIES OF NEW PYRAZOLE ANALOGUES OF PODOPHYLLOTOXIN

© 2014 B. Umesha and Y. B. Basavaraju#

Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore — 570006, Karnataka, India

Received December 20, 2013; in final form February 10, 2014

The pyrazole analogues of podophyllotoxin were synthesized by the chalcone route. This route attracts the attention because of its simple operating conditions and easy availability of the chemicals. Initially, benzylide-neacetophenones (chalcones) were prepared in high yields by Claisen-Schmidt reaction of acetophenones with 4-(methylthio)benzaldehyde. The cyclopropyl ketones were prepared in good yields by the reaction of chalcones with trimethylsulfoxonium iodide. Tetralones were prepared in good yields by the Friedel-Craft's intramolecular cyclization reaction of cyclopropyle ketones in the presence of anhyd. stannic chloride and acetic anhydride. The tetralones on formylation to give substituted hydroxylmethylene tetralones. Condensation of substituted hydroxylmethylene tetralones with hydrazine hydrate afforded target compounds. The structures of the synthesized compounds were confirmed by IR, 1H-NMR and Mass spectral technique. The title compounds were screened for their antimitotic and antimicrobial activities. Among the synthesized compounds cyclopropyl ketones and pyrazole analogues of podophyllotoxin, compound 7-(Methylthio)-5-(4-(methylthio)phe-nyl)-4,5-dihydro-2#-benzo[g]indazole is more active than 5-(4-(Methylthio)phenyl)-4,5-dihydro-2#-ben-zo[g]indazole, 7-Methyl-5-(4-(methylthio)phenyl)-4,5-dihydro-2#-benzo[g]indazole, 7-Methoxy-5-(4-(meth-ylthio)phenyl)-4,5-dihydro-2#-benzo[g]indazole and the key intermediate tetralones in 100, 200 and 400 ppm at 12, 18 and 24 hrs and also showed very good activity against screened bacteria and fungi compared to their standard.

Keywords: acetophenones, chalcones, cyclopropylketones, tetralones, antimitotic activity, antimicrobial activity

DOI: 10.7868/S0132342314040137

INTRODUCTION

Podophyllotoxin (Fig. 1) is a most abundant naturally occurring antimitotic cyclolignan, derived from variety of plants, such as podophyllum peltalum, podo-phyllum emodi, podophyllum pleianthum, podophyllum hexandrum anthriscus sylvertris and juniperus Sabina [1—7]. Podophyllotoxin exhibits high antimitotic and apoptotic activity, this is due to its affinity for tubulin and mitotic spindles of dividing cells at metaphase. Since it is having high toxicity, it reduces the application of podophyllotoxin as an anticancer agent. The toxicity of podophyllotoxin liberates as diarrhea, nausea, vomiting and damages to the healthy tissues [8, 9]. At the same time heterocyclic ring systems have emerged as powerful scaffolds for many biological evaluations [10]. Heterocyclic compounds provide scaffolds on which pharmacophores can arrange to yield potent and selective drugs [11]. Pyra-zoles and their derivatives play an important role in medicinal chemistry research. Several derivatives of pyrazole are of pharmaceutical interest due to their analgesic power. Among them, derivatives of 5-isopy-

razolone and pyrazolidine-3,5-dione are worth noting due to their clinical interest. Several, substituted pyra-zolines are reported to possess moderate antibacterial and antifungal activities. Besides, a number of nitrofu-rylpyrazoline derivatives were found to possess antibacterial activity. Pyrazole molecules are also exhibit anticancer, anti-inflammatory, antidepressant, anticonvulsant [12]. The incorporation of pyrazole ring into the podophyllotoxin enhances the biological activities to a great extent and also presence of different

OH H^i H

H3CO

O

Hwl H o

OCH3 OCH3

# Corresponding author (tel.: +91 948 044-18-04; e-mail: basavaraju_yb@yahoo.co.in; umesha.basaviah54@gmail.com).

Fig. 1. Podophyllotoxin.

substituents on the new pyrazole analogues of podo-phyllotoxin, well improve the biological properties. Hence these modifications of its structure are required to reduce its toxicity and to enhance its biological activity. The biologically active and less cytotoxic new pyrazole analogues of podophyllotoxin have been synthesized.

RESULTS AND DISCUSSION

The synthesis of new pyrazole analogues of podo-phyllotoxin has been carried out by chalcone route (scheme). The benzylideneacetophenones (chalcones) (IIa—d) were prepared in high yields by Claisen-Schmidt reaction of acetophenones (Ia—d) with 4-(methyl-thio)benzaldehyde in the presence of sodium hydroxide in water-ethanol mixture [13, 14]. The structures of the chalcones were confirmed by IR and 1H NMR spectral studies. IR spectra of compounds (IIa—d) showed the C=C stretching frequency in the range 1667—1656 cm-1 and 1H NMR showed the absence of aldehyde proton at 9.83 ppm. The cyclopropyl ketones (IIIa-d) were prepared in good yields by the reaction of chalcones (IIa-d) with trimethylsulfoxonium iodide (TMSOI) in the presence of sodium hydride in dry DMSO [15, 16]. The sodium hydride acts as a base which abstracts a proton from the methyl group in tri-methylsulfoxonium iodide to form a dimethylsulfoxo-nium methylide. It attacks nucleophilically the P-car-

bom atom of the chalcone which acts as Michael receptors to form an enolate ion, which undergoes nucleophilic attack on the methylene carbon atom bearing the dimethylsulfoxonium cation intramolecu-larly finally to form the desired cyclopropyl ketone. The structure of compounds (IIIa-d) was confirmed by IR spectra. In its IR spectra exhibit C=O stretching band in the range 1687-1671 cm-1 and 1H NMR showed the cyclopropane CH and CH2 peak at the range 0.83-0.78 and 2.21-2.00 ppm respectively. Te-tralones (IVa-d) were prepared in good yields by the Friedel-Craft's intramolecular cyclization reaction of cyclopropyle ketones (IIIa-d) in the presence of an-hyd. stannic chloride and acetic anhydride in dry dichloromethane [17]. The cyclopropyl ketones undergo electrophilic ring opening in the presence of Lewis acid to give benzylcarbocationic intermediate which is intramolecularly attacked by aryl ring n-electrons resulting in the formation of a six membered ring with a pendant carbocation. This readily gives up proton to form tetralones. Acetic anhydride facilitates the formation of desired tetralones. In its IR spectra appeared absorption bands in the range 3133-2934 cm-1 and 1705-1685 cm-1 corresponds to aromatic C-H and C=O stretching frequencies and 1H NMR of the ring B proton appears in the range 2.65-2.18 ppm. They are key intermediates for the preparation of the new pyrazole linked podophyllotoxin analogues.

O^H

R

(Ia-d)

R'

SCH3

O

(IIa-d)

HCOOC2H5 NaH, dry C6H6, rt

SCH3 (IVa-d)

TMSOI

DMSO

O

R'

Ac2O, Anhyd. SnCl4 Dry CH2Cl2

SCH3

(IIIa-d)

SCH3 (Va-d)

SCH3

(VIa-d)

(Ia)-(VIa) R = H; (Ib)-(VIb) R = CH3; (Ic)-(VIc) R = OCH3; (Id)-(VId) R = SCH3 Scheme. Protocol for synthesis of tetralones (IVa-d).

Table 1. Antimitotic activity of the compounds (IVi-d) by onion root tip method

Comp. No.

Conc. in ppm

% Dividing cells

% Dividing cells compared to control

% Inhibition compared to control

ID50 in ppm

Time, hrs

12 18 24 12 18 24 12 18 24 12 18 24

Control - 32.91 24.72 21.74 100 0.0 -

(IVa) 100 22.24 20.03 14.50 67.57 81.02 66.69 32.43 18.98 33.31

200 19.91 17.02 13.23 60.49 68.85 60.35 39.51 31.15 39.15 380 390 400

400 15.85 11.99 10.77 48.16 48.50 49.54 51.84 51.50 50.46

(IVb) 100 19.02 17.18 17.01 57.79 69.49 78.24 42.21 30.51 21.76

200 17.47 12.01 13.13 53.08 48.58 60.39 46.92 51.42 39.61 320 190 370

400 15.51 10.00 10.56 47.12 40.45 48.57 52.88 59.55 51.43

(IVc) 100 19.99 18.48 15.45 60.74 74.75 71.06 39.26 25.25 28.94

200 16.66 15.56 13.00 50.63 62.94 59.79 49.37 37.06 40.21 220 350 350

300 14.56 11.45 10.01 44.24 46.31 46.04 55.76 53.69 53.96

(IVd) 100 17.56 13.01 13.20 53.35 52.62 60.71 46.65 47.38 39.29

200 15.69 09.56 09.21 45.85 39.88 42.36 54.15 60.12 57.64 140 120 160

400 11.78 07.09 05.45 35.79 28.68 25.06 64.21 71.32 74.94

The tetralones on formylation to give substituted hydroxylmethylene tetralones (Va-d) [18]. Formyla-tion of the presently synthesized tetralones with ethyl formate using sodium hydride as the base at room temperature gave single product in good yields. The P-di-carbonyl compounds which exist in the enol form show the carbonyl absorption in the region 1640-1610 cm-1. Generally 1,3-diketones absorption peak with high intensity appeared at 1715 cm-1. Enols containing this grouping, but the shift that occurs in these compounds is attributed to the intramolecular hydrogen bonding.

At the same time, the true alcoholic hydroxyl band near 3530 cm-1 is absent in enols, but there is a band near 3258-3251 cm-1 (s) which is attributed to the chelated hydroxyl group. 1H NMR showed the vinylic proton absorption at 5.80-5.60 ppm. The new pyra-zole analogues of podophyllotoxin (VIa-d) were synthesized in high yields by the condensation of hy-droxymethylene tetralones and hydrazine hydrate in absolute ethanol [19]. The products were puried by re-crystallization from ethanol. The compounds (VIa-d) exhibited NH stretching band at 3490-3360 cm-1 and proton NMR showed singlet NH peak at 12.64-12.55 ppm. Based on this, the structures of the synthesized compounds were confirmed.

Biological activities

Antimitotic activity

Allium cepa has been used to evaluate the antimitotic activity of new pyrazole analogues of podophyllotoxin. Root tip cells in (IVa-d) and (VIa-d) exhibited changes in cellular morphology such as slight elongation in shape with many of them remain in the

earliest stages of mitosis called prophase stage. Onion roots in compound (IVi-d) and (VIa-d) of 100, 200 and 400 ppm at 12, 18 and 24 hrs exhibited changes in chromosomes and shape of the cells with elongated appearance. Using cytotoxic nature of new pyrazole analogues of podophyllotoxin showed very less number of dividing cells. Change in chr

Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.

Показать целиком