SYNTHESIS OF SOME N-HETROCYCLIC ANALOGS OF VASICINE

SYNTHESIS OF SOME N-HETROCYCLIC ANALOGS OF VASICINE

1. MAHAJAN^*1, K. L. DHAR², O. P SURI.², K. NEPALI², N. KAMRA.³, A. GARG⁴, A. SHARMA ⁵

Department of Pharmaceutical Sciences, Lovely School of Pharmaceutical Sciences, Lovely Professional University*¹, Phagwara, Punjab., India

Department of Pharmaceutical Chemistry, ISF college of Pharmacy², Moga, 142001, Punjab., India

Department of Pharmaceutical Chemistry, B. N. College of Pharmacy³, Udaipur, Rajasthan

Bharti Institute of Pharmaceutical Sciences⁴, Sri Ganganagar, Rajasthan, India

Department of Chemistry, Lovely School of Chemistry, Lovely Professional University⁵, Phagwara, Punjab., India

ABSTRACT

Vasicine is a pyrralazoquinazoline monobasic alkaloid obtained from the Plant Adhatoda vasica. In the present paper, the experiment were carried out to synthesis the various analogs of Vasicine, where the five membered ring C, was converted to seven membered ring, thus producing 7,8,9,10-Tetrahydroazepino[2,1-b] quinazolin-12(6H)one (RLX), was reported to be 6-10 times more potent than aminophylline as a bronchodilatory agent. A series of new compounds were synthesized, as modification in ring A and in ring B. The resulted compounds were evaluated for the antihistaminic activity to synthesis even more potent compounds.

Keywords:

Vasicine,

RLX,

Antihistamanics

INTRODUCTION:

Adhatoda vasica Nees. (Acantheace) leaves have been used in Indian system of medicines for many centuries.¹ Adhatoda vasica contains two major alkaloids, vasicine and vasicinone.^{2, 3} Vasicine is reported to have antihistaminic effects, uterine stimulant activity, moderate hypotensive activity⁴, thrombopoeitic activity⁵, it relieves from cough and breathlessness⁶, its local use gives relief in pyorrhoea and in bleeding gums ⁷. Autooxidised product of vasicine, vasicinone was also reported to cause bronchodilatory effect both in vivo and in vitro, but it was later proved in IIIM Jammu that vasicinone is of little activity.

First, it was reported that configuration at C-3 is R but now it has been established that C-3 has S configuration. Therefore, a number of compounds were synthesized to find a relation between the structure and bronchodilatory activity. In first instances, ring A substituted vasicine were synthesized which on pharmacological screening revealed no enhancement of activity. Next attention was concentrated on ring B and deoxyvasicine was prepared which have little or no bronchodilatory activity.

It was interesting to note that with increase in size of ring C activity got enhanced and deoxydihomo “C” vasicinone was found to be 6 -10 times more potent than aminophylline.

The seven membered ring C analogue 7, 8, 9, 10-Tetrahydroazepino [2, 1-b] quinazolin-12-(6H)-one, has been synthesized in IIIM Jammu. It showed marked increase in bronchodilatory activity.

7, 8, 9, 10- Tetrahydroazepino[2, 1- b] quinazolin-12-(6H)-one

A series of analogues of vasicine were prepared for the bronchodilatory activity. For example Vasicine like compound – Bromhexine:

Bromhexine (2- amino- 3, 5- dibromo- N- cyclohexyl- N-methylbenzenemethanamine)

It was concluded that only one of two oxygen function is required i.e. either at C-9 or C-3. So deoxyvasicinone is active and vasicinone has little or no bronchodilatory activity as compared to vasicine.

With increase in size of ring C upto 7 carbons bronchodilatory activity  get enhanced but thereafter increase in ring size decreases the activity. Structure activity relationship studies lead to synthesis of 7, 8, 9, 10-Tetrahydroazepino [2, 1-b] quinazolin-12(6H) one which was found to be potent bronchodilator.

Pharmacological studies have shown that it does not have any untoward effect.

The objective of the present studies was to carry out the various substitutions at ring A & B to synthesis even more potent bronchodilator with less untoward effects.

PROPOSED SCHEME:

PART –A

REDUCTION OF C=N

PART –B

N-ALKYL/ALKANOYL/BENZYL SUBSTITUTION

Modification of Ring A

Modification of Ring B

EXPERIMENTAL:

Melting points were determined on Buchi 535 M.pt. apparatus. Mass spectra were recorded on JEOL JMS D-300 mass spectrometer at 70 eV and IR spectra on Hitachi 270-30 spectrophotometer. NMR spectra were recorded on Bruker DPX-200 spectrometer. Elemental analytical data have been determined on Carlo Erba, Model 1106, and elemental analyzer. Microwave irradiation was carried out in BPL BMC 900T commercial microwave oven operating at a frequency of 2450 MHz.

SPECTRAL DATA OF PRODUCTS:

RLX:  7, 8, 9, 10-Tetrahydroazepino [2, 1-b] quinazolin-12 (6H) one

¹H NMR (200 MHz, CDCl₃,) δ 08.25 (1H, d, J= 8.12 Hz, H- 1), 7.10-7.90 (3H, m, H-2, 3, 4), 4.20 (2H, t, H-10), 3.15 (2H, t, H-6), 1.7- 2.20 (6H, bs, H-7, 8, 9).

¹³C NMR (50 MHz, CDCl₃) δ  136.3 (C-1), 127.8 (C-1a), 120.5 (C-2), 129 (C-3), 118(C-4), 137(C-4a), 158.3 (C-5a), 32.8 (C-6), 24.1(C-7),26.4(C-8),28.9(C-9),44.468(C-10),164(C-12).

RLX-H: 5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one

¹H NMR (200 MHz, CDCl3, δ, TMS=0) 7.88 (1H, d, J= 7.79Hz, H-1) 7.26 (1H, dd, J=1.39 and

7.79Hz, H-3), 6.82 (1H, dd, J=1.35 and 7.79Hz, H-2), 6.64 (1H, d, J=7.79Hz, H-4), 4.94 (1H, t H-5a), 4.46 (2H, t H-10), 2.93 (2H, m, H-6), 1.25-2.14 (6H, m, H-7, 8, 9).

¹³C NMR (50 MHz, CDCl3) δ 135.47 (C-1), 117.82 (C-2), 130.38 (C-3), 116.531 (C-4), 149.31 (C-4a), 72.27 (C-5a), 36.87 (C-6), 25.49 (C-7), 29.89 (C-8), 31.05 (C-9), 44.830 (C-10), 166.36 (C-12), 120.80 (C-1a).

CA-1: 2-Bromo-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b]- quinazoline -12 (5H) one

¹H NMR (200MHz, CD3OD, δ, TMS=0) 8.4 (1H, d, J=2.20 Hz, H-1), 8.07 (2H, dd, J=2.25 and 7.85 Hz,H-3), 7.6 (1H, d, J=8.64 Hz,H-4), 4.20 (2H, t, H-10), 3.15 (2H, m, H-6), 1.7-2.20 (6H, bs, H-7, 8, 9).

CA-2: 2, 4-Dibromo-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one

¹H NMR (200MHz, CDCl3, δ, TMS=0) 8.35 (1H, d, J=2.21 Hz, H-1), 8.09 (2H, d, J=2.21 Hz, H-3), 4.30 (2H, t, H-10), 3.01 (2H, t, H-6), 1.7-2.20 (6H, bs, H-7, 8, 9).

CA-3: 2, 4-Dimethoxy-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one

¹H NMR (200MHz, CDCl3, δ, TMS=0) 7.9 (1H, d, J=2.04, H-1), 7.03 (1H, d, J=2.04, H-3), 4.0 (6H, s, OCH3 -2,4) 4.30 (2H, t, H-10), 3.01 (2H, t, H-6), 1.7-2.20 (6H, bs, H-7, 8, 9).

CA-4: -2, 4-Dihydroxy-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one

¹H NMR (200MHz, CD3OD, δ, TMS=0) 7.6 (1H, d, J=2.04, H-1), 7.02 (1H, d, J=2.04, H-3), 4.0 (4H, s, OH-2, 4), 4.30 (2H, t, J=3.56 and 4.19 Hz, H-10), 3.01 (2H, t, H-6), 1.7-2.20 (6H, bs, H-7, 8 ,9).

CA-5: 2-Nitro-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one

¹H NMR (200MHz, CDCl3, δ, TMS=0) 9.01 (1H, d, J=2.58Hz,H-1), 8.45 (2H, dd, J=2.58 and 7.83Hz, H-3), 7.7 (1H, d, J=8.97Hz, H-4), 4.20 (2H, t, H-10), 3.15 (2H, t, H-6) ,1.7-2.20 (6H, bs, H-7, 8, 9).

CA-6: -5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one -2- sulfonic acid

¹H NMR (200MHz, CDCl3, δ, TMS=0) 8.9 (1H, d, J=2.58Hz, H-1), 8.35 (2H, dd, J=2.58 and 7.83Hz, H-3), 7.6 (1H, d, J=8.97, H-4), 4.20 (2H, t, H-10), 3.15 (2H, t, H-6), 1.7-2.20 (6H, bs, H-7, 8, 9).

CB-1: 5-Methyl-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12(5H) one

¹H NMR (200 MHz, CDCl3) δ 7.98 (1H, d, J= 7.83Hz, H-1), 7.36 (1H, dd, J= 1.49 and 7.83 Hz, H-3), 6.92 (1H, dd, J= 1.35 and 7.85, H-2), 6.63 (1H, d, J= 7.79 Hz, H-4), 4.98 (1H, t, H-5a), 4.46 (2H, t, H-10), 2.94 (3H, s, H-5), 1.25-2.14 (8H, m, H-6, 7, 8, 9).

CB-2: 5- Ethyl-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12(5H) one

¹H NMR (200 MHz, CDCl3) δ 7.81 (1H, dd, J=7.86 Hz, H-1), 7.34 (1H, dd, J=1.41 and 7.83Hz, H-3), 6.78 (1H, dd, J=1.41 and 7.73 Hz, H-2), 6.63 (1H, d, J=7.79, H-4), 3.40 (2H, q, H-1΄), 4.98 (1H, t, H-5a), 4.46 (2H, t, H-10), 1.25-2.14 (11H, m, H-6, 7, 8, 9, 2΄).

CB-3: 5-Propyl-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline-12 (5H) one

¹H NMR (200MHz, CDCl3, δ, TMS=0) δ 7.78 (1H,d, J= 7.83 Hz, H-1), 7.32 (1H, dd, J=1.42 and 7.87 Hz, H-3), 6.78 (1H, dd, J=1.35 and 7.86 Hz, H-2), 6.61 (1H, d, J=7.79 Hz, H-4) 3.35 (2H, t, J=3.66 and 4.21 Hz, H-1΄), 4.85 (1H, t H-5a), 4.46 (2H, t, J=4.58 Hz, H-10), 1.25-2.14 (13H, m, H-6, 7, 8, 9, 2΄, 3΄).

CB-4: 5-Acetyl-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one

¹H NMR (200 MHz, CDCl3) δ 8.06 (1H, d, J= 7.86 Hz ,H-1), 7.26-7.63 (1H, m, H-2,3,4), 2.95( H, m,J =6.31 Hz, H-5a, 10b), 4.45 (2H, t, H-10a), 2.21 (3H, s, H-5) 1.25-2.04 (8H, m, H-6, 7, 8, 9).

CB-5: 5-Benzyl-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12(5H) one

¹H NMR (CDCl3, 200MHz,) δ 7.98 (1H, d, J=7.61Hz, H-1), 7.26-7.34

(6H, m, H-3, 2΄, 3΄, 4΄, 5΄, 6΄), 6.71 (1H, t, H-2), 6.66 (H-4, d, J=7.60 Hz, H-4), 5.59 (1H, t, H-5a), 1.25-2.14 (8H, m, H-6, 7, 8, 9), 3.01 (1H, m, H-10a), 4.56 (1H, m, H-10b).

CB-6: 5-Benzoyl-5a, 6, 7, 8, 9, 10-Hexahydroazepino [2, 1-b] - quinazoline -12 (5H) one

¹H NMR (CDCl3, 200MHz) δ 7.98 (1H, d, J=7.61 Hz, H-1), 7.26-7.34 (6H, m, H-3, 2΄, 3΄, 4΄, 5΄, 6΄), 6.71 (1H, t, H-2), 6.66 (H-4, d, J=7.60 Hz, H-4), 5.59 (1H, t, H-5a), 1.25-2.14 (8H, m, H-6, 7, 8, 9), 3.01 (1H, m, H-10a), 4.56(1H, m, H-10b).

PHARMACOLOGICAL ACTIVITY:

MATERIAL & METHODS:

Animals - Guinea pig of either sex 300-500g; Drugs- Etofylline, Test compounds; Physiological solution: Krebs-Heneseleit solution (KHS). The prepared compounds were tested for in vivo Bronchodilator activity. The isolated guinea pig tracheal chain preparation was used following the method described by Castillo and de beer³³ except the tracheal ring were opened by severing the cartilage³⁴. Inhibition of histamine and acetylcholine induced isotonic contraction in isolated guinea pig tracheal chain preparations were observed. Etofylline was used as standard bronchodilator.

Guinea pigs of either sex, weighing 300-500g, were sacrificed by head below and carotid bleeding. The trachea was dissected out and transferred to a dish containing Krebs-Heneseleit solution (KHS) and cut transversely between the segments of cartilage, so as to give number of rings of trachea. About 7-8 of these were tied to form the chain of approximately 4-5 cm in length. The chain was suspended in 20ml of organ bath containing KHS continuously aerated with 95% oxygen and 5% carbon dioxide and maintained at 37 ºC. The composition (m moles) of KHS was NaCl 118, KCl 4.7,  MgSO₄.7H₂O 1.2, CaCl₂ 2.2  KH₂PO₄ 1.2, NaHCO₃ 24.9 and (+) – glucose 11.1 .The response was recorded isotonically on a kymograph. The tissue was adjusted to an initial tension of 1.5g and allowed to equilibrate (60-90min)  The relaxation effect of the compounds was studied on the tracheal chain precontrected with histamine diphosphate (110-6 g/ml).  The test compounds were tested as percent of relaxing of pre-contracted muscle back to baseline tension ( 100%) if there was relaxation to slightly below the base line it was also taken as 100% relaxation¹⁰.

RESULTS AND DISCUSSIONS:

7, 8, 9, 10-Tetrahydroazepino [2, 1-b] quinazolin-12-(6H)-one (RLX) was synthesized and various substitutions were made on the Rings A and B. The compounds were purified by repeated crystallization from appropriate solvent. The structures of the compounds were ascertained by spectral data.

The synthesised compounds were evaluated for their in vitro bronchodilatory activity using isolated guinea pig tracheal chain. The results are summarized in table 3 and a comparative study has been illustrated with the help of fig. 1. The RLX showed 65% relaxation activity against histamine- induced tracheal contraction as compared to 43% relaxation shown by etofylline. The substitution of one H-atom to N-5 in ring B of RLX leads to RLX-H, which completely blocked the relaxation effect of RLX. Further, the substitution of bromine at R₂ in ring A (CA-1) & methyl substitution at N-5 of ring B (CB-2) showed only slight relaxation activity with 31% & 32% respectively. However, none of the modified compounds showed significant bronchodilatory effect on isolated guinea pig tracheal chain as compared to etofylline, as shown in fig. 1.

Table1:  List of products synthesised after modification of Ring A

Table 2:  List of products synthesised after modification of Ring B 

The synthesized compounds were evaluated for the bronchodilatory activity. 

Table 3: Bronchodilator Activity Evaluation of Vasicine Analogues

Figure 1: Comparative Bronchodilatory Activity of Test Compounds with Etofylline

CONCLUSION:

It may be concluded that the loss of activity in CA-1 to CA-6 & CB-1 to 6, as well as in the parent compound, may be due to antagonistic effect of the stereoisomers.

ACKNOWLEDGEMENT:

The authors are grateful to S. Kaul, Scientist at IIIM, Jammu for his guidance & support in this research. We are also thankful to Dr. Rao, University Institute of pharmaceutical Sciences, Panjab University, Chandigarh for his support in this project.

REFERENCES:

1. Pandita K: Seasonal variation of alkaloids of Adhatoda vasica and detection of glycosides and N-Oxides of vasicine and vasicinone. Planta Med. 1983; 48: 81-82.
2. Atal CK: Chemistry and Pharmacology of vasicine - A new oxytocic and abortifacient. P.58, New Delhi 1980.
3. Chopra RN: Some observations on the pharmacological action and therapeutic properties of Adhatoda vasica. J. Med. Res. 1925; 13: 205.
4. Amin, AH and Mehta DR: A bronchodilator alkaloid (vasicinone) from Adhatoda vasica Nature 1959; 184:1317.
5. Atal CK et al.: Thrombopoeitic activity of vasicine hydrochloride. Ind. J. Exp. Biol. 1982; 20:704-709.
6. Gogate VM: Dravyagunavignyana, Continental Prakashan, Pune. Ind. J. Physiol. Pharmacol. 1982; 32(2): 120-125.
7. Doshi JJ al: Effect of Adhatoda vasica Massage in Pyorrhoea. Pharmaceutical Biology 1983; 21(4):173-176.
8. Castillo JC and de Beer ED: The tracheal chain. I.A preparation for the study of antispasmodics with particular reference to bronchodilator drugs. J. Pharmacol. Exp. Ther. 1974; 90: 104-112.
9. Akcasu A: The physiologic and pharmacologic characteristics of the tracheal muscle. Arch. Int. Pharmacodyn.Ther. 1959; 122: 201-207.

10. Mahindroo N et al: Synthesis and Structure-Activity Relationships of Vasicine Analogues as Bronchodilatory Agents. Medicinal Chemistry Research 2005; 14(6): 347-368.
11. Dhar KL et al: Studies on Some Biologically Active Azepinoquinazolines: Part I- An Approach to Potent Bronchodilatory Compounds. Indian J. Chem. 1988; 27B, 937-940.
    

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