SYNTHESIS OF NOVEL 1, 5-DIHYDROBENZOTHIAZEPINE DERIVATIVES BY CONVENTIONAL AND MICROWAVE IRRADIATION METHODS AND THEIR PHARMACOLOGICAL ACTIVITIES

Received on 11 September, 2013; received in revised form, 17 October, 2013; accepted, 09 January, 2014; published 01 February, 2014

SYNTHESIS OF NOVEL 1, 5-DIHYDROBENZOTHIAZEPINE DERIVATIVES BY CONVENTIONAL AND MICROWAVE IRRADIATION METHODS AND THEIR PHARMACOLOGICAL ACTIVITIES

Venkata Rao Vutla*¹, Rajendra Prasad Yejella ² andRamarao Nadendla ¹    

Department of Pharmaceutical Chemistry, Chalapathi Institute of Pharmaceutical Sciences ¹, Lam, Guntur, Andhra Pradesh, India

Department of Pharmaceutical Chemistry, University College of Pharmaceutical Sciences , Andhra University ², Visakhapatnam, Andhra Pradesh, India

ABSTRACT: 1, 5-Dihydrobenzothiazepines are synthesized by conventional and microwave assisted synthesis methods. By microwave assisted synthesis, a considerable increase in the reaction rate has been observed and that too, with better yields. The compounds have been screened for antimicrobial and cytotoxic activity. 1, 5-Dihydrobenzothiazepines are prepared by the reaction of 1, 3-diarylprop-2-enones with o-aminothiophenol. All the products were tested for purity by tlc and characterized by elemental analysis, IR, ¹H-NMR, ¹³C-NMR and mass spectral studies.

4-Fluoroacetophenone, 1, 5-DihydroBenzothiazepine, 2-Aminothiophenol, piperidine, microwave irradiation

INTRODUCTION:The 1, 5-benzothiazepines ¹ (1and 2) are important nitrogen- and sulfur-containing seven-membered heterocyclic compounds in drug research since they possess diverse bioactivities ^2-9.

1,5-Benzothiazepines are the most well-known representatives of benzologs of 1, 4-thiazepine (3) and one of the three possible benzo-condensed derivatives, viz. 1, 4-(4), 4,1- (5) and 1, 5-benzothiazepines ^10-13.

GENERAL STRUCTURES OF 1, 5-BENZOTHIAZEPINE

The 1, 5-benzothiazepine derivatives are of particular interest for lead discovery because they have been found active against different families of targets ^14-24. The first molecule of 1, 5-benzothiazepine used clinically was diltiazem (6), followed by clentiazem (7), for their cardiovascular action. Some of the 1, 5-benzothiazepine derivatives were also used clinically for CNS disorders which includes thiazesim (8), clothiapine (9) and quetiapine (10). Therefore, the 1,5-Dihydrobenzothiazepines are useful compounds in the drug research which has stimulated the invention of a wide range of synthetic methods for their preparation and chemical transformations ^25-45.

Microwave-induced organic reaction enhancement (MORE) chemistry is gaining popularity as a non-conventional technique for rapid organic synthesis. Important features of this technique are easy access to very high temperature, good control over energy input in a reaction; higher yields and rapid synthesis of organic compounds. The synthesized compounds were purified by recrystallization and chromatography. The compounds were characterized by 1H NMR and IR analysis. The compounds were tested for their antimicrobial and cytotoxic activity by standard methods.

MATERIALS AND METHODS: All the chemicals used in the work were of analytical grade and procured from sigma Aldrich, Visakhapatnam.

a)      General procedure for synthesis of 1, 5-benzothiazepines (BP-1-20): To a solution of chalcone derivative in dry acidic methanol acidified by adding few drops of glacial acetic acid to it, 2-aminothiophenol was added. The mixture was then refluxed until a crystalline solid separates out. After cooling, the solid product was collected and washed with diethyl ether and cold methanol. The crude solid was recrystallized from ethanol.

SCHEME-1: (BP-1-20)

b)      General procedure for synthesis of 1, 5-benzothiazepines (BP-1-20) by Microwave irradiation method: Equimolar quantities (0.001 mol) of chalcone derivatives and 2-aminothiopheno (0.001 mol) were mixed and dissolved in minimum amount (3 ml) of glacial acetic acid l. To this, piperidine (0.003 mol) was added slowly and mixed. The entire reaction mixture was microwave irradiated for about 2–6 min at 180 watts.Physical characterization data and Elemental Analysis dataof 1, 5-benzothiazepines were represented in table1 and 2.

TABLE 1: PHYSICAL CHARACTERIZATION DATA OF 1, 5-BENZOTHIAZEPINES (BP₁-BP₂₀)

Compound	R	Molecular Formula	Relative MolecularMass (RMM)	Melting Point (oC)	Yield%
BP1	C22H18FNS	347.45	141-143	89
BP2	C21H15F2NS	351.41	152-154	89
BP3	C21H15ClFNS	367.87	144-145	93
BP4	C21H15ClFNS	367.87	121-123	71
BP5	C21H14F3NS	369.40	139-141	75
BP6	C21H14Cl2FNS	402.31	118-120	86
BP7	C21H14ClFN2O2S	412.86	165-167	77
BP8	C21H15FN2O2S	378.42	143-145	82
BP9	C21H15FN2O2S	378.42	129-131	89
BP10	C21H16FNOS	349.42	227-229	84
BP11	C22H17FN2O2S	392.45	177-179	94
BP12	C24H22FNO3S	423.50	149-151	85
BP13	C22H16FNO2S	377.43	155-157	74
BP14	C19H13BrFNOS	402.28	133-135	79
BP15	C23H21FN2S	376.49	115-117	88
BP16	C22H18FNO2S	379.45	152-154	86
BP17	C20H15FN2S	334.41	112-114	78
BP18	C20H15FN2S	334.41	119-121	82
BP19	C20H15FN2S	334.41	109-101	92
BP20	C19H14FNS2	339.45	147-149	86

TABLE 2: ELEMENTAL ANALYSIS DATA OF 1,5-BENZOTHIAZEPINES (BP₁-BP₂₀)

Spectral Data for 1, 5-benzothiazepines (BP₁-BP₂₀) are given below:

BP-1:

2,3-Dihydro-2-(4-methylphenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₁): Mol.wt:, 347.45,yield: 89%,mp: 141-143⁰C ,IR (KBr) (cm^-1) : 1585 (C=N), 1505 (C=C), 1395 (C-N), 923 (C-F) and 654 (C-S).¹H-NMR (CDCl₃) ppm : 4.94 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.25 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.9 Hz, 1H, C₃-H-3a), 3.04 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 2.40 (3H, s, Ar-CH₃), 7.22 (1H, s, Ar-H), 7.61 (3H, m, Ar-H), 7.20-8.10 (8H, Ar-H).

BP-2:

2,3-Dihydro-2-(4-fluorophenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₂): Mol. wt: 351.41^, Yield: 89%, M.P: 152-154⁰C, IR (KBr) (cm^-1): 1625 (C=N), 1509 (C=C),1399 C-N), 689(C-S), 931 (C-F) ,  ¹H-NMR (CDCl₃) ppm : 5.27 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H),3.50 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.6 Hz, 1H, C₃-H-3a), 2.97 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.05 (1H, s,Ar-H), 7.19 (3H, m, Ar-H), 7.20-8.09 (8H, Ar-H).

BP-3:

2,3-Dihydro-2-(4-chlorophenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₃): Mol. wt: 367.87, Yield: 93%, M.P:144-145⁰C, IR (KBr) (cm^-1): 1595 (C=N ), 1502 (C=C), 1384 ( C-N), 778 (C-Cl), 921 (C-F) and  667 (C-S)  ¹H-NMR (CDCl₃) ppm : 5.0 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.53 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.9 Hz, 1H, C₃-H-3a), 3.39 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.25 (1H, s, Ar-H), 7.65 (3H, m, Ar-H), 7.22-8.08 (8H, Ar-H).

BP-4:

2,3-Dihydro-2-(2-chlorophenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₄): Mol. wt: 367.87, Yield: 71%, M.P:121-123⁰C, IR (KBr) (cm^-1): 1596 (C=N), 1510 (C=C), 1365 (C-N), 688 (C-S), 923 (C-F) and 805 (C-Cl)    ¹H-NMR (CDCl₃) ppm: 4.89 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.43 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.6 Hz, 1H, C₃-H-3a), 3.36 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.12 (1H, s, Ar-H), 7.72 (3H, m, Ar-H), 6.95-7.60 (8H, Ar-H).

BP-5:

2,3-Dihydro-2-(2,4-difluorophenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₅): Mol. wt: 369.40,yield:75%,mp:139-141⁰C.IR (KBr) (cm^-1) : 1612 ( C=N), 1501 ( C=C),1382 (C-N), 689 (C-S), 913 (C-F) and 944 (C-F)  ¹H-NMR (CDCl₃) ppm : 5.31 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.36 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.9 Hz, 1H, C₃-H-3a), 2.87 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.08 (1H, s, Ar-H), 7.30 (3H, m, Ar-H), 6.98-8.12 (7H, Ar-H).

BP-6:

2,3-Dihydro-2-(2,4-dichlorophenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₆): Mol. wt: 402.31,yield:86%,mp:118-120⁰C. IR (KBr) (cm^-1) : 1593 ( C=N), 1502 ( C=C), 1382 ( C-N), 687 (C-S), 925 (C-F) and 805 (C-Cl)   ¹H-NMR (CDCl₃) ppm : 5.10 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.27 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.6 Hz, 1H, C₃-H-3a), 2.66 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.15 (1H, s, Ar-H), 7.20 (3H, m, Ar-H), 7.05-7.95 (7H, Ar-H).

BP-7:

2,3-Dihydro-2-(2-chloro-5-nitrophenyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₇): Mol. wt: 412.86, Yield: 77%, M.p: 165-167⁰C,IR (KBr) (cm^-1) : 1588 (C=N), 1520 (N=O, asymmetric), 1505 ( C=C), 1382   ( C-N), 1340 (N=O, symmetric), 656 ( C-S), 933 (C-F) and 781 (C-Cl), ¹H-NMR (CDCl₃) ppm : 4.32 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.74 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.9 Hz, 1H, C₃-H-3a), 3.51 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.09 (1H, s, Ar-H), 7.12 (3H, m, Ar-H), 6.98-8.10 (7H, Ar-H).

BP-8:

2,3-Dihydro-2-(3-nitrophenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₈): Mol. wt: 378.42, Yield: 82%, M.p: 143-145⁰C,IR (KBr) (cm^-1) : 1580 (C=N), 1522 (N=O, asymmetric),1501 ( C=C), 1385   ( C-N), 1345 (N=O, symmetric), 924 (C-F) and 689 ( C-S), ¹H-NMR (CDCl₃) ppm : 5.42 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.38 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.6 Hz, 1H, C₃-H-3a), 2.86 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.30 (1H, s, Ar-H), 7.80 (3H, m, Ar-H), 7.48-8.60 (8H, Ar-H).

BP-9:

2,3-Dihydro-2-(4-nitrophenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₉): Mol. wt: 378.42, Yield: 89%, M.p: 129-131⁰C,IR (KBr) (cm^-1) : 1586 (C=N), 1515 (N=O, asymmetric), 1506 ( C=C), 1380   ( C-N), 1338 (N=O, symmetric), 925 (C-F) and 713 ( C-S), ¹H-NMR (CDCl₃) ppm : 5.42 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.47 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.7 Hz, 1H, C₃-H-3a), 3.10 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.18 (1H, s, Ar-H), 7.25 (3H, m, Ar-H), 7.25-8.20 (8H, Ar-H).

BP-10:

2,3-Dihydro-2-(3-hydroxyphenyl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₁₀): Mol.wt: 349.42, Yield: 84%, M.p: 227-229⁰C,IR (KBr) (cm^-1) : 1653 ( C=N), 1528  ( C-N), 1502 (C=C), 925 (C-F) and 694 (C-S), ¹H-NMR (CDCl₃) ppm : 3.85 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.34 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.0 Hz, 1H, C₃-H-3a), 2.41 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.25 (1H, s, Ar-H), 7.30 (3H, m, Ar-H), 7.15-7.80 (8H, Ar-H), 6.85 (1H, s, Ar-OH).

BP-11:

2,3-Dihydro-2-(3-nitro-4-methylphenyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₁): Mol. wt: 392.45, Yield: 94%, M.p: 177-1798⁰C,IR (KBr) (cm^-1) : 1642 ( C=N), 1548 (N=O, asymmetric), 1510 (C=C), 1380 (C-N), 1338  (N=O, symmetric), 927 (C-F) and 668 (C-S), ¹H-NMR (CDCl₃) ppm : 4.16 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.23 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.9 Hz, 1H, C₃-H-3a), 2.53 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 2.50 (3H, s, Ar-CH₃), 7.30 (1H, s,Ar-H), 6.70 (3H, m, Ar-H), 7.45-8.78 (7H, Ar-H)

BP-12:

2,3-Dihydro-2-(3,4,5-trimethoxyphenyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₂): Mol. wt:423.50, Yield:8 %, M.p: 149-151⁰C, IR (KBr) (cm^-1) : 1648 ( C=N), 1505 ( C=C), 1365 (C-N), 1225 (-O-CH₃), 923 (C-F) and 678 (C-S), ¹H-NMR (CDCl₃) ppm : 3.06 (dd, J_2,3a = 5.3 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 2.83 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.9 Hz, 1H, C₃-H-3a), 2.0 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.22 (1H, s,Ar-H), 6.60 (3H, m, Ar-H), 7.30-7.50 (6H, Ar-H), 3.70 (3H, s, Ar-OCH₃), 3.88 (6H, s, 2XAr-OCH₃)

BP-13:

2,3-Dihydro-2-(3,4-methelenedioxyphenyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₃): Mol.wt:377.47, Yield: 74%, M.p: 155-157⁰C,IR (KBr) (cm^-1) : 1592 (C=N), 1502 ( C=C), 1370 (C-N),1232 (-O-CH₂-O-), 921 (C-F) and 689 (C-S), ¹H-NMR (CDCl₃) ppm : 4.94 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.25 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.1 Hz, 1H, C₃-H-3a), 3.14 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.25 (1H, s,Ar-H), 7.40 (3H, m, Ar-H), 6.10 (2H, s, O-CH₂-O), 7.21-7.85 (7H, Ar-H)

BP-14:

2,3-Dihydro-2-(5-bromofuran-2-yl)-4-(4-fluoro phenyl)-1,5-benzothiazepine (BP₁₄): Mol. wt: 402.28, Yield: 79%, M.p: 133-135⁰C, IR (KBr) (cm^-1): 1602 (C=N), 1505 (C=C), 1340 (C-N), 664 (C-S), 933 (C-F) and 790 (C-Br) , ¹H-NMR (CDCl₃) ppm : 5.07 (dd, J_2,3a = 5.3 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 4.10 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.2 Hz, 1H, C₃-H-3a), 3.39 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.10 (1H, s,Ar-H), 6.80 (3H, m, Ar-H),  6.80-7.30 (6H, Ar-H)

BP-15:

2,3-Dihydro-2-(4-dimethylaminophenyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₅): Mol. wt: 376.49, Yield: 88%, M.p: 115-117⁰C, IR (KBr) (cm^-1): 1608 (C=N), 1509 (C=C), 1390 (C-N), 1175 (-N-(CH₃)₂), 933 (C-F) and 679 (C-S),NMR (CDCl₃) ppm : 4.96 (dd, J_2,3a = 5.3 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.83 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.2 Hz, 1H, C₃-H-3a), 3.26 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 3.20 (6H, s, N-(CH₃)₂, 7.20 (1H, s,Ar-H), 7.45 (3H, m, Ar-H), 6.70-8.20 (8H, Ar-H)

BP-16:2,3-Dihydro-2-(3-methoxy-4-hydroxy phenyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₆): Mol.wt:379.45, Yield: 86%, M.p: 152-154⁰C, , IR (KBr) (cm^-1): 3540 (O-H), 1598 (C=N), 1502 (C=C), 1378 (C-N), 1234 (-O-CH₃) 913 (C-F), and 688 (C-S) NMR (CDCl₃) ppm : 3.43 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 2.50 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.4 Hz, 1H, C₃-H-3a), 1.03 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.20 (1H, s,Ar-H), 6.85 (3H, m, Ar-H), 7.15-7.90 (7H, Ar-H), 6.95 (1H, s, Ar-OH), 3.80 (3H, s, Ar-O-CH₃)

BP-17:

2,3-Dihydro-2-(2-pyridinyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₇): Mol.wt:334.41, Yield: 78%, M.p: 112-114⁰C,1602 (C=N), 1510 (C=C), 1390 (C-N), 924 (C-F) and 677 (C-S) ,NMR (CDCl₃) ppm : 4.91 (dd, J_2,3a = 5.3 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.44 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.4 Hz, 1H, C₃-H-3a), 1.05 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.15 (1H, s,Ar-H), 7.20 (3H, m, Ar-H), 7.10-8.15 (8H, Ar-H)

BP-18:

2,3-Dihydro-2-(3-pyridinyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₈): Mol.wt:334.41, Yield: 82%, M.p: 119-121⁰C, IR (KBr) (cm^-1):1599 (C=N), 1506 (C=C), 1382 (C-N), 927 (C-F) and 698 (C-S), NMR (CDCl₃) ppm : 4.38 (dd, J_2,3a = 5.3 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.37 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.8 Hz, 1H, C₃-H-3a), 1.07 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.25 (1H, s,Ar-H), 7.30 (3H, m, Ar-H), 6.75-8.90 (8H, Ar-H)

BP-19:

2,3-Dihydro-2-(4-pyridinyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₁₉): Mol.wt:334.41, Yield: 92%, M.p: 109-111⁰C, IR (KBr) (cm^-1):1606 (C=N), 1508 (C=C), 1388 (C-N), 933 (C-F) and 654 (C-S), NMR (CDCl₃) ppm : 4.67 (dd, J_2,3a = 5.1 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.42 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.8 Hz, 1H, C₃-H-3a), 2.50 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.20 (1H, s,Ar-H), 7.50 (3H, m, Ar-H), 6.95-8.68 (8H, Ar-H)

BP-20:

2,3-Dihydro-2-(2-thienyl)-4-(4-fluorophenyl)-1,5-benzothiazepine (BP₂₀): Mol.wt:339.45, Yield: 86%, M.p: 147-149⁰C, IR (KBr) (cm^-1):1605 (C=N), 1503 (C=C), 1386 (C-N), 928 (C-F) and  644 (C-S), NMR (CDCl₃) ppm : 5.50 (dd, J_2,3a = 5.3 Hz, J_2,3b = 12 Hz, 1H, C₂-H), 3.53 (dd, J_3a,3b = 14.4 Hz, J_3a,2 = 9.9 Hz, 1H, C₃-H-3a), 2.90 (t, J_3b,3a = J_3b,2 = 12.9 Hz, 1H, C₃-H-3b), 7.20 (1H, s,Ar-H), 7.34 (3H, m, Ar-H), 6.60-7.80 (7H, Ar-H)

Antibacterial activity: The antibacterial activity was tested by determining the minimum inhibitory concentration (MIC) for each compound using Standard Serial Tube Dilution Technique. The organisms used are

Gram positive bacteria: Staphylococcus aureus (NCIM-2079), Bacillus subtilis (NCIM-2063)

 Gram negative bacteria:  Escherichia coli (NCIM-2068), Proteus vulgaris (NCIM-2027)

Antifungal activity: The antifungal activity was tested by the same procedure as described in the antibacterial activity, except using Potato-Dextrose-Agar medium.

The organisms used are: Aspergillus niger (ATCC-6275), Candida tropicalis (ATCC-1369)

The results are presented in Table 3.

TABLE 3: ANTIBACTERIAL ACTIVITY OF 1, 5-BENZOTHIAZEPINES (BP₁ TO BP₁₂): (Expressed as MIC in µg/mL)

DISCUSSION ON RESULTS:

Antibacterial activity: From the above results, it is evident that most of the 1,5-benzothiazepines synthesized showed antibacterial activity with different MIC values against the tested organisms, but not comparable with that of the standard. Among the compounds tested against B. subtilis, the compounds, BP₃ having a chlorophenyl moiety, BP₅ having a difluorophenyl moiety, BP₆ having a dichlorophenyl moiety, BP₁₀ having a hydroxyl-lphenyl and BP₁₅ having a dimethylaminophenyl moiety proved to be more potent with a MIC value of 64 µg/mL in each case. Against S.aureus, BP₄, BP₅, BP₇ (2-chloro-5-nitrophenyl moiety), BP₁₄ (bromofuran moiety), BP₁₅ and BP₁₉    (4-pyridinyl moiety) showed maximum activity with a MIC value of 64 µg/mL in each case. Against E. coli BP₅ proved to be the most potent with a MIC value of 32 µg/mL. This is followed by compounds, BP₆, BP₉ (nitrophenyl moiety), BP₁₂ (trimethoxyphenyl moiety), BP₁₄ and BP₁₉ with a MIC value of 64 µg/mL in each case. Against P. vulgaris, BP₅, BP₁₀, BP₁₅ and BP₂₀ (thienyl moiety) showed maximum activity with a MIC value of 64 µg/mL in each case.

Procedure for Antifungal activity: The antifungal activity was tested by the same procedure as described in the antibacterial activity, except using Potato-Dextrose-Agar medium. The results are presented in Table 4.

TABLE 4: ANTIFUNGAL ACTIVITY OF 1,5-BENZOTHIAZEPINES (BP₁ TO BP₁₂)

Antifungal activity: From the above results, It is noticed that the 1, 5-benzothiazepines tested showed more antifungal activity than the antibacterial activity. Among the compounds tested against A. niger, the compounds, BP₅ having a difluorophenyl moiety, BP₆ having a dichlorophenyl moiety, BP₇ having a 2-chloro-5-nitrophenyl moiety, BP₁₄ having a bromofuran moiety and BP₁₉ having a 4-pyridinyl moiety proved to be the most potent compounds with a MIC value of 16 µg/mL in each case. This was followed by the compounds, BP₂ (fluorophenyl moiety), BP₃ and BP₄ (chlorophenyl moieties), BP₈ and BP₉ (nitrophenyl moieties), BP₁₇ (2-pyridinyl moiety) and BP₂₀ (thienyl moiety) with a MIC value of 32 µg/mL in each case. Against C. tropicalis, the compounds, BP₅ and BP₂₀, showed maximum activity with a MIC value of 16 µg/mL in each case.

This was followed by compounds, BP₁ (methylphenyl), BP₆, BP₇ (2-chloro-5-nitrophenyl moiety), BP₁₄ and BP₁₉ with a MIC value of 32 µg/mL in each case.

 Cytotoxicity Studies: The in vitro cytotoxicity of the test compounds was evaluated by the MTT assay. HT-29 (colon cancer), MCF-7 (breast cancer) and DU-145 (prostate cancer) cell lines were obtained from ACTREC, Mumbai, India.

Cytotoxicity evaluation: The cells were seeded in 96 well plates at a density of 1x10⁴ (counted by Trypan blue exclusion dye method)per well and were incubated for 24 h to recover. After incubation the medium was replaced with fresh media containing different dilutions of the test compounds. Then the plated were incubated for additional 48 h at 37⁰C in DMEM/MEM with 10% FBS medium. Following incubation, the medium was removed and replaced with 90 μl of fresh DMEM without FBS. To the above wells, 10 μl of MTT reagent (5 mg/mL of stock solution in DMEM without FBS) was added and incubated at 37^oC for 3-4 h, there after the above media was replaced by adding 200 μl of DMSO to each well and incubated at 37⁰C for 10 min. The absorbance at 570 nm was measured on a spectrophotometer. Methotrexate was used as reference drug for comparison. The results are presented in Table 5.

TABLE 5: CYTOTOXICITY OF THE NEW 1,5-BENZOTHIAZEPINES (BP₁ TO BP₁₁): (IC₅₀ values in μg/mL)

Data presented as mean ± SD (n=3). All the compounds and the standard dissolved in DMSO, diluted with culture medium containing 0.1% DMSO. The control cells were treated with culture medium containing 0.1% DMSO.  NA- No Activity (i.e IC50 > 200 μg/mL)

DISCUSSION ON RESULTS:

Cytotoxic studies: Of all the compounds tested against HT-29 cell lines, the compound BP₅ having a difluorophenyl moiety in its structure showed maximum activity with a IC₅₀ value of 28 µg/mL. This is followed by compounds, BP₂₀ having a thienyl moiety (IC₅₀ 36 µg/mL), BP₂ and BP₆ having fluorophenyl and dichlorophenyl moieties respectively (IC₅₀ 42 µg/mL), BP₁ having a methylphenyl moiety (IC₅₀ 55 µg/mL) and BP₁₄ having a bromofuran moiety (IC₅₀ 56 µg/mL). The other compounds also showed activity but at a higher IC₅₀ values.

Among the compounds tested for cytotoxicity on MCF-7 cell lines, the compound BP₁₄ showed maximum activity (IC₅₀ 27 µg/mL). This was followed by compounds, BP₂₀ (IC₅₀ 28 µg/mL), BP₅ (IC₅₀ 42 µg/mL) and BP₂ (IC₅₀ 48 µg/mL). All the other compounds showed cytotoxicity at higher values.

Among the compounds tested for cytotoxicity on DU-145 cell lines, the compounds, BP₁₄ and BP₂₀ showed maximum activity (IC₅₀ 16 µg/mL). This was followed by compounds, BP₅ (IC₅₀ 33 µg/mL), BP₁₁ having a 3-nitro-4-methylphenyl moiety (IC₅₀ 46 µg/mL), BP₁ (IC₅₀ 52 µg/mL) and BP₆ (IC₅₀ 56 µg/mL).

It was also observed that among all the compounds tested on these three cell lines, most of the compounds showed maximum activity on prostate cancer cell lines (DU-145).

ACKNOWLEDGMENTS: One of the authors (Venkata rao vutla) is thankful to the ACTREC Research center Mumbai for providing cytotoxic evaluation studies and to the Principal, Andhra University College of Pharmaceutical Sciences, Visakhapatnam for providing required help in carrying out the pharmacological studies

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How to cite this article:

Vutla VR, Yejella RP and Nadendla R: Synthesis of novel 1, 5-dihydrobenzothiazepine derivatives by conventional and microwave irradiation methods and their pharmacological activities. Int J Pharm Sci Res 2014; 5(2): 453-62.doi: 10.13040/IJPSR. 0975-8232.5(2).453-62

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