Table 2 IR and 1H NMR spectroscopic data for the compounds 2a–l and 3a–k
Compound νmax (KBr)/cmϪ1
δH [60 MHz; (CD3)2SO; Me4Si]
2a
2b
2c
3370, 3160 (NH)
3380, 3210 (NH)
3410, 3180 (NH)
7.32 (2 H, dd, JH,H 8.8, JH,F 9.1, Ar-mH), 8.06 (2 H, dd, JH,H 8.8, JH,F 5.5, Ar-oH), 8.46 (1 H, s, N᎐CHAr),
8.55 (2 H, s, 2- and 8-H), 12.50 (2 H, br s, 2 × NH)
᎐
3.85 (3 H, s, OMe), 7.05 (2 H, d, J 8.8, Ar-mH), 8.00 (2 H, d, J 8.8, Ar-oH), 8.52 (1 H, s, N᎐CHAr), 8.63
᎐
(1 H, s, 2-H), 8.65 (1 H, s, 8-H), 12.90 (2 H, br s, 2 × NH)
0.95 (3 H, t, J 6.8, CHCH2CH2CH3), 1.26–1.84 (2 H, m, CHCH2CH2CH3), 2.25–2.57 (2 H, m, CHCH2-
CH2CH3), 7.51 (1 H, br t, J 6.2, CHCH2CH2CH3), 8.34 (1 H, s, 8-H), 11.74 (1 H, s, NH), 12.24 (1 H, br s,
NH)
2d
2e
2f
3400, 3200 (NH)
3450, 3200 (NH)
3350, 3200 (NH)
3420, 3200 (NH)
3350, 3200 (NH)
3350, 3200 (NH)
7.33–7.66 (3 H, m, Ph-m,pH), 7.73–8.13 (2 H, m, Ph-oH), 8.27 (1 H, s, N᎐CHPh), 8.43 (1 H, s, 8-H), 12.15
(2 H, br s, 2 × NH)
᎐
7.31 (2 H, dd, JH,H 8.8, JH,F 8.8, Ar-mH), 7.99 (2 H, dd, JH,H 8.8, JH,F 5.3, Ar-oH), 8.25 (1 H, s, N᎐CHAr),
᎐
8.42 (1 H, s, 8-H), 12.13 (2 H, br s, 2 × NH)
7.51 (2 H, d, J 8.8, Ar-mH), 7.94 (2 H, d, J 8.8, Ar-oH), 8.25 (1 H, s, N᎐CHAr), 8.42 (1 H, s, 8-H), 12.16
᎐
(2 H, br s, 2 × NH)
2g
2h
2i
3.83 (3 H, s, OMe), 7.03 (2 H, d, J 8.8, Ar-mH), 7.87 (2 H, d, J 8.8, Ar-oH), 8.20 (1 H, s, N᎐CHAr), 8.38
᎐
(1 H, s, 8-H), 12.00 (2 H, s, 2 × NH)
3.00 (6 H, s, NMe2), 6.75 (2 H, d, J 8.8, Ar-mH), 7.73 (2 H, d, J 8.8, Ar-oH), 8.13 (1 H, s, N᎐CHAr), 8.35
᎐
(1 H, s, 8-H), 11.83 (2 H, s, 2 × NH)
6.12 (2 H, s, OCH2O), 6.97 (1 H, d, J5Ј,6Ј 8.2, 5Ј-H), 7.21 (1 H, dd, J5Ј,6Ј 8.2, J2Ј,6Ј 1.8, 6Ј-H), 7.80
(1 H, d, J2Ј,6Ј 1.8, 2Ј-H), 8.15 (1 H, s, N᎐CHAr), 8.39 (1 H, s, 8-H), 12.01 (2 H, s, 2 × NH)
᎐
2ja
2k
3410, 3200 (NH)
3410, 3190 (NH)
8.07 (2 H, d, J 8.8, Ar-oH), 8.46 (2 H, d, J 8.8, Ar-mH), 8.54 (1 H, s, N᎐CHAr), 9.45 (1 H, s, 8-H)
᎐
6.87 (2 H, d, J 8.2, Ar-mH), 7.76 (1 H, d, J 8.2, Ar-oH), 8.16 (1 H, s, N᎐CHAr), 8.37 (1 H, s, 8-H), 9.89 (1 H,
᎐
s, OH), 11.90 (2 H, s, 2 × NH)
21
3370, 3320, 3190 (NH)
3.82 (3 H, s, OMe), 5.86 (2 H, br s, NH2), 7.00 (2 H, d, J 8.8, Ar-mH), 7.75 (2 H, d, J 8.8, Ar-oH), 7.90 (1 H,
s, N᎐CHAr), 8.22 (1 H, s, 8-H), 11.30 (2 H, br s, 2 × NH)
᎐
3a
3b
3c
3d
3060 (NH)
3040 (NH)
3070 (NH)
3070 (NH)
8.36 (1 H, s, 8-H), 9.27 (1 H, s, 5-H), 9.41 (1 H, s, 3-H), 13.94 (1 H, br s, NH)
8.39 (1 H, s, 8-H), 9.51 (1 H, s, 3-H), 12.21 (1 H, br s, NH)
2.97 (3 H, s, Me), 8.33 (1 H, s, 8-H), 12.00 (1 H, br s, NH)
1.05 (3 H, t, J 7.3, CH2CH2CH3), 1.72–2.10 (2 H, m, CH2CH2CH3), 3.37 (2 H, t, J 7.1, CH2CH2CH3), 8.32
(1 H, s, 8-H), 12.30 (1 H, br s, NH)
3e
3f
3020 (NH)
3030 (NH)
7.50–7.76 (5 H, m, Ph-H), 8.41 (1 H, s, 8-H), 12.13 (1 H, br s, NH)
7.39 (2 H, dd, JH,H 8.8, JH,F 8.8, Ar-mH), 7.79 (2 H, dd, JH,H 8.8, JH,F 5.3, Ar-oH), 8.42 (1 H, s, 8-H), 12.07
(1 H, br s, NH)
3g
3050 (NH)
3.86 (3 H, s, OMe), 7.09 (2 H, d, J 8.8, Ar-mH), 7.63 (2 H, d, J 8.8, Ar-oH), 8.40 (1 H, s, 8-H), 12.02 (1 H,
br s, NH)
8.94 (1 H, s, 8-H), 9.67 (1 H, s, 3-H)
3ha
3ia
3ja
3k
3320, 3280, 3100 (NH)
3310, 3100, 3060 (NH)
3300, 3120, 3070 (NH)
3300, 3170, 3100 (NH)
2.64 (3 H, s, Me), 8.93 (1 H, s, 8-H)
7.63–7.87 (3 H, m, Ph-m,pH), 8.15–8.38 (2 H, m, Ph-oH), 8.94 (1 H, s, 8-H)
3.86 (3 H, s, OMe), 7.12 (2 H, d, J 8.8, Ar-mH), 7.58 (2 H, br s, NH2), 8.22 (2 H, d, J 8.8, Ar-oH), 8.47 (1 H,
s, 8-H), 12.09 (1 H, br s, NH)
a In CF3CO2D.
6-hydrazino derivative 5a and 5b with appropriate triethyl
orthoesters (40–60 parts) under reflux afforded the correspond-
ing 5-oxo- 7a–c and 5-thioxo-triazolopurines 7f–h in ca. 60%
yields. The intramolecular cyclisation of 6b,c,i to the corres-
ponding 7d,e,i (ca. 60% yields) were also accomplished by oxi-
dation using lead tetraacetate (1.5 equiv.) in 1,4-dioxane at
120 ЊC in a similar manner as above. All new compounds 6a–l
and 7a–i were fully characterised by various spectral analyses
and satisfactory elemental combustion analyses as given in
Tables 3 and 4. It is noteworthy that the compounds 3b–k and
7a–i were reasonably stable in acid or alkali solution due to the
substituents at the 5-position.
derivatives 2d–i,k with a chloro group showed more inhibitory
properties than allopurinol. On the other hand, the triazolo-
purines 3a,b,e,g–k gave poor activities.
Oxypurinol (4,6-dioxopyrazolopyrimidine), which is a struc-
tural isomer of xanthine (2,6-dioxopurine), forms very tightly a
reversible complex with electronically reduced xanthine oxidase
due to the 6-oxo group as compared to allopurinol (4-oxo
derivative).32 Therefore, in order to investigate whether the
inhibitory activity is reinforced by incorporating an oxo group
at the 2-position of the purine ring, we synthesized the 2-oxo
derivatives 6a–g with 6-arylmethylidenehydrazino groups. As
we would expect, all of them showed remarkable potent in-
hibitory activities, being three orders of magnitude more active
than allopurinol. Among them, compound 6b (X = O, R =
4-ClC6H4) (IC50: 0.025 µM) was the most active; it exhibited
970-fold more potent bovine milk XO inhibitory activity than
that of allopurinol (IC50: 24.30 µM). In the case of the 6-
thioxopurines 6h–l, the inhibitory activities were less effective
than the 6-oxopurines 6a–g, but still showed several ten to
hundred times greater activities than that of allopurinol. In
contrast to the above purine derivatives, the triazolopurines
7a–i generally showed more potent inhibitory activities than
that of allopurinol, but less inhibitory activities compared with
the purines 6a–l, and yet some of them showed greater activity,
e.g. compound 7d (X = O, R = 4-ClC6H4) showed 370-fold
(IC50: 0.066 µM) more potent inhibitory activity than allo-
purinol. It was demonstrated that the oxo or thioxo group at
the 2-position and the alkyl or arylmethylidenehydrazino group
at the 6-position of the purines and the oxo or thioxo group at
Xanthine oxidase inhibitory results
The novel purine derivatives (2, 6) and triazolopurine deriva-
tives (3, 7) prepared in this study were tested as inhibitors of
bovine milk xanthine oxidase by a similar assay method to
that previously reported.13 The inhibition (%) and IC50 (µM)
values of tested compounds against bovine milk xanthine
oxidase are listed in Table 5. The introduction of arylaldehyde
hydrazones at the 6-position of 7H-purine markedly increased
their activities as inhibitors of xanthine oxidase, being one
or two orders of magnitude more active than allopurinol.
That is, the values of IC50 for 2a and 2b are 0.528 and 0.236 µM,
respectively, while allopurinol is 24.3 µM. Moreover, the
derivatives substituted by a chloro or amino group at the 2-
position, i.e. compounds 2c–l, showed a tendency to decrease
the activity, but most of the 6-arylmethylidenehydrazino
3120
J. Chem. Soc., Perkin Trans. 1, 1999, 3117–3125