Technical field : Free radicals play a major role in the progression of a wide range of pathological disorders such as brain disfunction, cancer, cardiovascular disease and inflammation. Free radicals are also found to be responsible for deterioration of food articles during processing and storage. Addition of antioxidants and free radical scavengers to processed foods reduce the harmful effects of free radicals. Antioxidants and superoxide scavengers are also found to control the harmful effect of free radicals in biological systems.

3,4', 5-trihydroxystilbene commonly known as resveratrol is found in grapes. Resveratrol is found to exhibit antioxidative and antimutagenic properties. Resveratrol is also an inducer of phase II drug metabolizing enzymes. In humans, resveratrol consumption is found to inhibit peroxidation of plasma low density lipoprotein and this effect has been proposed to protect against the development of atherosclerosis. The above referenced bioprotective properties of resveratrol are attributed to the presence of phenolic groups in its structure. Naturally occurring resveratrol of the formula given below is found to exhibit better bioprotective activity than the corresponding methylated derivatives. OH 5 lez Resveratrol Background Art: Antioxidant and superoxide scavenging properties of resveratrol have been scientifically established. Efforts are being made to synthesise structural analogs of resveratrol for evaluation of their relative antioxidant potentials.

Disclosure of the invention: It has now been found that novel resveratrol analogs of the general formula I show improved and better antioxidative action than the naturally occuring resveratrol. Enhanced activity of these compounds may be due to the presence of catechol, pyrogallol moieties or a combination of these in their structure.

This invention relates to novel resveratrol analogs of the formula I wherein R, Rl, R2 and R3 are : 1. R=OH, Rl=R2=R3=H ; 2. R=OH, R1=Br, R2=R3=H ; 3. R=Ri=OH, R2-R3=H ; 4. R=Ri=R3-H, Rz= 3,4, 5-trihydroxybenzoyl; 5. R=R1=H, R2=R3=3, 4,5-trihydroxybenzoyl ; 6. R=R1=R3=H, R2= 3,4-dihydroxycinnamoyl ; 7. R=R1=R3=H, R2=3,4, 5-trihydroxycinnamoyl ; 8. R=Rl=R3=H, R2=-CH2CH2N (CH3) 2; 9. R=R1=R3=H, R2= -COCH2NH2.HCl Prefered compounds of the invention are (1) 5-[(1E)-2-(3, 4-dihydroxyphenyl) vinyl]-benzenel, 2,3-triol, 1 (2) 5-[(1E)-2-(5-Bromo-3, 4-dihydroxyphenyl) vinyl]-benzenel, 2, 3-triol, 2 (3) 5- [ (lE)-2- (3, 4,5-trihydroxyphenyl) vinyl]-benzenel, 2,3-triol, 3 (4) 5-[(1E)-2-(4-hydroxyphenyl)vinyl]-3-hydroxyphenyl 3, 4,5-trihydroxy- benzoate, 4 (5) 3- [ (lE)-2- (4-hydroxyphenyl) vinyl]-5- (3, 4, 5trihydroxyphenylcarbonyloxy)- phenyl 3,4, 5-trihydroxybenzoate, 5 (6) 5- [ (IE)-2- (4-hydroxyphenyl) vinyl] -3-hydroxyphenyl (2E) -3 (3,4-dihydroxy- phenyl) prop-2-enoate, 6 (7) 5- [ (lE)-2- (4-hydroxyphenyl) vinyl] -3-hydroxyphenyl (2E) 3 (3, 4,5- trihydroxyphenyl) prop-2-enoate, 7 (8) 3- [ (lE)-2- (4-hydroxyphenyl) vinyl]-5- [2- (dimethylamino) ethoxy] phenol, 8 (9) 5- [ (IE)-2- (4-hydroxyphenyl) vinyl] -3-hydroxyphenyl 2-aminoacetate hydrochloride, 9.

Novel compounds of this invention may be prepared by the following processes.

Compounds represented by 1,2 and 3 may be prepared by Wittig-Horner reaction. Substituted benzyl phosphonate may be reacted with methoxy substituted benzaldehyde in the presence of sodium hydride. Demethylation may be effected by treating with pyridine hydrochloride resulting in compounds 1, 2 and 3. This reaction scheme is shown hereinafter. M13 \ OCHy )-IyCO/CFIO FIyCO Fl3CO toCZHsh NaH Hyoo/ I/ H3CO H3CO OCH3 Hypo \ R y R 180-190°C Pyridine hydrochloride H H SCHEME oil Ho lao R I ro R 1. R=ll, dihydroxyresveratrol 2. R=Br, dihydroxybromoresveratrol 3. R=OH, trihydroxyresveratrol SCHEME 2 Compounds represented by 4, 5, 6, 7, 8 and 9 may be prepared by 1, 3- dicyclohexylcarbodiimide coupling of protected resveratrol, with corresponding acids or alkyl halides. The condensation product is subjected to debenzylation in the presence of aluminium chloride to produce compounds indicated by 4, 5, 6, 7, 8 and 9. This reaction is represented by the reaction scheme 2 shown below. ol R3 H Benzyl bromide, K2CO3, Acetone "OR, t /ou Bn0 HO 10, R3=benzyl, R4= H 11, R3=R4=H RCOOH/RCl 1, 3-dicyclohexylcarbo- diimide, 4- (dimethylamino pyridine ORs Ri Ail3, N, N-dimethyl- aniline, CH2CI2 OR6 OR2 BnO HO 4 Rl=H, R2=3, 4, 5-trihydroxybenzoyl 12 R6=3, 4, 5-tribenzyloxybenzoyl, Rs=benzyl 5 R [=R2-3, 4. 5-trilIydroxybenzoyl 13 RS=R6=3, 4, 5-tribenzyloxybenzoyl 6 RiH 14 R6=3, 4-dibenzyioxycinnamoyi, R5=benzyl 7 R, R2=3, 4, 5-trihydroxycinnamoyl 15 R6=3, 4, 5-tribenzyloxycinnamoyl, R5=benzyl 8 R) =H. R2=-CH2CH2N (CH3) 2 16 R6=-CH2CH, N (CH3) 2, Rs=benzyl 9 Rl= H, R2=-OCCH, NH2. HCI 17 R6=-OCCHNHBOC, R=benzyl The final product obtained has the following substituents from the reaction scheme 2 as shown below: 4. Rl=H, R2= 3,4, 5-trihydroxybenzoyl ; 5. Rl= R2=3, 4,5-trihydroxybenzoyl ; 6. Rl=H, R2= 3, 4-dihydroxycinnamoyl; 7. Rl=H, R2=3,4, 5-trihydroxycinnamoyl ; 8. Rl=H, R2=-CH2CH2N (CH3) 2 ; 9. Rl=H, R2=-COCH2NH2. HC1 This invention also includes processes for preparing novel resveratrol analogs.

One such process comprises subjecting diethyl 3,4, 5- trimethoxybenzylphosphonate with 3,4-dimethoxybenzaldehyde or 5-bromo- 3, 4-dimethoxybenzaldehyde or 3,4, 5-trilnethoxybenzaldehyde in presence of NaH to give 1-(3,4-dimethoxyphenyl)-2-(3, 4, 5-trimethoxyphenyl) ethylene or 1- (5-bromo-3, 4-dimethoxyphenyl)-2- (3, 4,5-trimethoxyphenyl) ethylene or 1,2- bis (3,4, 5-trimethoxyphenyl) ethylene. These compounds may be demethylated in the presence of pyridine hydrochloride to get analogs of resveratrol shown as compounds of 1, 2 and 3.

Preferred embodiments relating to the different processes of preparing resveratrol analogs of the subject invention are illustrated in the examples given below.

Example 1 5-[(1E)-2-(3,4,5-trihydroxyphenyl)vinyl]-benzene1,2,3-triol, 3 To an ice cold solution of sodium hydride (0.57 g, 12 mmol) in dry tetrahydrofuran (10 mL) was added 3,4, 5-trimethoxybenzylphosphonate ester (3.2 g, 10 mmol) in THF (5 mL) via syringe for 15 min. The solution was slowly allowed to rt and stirred for 15 min. After cooling the solution was added 3,4, 5-trimethoxybenzaldehyde (1.3 g, 7 mmol) in THF (5 mL) and stirred at ice cold temperature for 2 hrs and at rt for 2 hrs. Methanol (2 mL) was added to destroy the excess sodium hydride, diluted with ice cold water and acidified with dil HCI. The solution was extracted with chloroform and the organic layer was washed with water, sodium bicarbonate, brine and dried over sodium sulfate. The residue obtained after evaporation of the solvent was chromatographed over silica gel column to give 1, 2-bis (3,4, 5- trimethoxyphenyl) ethylene, m. p. 218-220°C ; IR (KBr) Vma, 2931, 2827,1586, 1506,1454, 1247,1121, 987,824 cm~l ; 1H NMR (CDC13, 400 MHz) 8 6.94 (2H, s), 6.74 (4H, s), 3.92 (12H, s), 3.87 (6H, s).

Demethylation: A mixture of 1, 2-bis (3,4, 5-trimethoxyphenyl) ethylene (1.0 g) and pyridine hydrochloride (5.0 g) was heated with stirring at 180-190°C for 4 hrs. After cooling to room temperature the reaction mixture was diluted with ice water, acidified with dil HC1 and extracted with ethyl acetate thrice. The combined ethyl acetate layer was washed with water, brine and dried over sodium sulfate. The residue obtained after evaporation of the solvent was chromatographed over silica gel column eluting with chloroform-methanol to give 3, m. p. 242-244°C ; IR (KBr) vma, 3466,1614, 1531, 1318, 1179,1013, 956, 830 cm-1; 1H NMR (CH3OD, 400 MHz) # 6.47 (2H, s), 6.32 (4H, s).

Example: 2 5-[(1E)-2-(3,4-dihydroxyphenyl)vinyl]-benzene1,2, 3-triol, 1 Reaction of diethyl 3, 4, 5-trimethoxybenzylphosphonate (5. 4 g, 17 mmol) with 3, 4-dimethoxybenzaldehyde (2 g, 12 mmol) in presence of NaH (0.97 g, 20 mmol), under the conditions noted in example 1, gave 1- (3, 4- dimethoxyphenyl)-2- (3, 4,5-trimethoxyphenyl) ethylene, m. p. 150-152 °C ; IR (KBr) vmax 2934,2835, 1583,1510, 1331,1249, 1125,1024, 1004,976, 850 cm ; HNMR (CDCl3, 400 MHz) 8 7.06 (1H, s), 7.05 (1H, dd, J= 8.0, 1.9 Hz), 6.97 (1H, d, J=16.0 Hz), 6.89 (1H, d, J= 16. 0 Hz), 6.87 (1H, d, J= 8.0 Hz), 6.73 (2H, s), 3.95 (3H, s), 3.92 (6H, s), 3.91 (3H, s), 3.87 (3H, s).

Demethylation: The 1- (3, 4-dimethoxyphenyl)-2- (3, 4,5-trimethoxyphenyl) ethylene (1.3 g) on demethylation with pyridine hydrochloride (7 g) under the conditions noted in example 1 gave 1, m. p. 222-224 °C ; IR (KBr) Vmax 3450, 3338,1608, 1535,1449, 1320,1177, 1119,1035, 956,848, 797 cm~l, tHNMR (CH30D, 400 MHz) 5 6.76 (1H, s), 6.61 (1H, d, J= 8. 0 Hz), 6.55 (1H, d, J=16.0 Hz), 6.54 (1H, d, J= 8.0 Hz), 6.50 (1H, d, J= 16.0 Hz), 6.33 (2H, s).

Example: 3 5-[(1E)-2-(5-Bromo-3,4-dihydroxyphenyl)vinyl]-benzenel, 2,3-triol, 2 Reaction of diethyl 3,4, 5-trimethoxybenzylphosphonate (2.7 g, 8 mmol) with 5 bromo-3,4-dimethoxybenzaldehyde (1.5 g, 6 mmol) in presence of NaH (0. 5 g, 10 mmol) under the conditions noted in example 1, gave 1- (5-bromo- 3, 4-dimethoxyphenyl)-2- (3, 4,5-trimethoxyphenyl) ethylene, m. p. 180-182 °C ; IR (KBr) may 3000, 2939,1582, 1555,1509, 1492,1418, 1347,1277, 1249, 1126,1044, 998,962, 840 cm~l ; lH NMR (CDC13, 400 MHz) 5 7.30 (1H, d, J=1.8 Hz), 6.97 (1H, d, J= 1.8 Hz), 6.95 (1H, d, J=16.2 Hz), 6.87 (1H, d, J= 16.2 Hz), 6.72 (2H, s), 3.93 (3H, s), 3.92 (6H, s), 3.87 (6H, s).

Demethylation : The 1- (5-bromo-3, 4-dimethoxyphenyl)-2- (3, 4,5- trimethoxyphenyl) ethylene (1.3 g) on demethylation with pyridine hydrochloride (7 g) under the conditions noted in example 1 gave 2, m. p. 148 °C ; IR (KBr) vmax 3450,1610, 1536,1461, 1431,1340, 1291,1191, 1038,997, 954, 842, 799 cm-1; 1 NMR (DMSO-d6, 400 MHz) 6 9.81 (1H, s), 9.21 (1H, s), 8.88 (2H, s), 8.30 (1H, s), 7.13 (1H, s), 6.93 (1H, s), 6.72 (1H, d, J=16. 2 Hz), 6.64 (1H, d, J= 16.2 Hz), 6.47 (2H, s).

Example : 4 5-[(1E)-2-(4-hydroxyphenyl)vinyl]-3-hydroxyphenyl 3,4, 5-trihydroxybenzoate, 4.

3, 4'-Dibenzyloxyresveratrol (10) : To a mixture of resveratrol (5.0 g, 22 mmol), potassium carbonate (12.5 g, 91 mmol) in acetone (100 mL) was added benzyl bromide (5.5 mL, 46 mmol) and the mixture was stirred at rt for 14 hr.

The solids were filtered off and the solvent was removed under reduced pressure. The residue obtained was chromatographed over silica gel column eluting with a mixture of pet. ether-ethyl acetate (80: 20), gave 10 (2.2 g, 25%), which was recrystallised from chloroform-hexane, m. p. 144-146 °C; IR (Neat) vmax3376, 1595,1505, 1445,1257, 1153,1019, 963,835, 771 cni l.

1- (Tribenzyloxybenzoyl)-3, 4'-dibenzyloxyresveratrol (12): To a solution of dibenzyloxyresveratrol (10,0. 5 g, 1.23 mmol) in dichlorometahne (25 mL) were added sequentially 3,4, 5-tribenzyloxybenzoic acid (0.645 g, 1.47 mmol), DMAP (catalytic) and then DCC (0.5 g, 2.45 mmol) at rt. The reaction mixture was stirred at the same temperature for 14 hrs and the solid was filtered. The solution was diluted with chloroform and washed with water, 2% aq. acetic acid, 1% sodium bicarbonate, brine and dried over sodium sulfate. The residue obtained after evaporation of the solvent was chromatographed over silica gel column eluting with chloroform-hexane, gave 12 (0.9 g, 90%), m. p. 158-160 °C ; IR (Neat) vm 2925,1731, 1594,1504, 1434,1332, 1237,1194, 1123,1021, 743,699 cni i.

1-O-Galloylresveratrol (4): To a mixture of 1- (tribenzyloxybenzoyl)-3, 4'- dibenzyloxyresveratrol (12,0. 5 g, 0.6 mmol), N, N,-dimethylaniline (3.2 mL, 25 mmol) and CH2C12 (25 mL), was added aluminium chloride (1.8 g, 13.5 mmol) at 0-5°C and the reaction mixture was slowly brought to rt and stirred at rt for 6 h. The reaction mixture was quenched with 1N HC1 (25 mL) and extracted with ethyl acetate (2 x 25 mL). The combined organic layer was washed with water, brine and dried over sodium sulfate. The residue obtained after removal of the solvent was purified by column chromatography over silica gel column using mixtures of chloroform-methanol (90: 10) as eluent to give 4 (110 mg, 48%), which was crystallised from chloroform-methanol, m. p. 254-256 °C, IR (KBr) Umax 3410,1700, 1612,1449, 1378,1235, 1144,1038 cri 1 ; 1H NMR (CH30D, 400 MHz) 8 7.21 (2H, d, J= 7.75 Hz), 7.03 (2H, s), 6.88 (1H, d, J=16.25 Hz), 6.72 (1H, d, J=16. 28 Hz), 6.67 (1H, s), 6.62 (1H, s), 6.60 (2H, d, J=8.29 Hz), 6.30 (1H, s).

Example: 5 3-[(1E)-2-(4-hydroxyphenyl)vinyl]-5-(3, 4, 5-trihydroxyphenylcarbonyloxy)- phenyl 3,4,5-trihydroxybenzoate, 5 1,3-Di-(tribenzylopxybenzoyl)-4'-benzyloxyresveratrol (13): Reaction of monobenzyloxy resveratrol (11,0. 5 g, 1.57 mmol), with 3,4, 5- tribenzyloxybenzoic acid (1.66 g, 3.77 mmol), in the presence of DMAP (catalytic) and DCC (1.29 g, 6.28 mmol) under the conditions noted in example 4 gave 13 (1.4 g, 77%), m. p. 180-182 °C ; IR (KBr) VmaX 3031, 1732,1590, 1505, 1428,1381, 1333,1188, 1122,1003, 859,748, 696 cm~l.

1, 3-O-Digalloylresveratrol (5): Reaction of 1, 3-di- (tribenzyloxybenzoyl)-4'- benzyloxyresveratrol (13,1. 4 g, 1.2 mmol) with N, N,-dimethylaniline (6.4 mL, 50 mmol) and aluminium chloride (4.8 g, 36 mmol) under the conditions noted in example 4 gave 5 (100 mg, 16%), which was crystallised from chloroform- methanol, m. p. 210-212 °C, IR (KBr) umax 3404,1710, 1606,1514, 1453,1383, 1350, 1202,1129, 1041,997, 953,753 cm~l ; 1H NMR (CH30D, 400 MHz) 8 7.35 (2H, d, J= 8.5 Hz), 7.18 (1H, s), 7.17 (1H, s), 7.14 (4H, s), 7.10 (1H, d, J=16.0 Hz), 6.93 (1H, d, J=16.0 Hz), 6.81-6. 83 (1H, m), 6.70 (2H, d, J=8.5 Hz).

Example: 6 <BR> <BR> <BR> <BR> <BR> 5 [ (IE)-2- (4-hydroxyphenyl) vinylJ-3-hydroxyphenyl (2E)-3- (3, 4-dihydroxy- phenyl) prop-2-enoate, 6 1-(3,4-Dibenzyloxycinnamoyl)-3,4'-dibenzyloxyreseveratrol (14): Reaction of dibenzyloxy resveratrol (10,0. 2 g, 0.49 mmol) with 3,4-dibenzyloxycinnamic acid (0.212 g, 0.59 mmol) in presence of DMAP (catalytic) and DCC (0.2 g, 0.98 mmol) under the conditions noted in example 4 gave 14 (0.32 g, 87%), m. p. 122-124 °C ; IR (Neat) Vma 3032, 2926,1724, 1630,1599, 1510,1453, 1383,1250, 1133,1022, 843,736, 697 cm-1.

1-0- (3, 4-Dihydroxycinnamoyl) resveratrol (6): Reaction of 1- (3, 4- dibenzyloxycinnamoyl)-3, 4'-dibenzyloxyresveratrol (14,0. 3 g, 0.4 mmol) with N, N, -dimethylaniline (2 mL, 1.8 mmol) and aluminium chloride (1.2 g, 9.0 mmol) under the conditions noted in example 4 gave 6 (55 mg, 35%), which was crystallised from chloroform-methanol, m. p. 216-220 °C, IR (KBr) Umax 3338, 1709,1637, 1602,1514, 1384, 1277,1173, 1152,982, 961, 846 cm-1; 1H NMR (DMOS-d6, 400 MHz) 6 9.74 (2H, s, Ar-OH), 9.62 (1H, s, Ar-OH), 9.23 (1H, s, Ar-OH), 7.68 (1EI, d, J= 15.9 Hz), 7.43 (2H, d, J= 8.1 Hz), 7.14 (1EI, d, J= 8. 0 Hz), 7.12 (1H, d, J= 8.0 Hz), 7.11 (1H, d, J= 16.2 Hz), 6.94 (1H, d, J= 16. 2 Hz), 6.82 (2H, s), 6.80 (1H, s), 6.78 (2H, d, J= 8.0 Hz), 6.50 (1H, d, J=15.9 Hz), 6.45 (1H, s).

Example : 7 5-[(1E)-2-(4-hydroxyphenyl)vinyl]-3-hydroxyphenyl (2E)-3-(3,4,5-trihydroxy- phenyl) prop-2-enoate, 7 1- (3, 4, 5-Tribenzyloxycinnamoyl)-3, 4'-dibenzyloxyresveratrol (15): Reaction of dibenzyloxyresveratrol (10,0. 5 g, 1.23 mmol) with 3,4, 5-tribenzyloxy- cinnamic acid (0.69 g, 1.47 mmol) in presence of DMAP (catalytic) and DCC (0.5 g, 2.45 mmol) under the conditions noted in example 4, gave 15 (0.8 g, 76%), m. p. 130-132 °C ; IR (Neat) vmax 3032,2929, 1726,1630, 1582,1506, 1432, 1382, 1271, 1246,1136, 1027,827, 737,697 cm-1.

1-0- (3, 4, 5-Trihydroxycinnamoyl) resveratrol (7): Reaction of 1- (3, 4,5- tribenzyloxycinnamoyl)-3, 4'-dibenzyloxyresveratrol (15,0. 75 g, 0.88 mmol) with N, N,-dimethylaniline (5.0 mL, 40 mmol) and aluminium chloride (3.0 g, 22 mmol) under the conditions noted in example 4, gave 7 (150 mg, 42%), which was crystallised from chloroform-methanol, m. p. 210-212 °C, IR (KBr) umax 3366,1711, 1635,1603, 1515,1449, 1292,1172, 1149,1031, 995,963, 835 cm~l ; 1H NMR (DMSO-d6, 400 MHz) 6 9.75 (1H, s, Ar-OH), 9.63 (1H, s, Ar-OH), 9.22 (2H, s, Ar-OH), 8.94 (1H, s, Ar-OH), 7.59 (1H, d, J= 15.8 Hz), 7.43 (2H, d, J= 8.5 Hz), 7.11 (1H, d, J= 16.4 Hz), 6.94 (1H, d, J= 16.4 Hz), 6.83 (1H, s), 6.82 (1H, s), 6.77 (2H, d, J= 8.4 Hz), 6.70 (2H, s), 6.44 (1H, s), 6.39 (1H, d, J= 15.8 Hz).

Example: 8 3-[(1E)-2-(4-hydroxyphenyl)vinyl]-5-[2-(dimethylamino)ethoxy ] phenol, 8 1- (N, N-Dimethylaminoethyl)-3, 4'-dibenzyloxyresveratrol (16): To a solution of dibenzyloxy resveratrol (10,0. 5 g, 1.23 mmol) in acetone (50 mL) were added sequentially, potassium carbonate (0.85 g, 6.13 mmol) and N, N-dimethyl aminoethyl HCl (0.36 g, 2.45 mmol) at rt. The reaction mixture was refluxed for 5 hrs. The solids were filtered and the residue obtained after evaporation of the solvent was chromatographed over silica gel column eluting with 5% chloroform-methanol, gave 16 (0.5 g, 85%),; IR (Neat) vmax 3064,3031, 2936, 1595, 1510, 1453,1297, 1248,1162, 1054,962, 832,741, 698 cm~l.

1-O-(N, N-Dimethyl aminoethyl) resveratrol (8): Reaction of 1-(N,N- dimethyl aminoethyl)-3, 4'-dibenzyloxyresveratrol (16,0. 6 g, 1.25 mmol) with N, N, -dimethylaniline (1.0 mL) and aluminium chloride (0. 7 g, 5.0 mmol) under the conditions noted in example 4, gave 8 (110 mg, 29%), which was crystallised from chloroform-methanol, m. p. 92-94 °C, IR' (KBr) umax 3410, 2927,1587, 1512,1455, 1384,1267, 1166,1016, 962,837 crn7' ;'H NMR (DMSO-d6,400 MHz) 8 9.58 (1H, br s, Ar-OH), 9.41 (1H, br s, Ar-OH), 7.41 (2H, d, J= 8.5 Hz), 7.05 (1H, d, J=16.3 Hz), 6.88 (1H, d, J=16.3 Hz), 6.77 (2H, d, J=8.5 Hz), 6.59 (1H, s), 6.53 (1H, s), 6.23 (1H, s), 4.04 (2H, t, J=5. 7 Hz), 2.68 (2H, t, J=5.6 Hz), 2.26 (6H, s).

Antioxidant (superoxide scavenging) activity of these compounds are determined by conventional methods like McCord and Fridovich method, which is based on light induced superoxide generation by riboflavin and corresponding reduction of NBT. The assay mixture contains phosphate buffer, EDTA, NBT and riboflavin. Different concentrations of these compounds were assessed and their optical densities measured before and after illumination. The percentage value of inhibition of superoxide production by the compounds of this invention was evaluated and compared with the absorbance value of control and experimental data.

The compounds of this invention are found to show better bioprotective activity like superoxide scavenging (Table-I and Fig-1 ; Superoxide scavenging activity is expressed in IC50 values, lower the IC50 value, higher is the activity).

Though the processes for preparation of the novel compounds of this invention have been disclosed hereinabove as specific embodiments, alternate processes known to persons skilled in the art are not excluded from the scope of this invention.

Table-I Superoxide scavenging activity (NBT) S. No Compound IC50 ( 1 Resveratrol 106.0 2 1 3. 0 3 2 8. 1 4 3 0. 9 5 4 16. 0 6 5 17. 5 7 6 9. 2 8 7 10.0 9 8 34. 1 10 9 29. 3 ICso : 50% Inhibitory Concentration; Lower the IC50 value, higher is the antioxidant activity.