INTRODUCTION:

An interesting feature of Schiff bases¹ is that they serve on reduction afforded reduced products due to the presence of –CH=N moiety. The reduction of Schiff bases with Lithium Aluminum Hydride has not been very comfortable often the yields are accompanied by carry material.

A variety of secondary amines were found to posses antibacterial, fungicidal and anti-inflammatory activities² In connection with di-secondary amines, it was found desirable to prepare secondary amines from their corresponding Schiff bases, some of which contained groups which are usually reducible. The need for nitrosubstituted secondary amines eliminated the possible use of catalytic hydrogenation of the corresponding Schiff bases. All other methods of reduction thus, for reported in the literature were eliminated as possibilities on the basis of this need. Since sodium borohydride^3-6 is such a highly selective reducing agent and normally will not attack the nitro group, carboxylic group, attention was focused on its potential use for the reduction of Schiff bases^7-8. These synthesized secondary amines were screened for their antibacterial activity against Xanthomones citri, Escherichia coli, Erwinia carotovara and Bacillus subtilis:

Penicillin was used as standard antibiotic for comparison. Further the structures of synthesized compounds were confirmed by elemental analysis and spectral data (IR, ¹HNMR)

Scheme: 1

Comp. (Ia-m)

Where,

Entry	R	R¹	R²	R³	R⁴
Ia	H	H	NO₂	H	I
Ib	H	H	I	H	NO₂
Ic	H	H	I	H	Cl
Id	H	H	Cl	H	I
Ie	I	H	CH₃	H	I
If	I	H	NO₂	H	I
Ig	CH₃	I	H	NO₂	H
Ih	H	H	COOH	H	I
Ii	I	H	COOH	H	I
Ij	I	H	H	NO₂	H
Ik	H	H	H	Cl	I
Il	H	H	I	H	COOH
Im	Cl	H	I	H	Cl

Table 1 Physical and analytical data of secondary amines I (a-m)

Entry	Mol. Formula	Mol. Weight	M.P. (^oC)	Yield (%)	Halogen analysis X (Cl, Br, I) % Found (Calculated.)
Ia	C₁₉H₁₄N₂O₃I₂	572	150	80	44.40 (44.54)
Ib	C₁₉H₁₄N₂O₃I₂	572	120	87	44.40 (44.32)
Ic	C₁₉H₁₄NOI₂Cl	561.5	135	72	51.47 (51.31)
Id	C₁₉H₁₄NOI₂Cl	561.5	138	85	51.47 (51.53)
Ie	C₂₀H₁₆NOI₃	667	140	87	57.12 (57.23)
If	C₁₉H₁₃N₂O₃I₃	698	158	88	54.58 (54.42)
Ig	C₂₀H₁₆N₂O₃I₂	586	115	80	43.34 (43.39)
Ih	C₂₀H₁₅NO₃I₂	571	140	85	44.48 (44.40)
Ii	C₂₀H₁₄NO₃I₃	697	118	80	54.66 (54.31)
Ij	C₁₉H₁₄N₂O₃I₂	572	122	87	44.40 (44.32)
Ik	C₁₉H₁₄NOI₂Cl	561.5	142	85	51.47 (50.01)
Il	C₂₀H₁₅NO₃I₂	571	148	82	44.48 (44.28)
Im	C₁₉H₁₃NOI₂Cl₂	596	160	90	54.52 (54.41)

EXPERIMENTAL:

All melting points are taken in open glass capillaries and were found uncorrected. The purity of compounds has been checked by T.L. C. on silica gel G. The IR spectra in KBr were recorded on shimazu spectrophotometer and ¹HNMR spectra were recorded in DMSO on varian Inova 300 FT MHz spectrophotometer using TMS as a internal standard (d, ppm).

Synthesis of secondary amines (Ia-m):

A Schiff base (0.01 mole) was dissolved in methanol and sodium borohydride (0.37 gm, 0.01 mole) was added in small installments within 10 min. The reaction mixture was allowed to stand for 1 hr. The excess of solvent was removed by evaporation. The residue was washed with cold water and crystallized from ethanol to give compounds (Ia-m) (Table-1) (Scheme-1)

Reduction of N(2-iodo-4-nitrophenyl)-3-iodo-4-hydroxy biphenyl-5yl azomethine (Ia):

IR (KBr) cm^-1: 1510, 1450 (NO₂), 3350 (OH) 3420, 3400 (NH), 1566, 1494, 1406 (C=C) ¹HNMR (300 MHz, DMSO): d 4.95 (s, 2H, CH₂), 6.2 (s, 1H, NH), 11.2 (s, 1H, Ar-OH), 7.2-8.3 (m, 10H, Ar-H).

Reduction of N (2, 6-di-iodo-4-methyl phenyl)-3-iodo-4-hydroxy biphenyl-5yl azomethine (Ie):

IR (KBr) cm^-1: 3325 (NH), 2960, 2890 (CH₃), 3348 (OH) 1590, 1500, 1445 (C=C) ¹HNMR (300 MHz, DMSO): d 2.6 (s, 3H, CH3), 3.92 (s, 2H, CH₂), 6.5 (s, 1H, NH), 11.28 (s, 1H, Ar-OH), 7.1-8.7 (m, 9H, Ar-H).

Reduction of N (3-ido-2-methyl-4-nitro Phenyl)-3-iodo-4-hydroxy biphenyl-5yl azomethine (Ig):

IR (KBr) cm^-1: 1540, 1360 (NO₂), 2950, 2895 (CH₃) 3358 (OH) 3370 (NH), 1566, 1485, 1410 (C=C) ¹HNMR (300 MHz, DMSO): d 2.5 (s, 3H,CH₃) 4.6 (s,2H, CH₂), 5.9 (s,1H,NH), 10.95 (s, 1H, Ar-OH), 7.0-7.8 (m, 9H,Ar-H).

Reduction of N (2,6-dichloro-4-iodo phenyl)-3-iodo-4-hydroxy biphenyl-5yl azomethine (Im):

IR (KBr) cm^-1: 3340 (NH), 3350 (OH), 1625, 1590, 1445 (C=C) ¹HNMR (300 MHz, DMSO): d 4.2(s, 2H, CH₂), 6.1 (s, 1H, NH), 11.10 (s, 1H, Ar-OH), 7.1-8.9 (m, 9H, Ar-H).

Table-2 Antibacterial activity of compounds (Ia-m)

Entry	Zone of inhibition (mm)
Entry	*Xc.*	*E.Coli*	*Ec.*	*Bs.*
Ia	07.20	06.00	07.00	03.00
Ib	05.00	06.00	05.00	04.00
Ic	10.02	12.01	12.00	00.00
Id	15.00	16.00	16.02	02.00
Ie	18.00	18.50	18.20	06.00
If	08.00	07.80	08.20	00.02
Ig	11.00	11.20	10.80	00.08
Ih	16.00	16.20	16.00	00.05
Ii	20.00	19.10	20.01	00.00
Ij	05.50	06.00	06.10	00.00
Ik	12.00	12.50	12.00	01.00
Il	14.00	15.02	14.80	01.02
Im	22.00	22.02	18.08	04.00
Penicillin (200ppm)	21.00	22.00	19.00	23.00

In vitro-antibacterial Activity:

The newly synthesized compounds were subjected to antibacterial screening by using disc diffusion method^9-11 at 200 ppm concentration. The antibacterial activity was tested against Xanthomonas citri, Escherichia coli, Erwinia carotovara and Bacillus subtilis using Penicillin as a standard antibiotic. The zone of inhibition was measured using mm scale. (Table-2)

CONCLUSION:

In conclusion, we have synthesized some new secondary amines from Schiff bases by using sodium borohydride, shorter reaction time, simple reaction condition, easy work up and better yield. From the antibacterial screening it was observed that all compounds exhibited antibacterial activity against all organisms employed compound numbers Id, Ie, Ih, Ii and Im showed greater/nearly same antibacterial activity than standard drug penicillin where as other compounds showed moderate to good activity.

ACKNOWLEDGEMENT:

The authors are thankful to principal, Yeshwant Mahavidyalaya, Nanded for providing laboratory facilities and the Director of IICT, Hyderabad for providing spectral analysis. The authors are also thankful to Western Regional office U.G.C. Pune for providing financial support [File No. 47-876/09 (WRO)].

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Received on 11.01.2010 Modified on 17.02.2010

Asian J. Research Chem. 3(3): July- Sept. 2010; Page 578-580