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. Author manuscript; available in PMC: 2016 Mar 21.
Published in final edited form as: Int J Oncol. 2000 May;16(5):971–978. doi: 10.3892/ijo.16.5.971

Table I.

Effect of single structural alterations of caffeine on G2 checkpoint inhibition, solubility and cytotoxicity.

Compound
number		 Structural alteration G2 checkpoint
inhibition (mM)a 		Solubilityb Cytotoxicity
IC50 (mM)c
  1 1-CH3 (caffeine) 0.6 ++ >2
  2 1-H (theobromine) Inactive + 2
  3 1-CH2CH3 0.4 ++ >2
  4 1-CH2CH2CH3 0.2 ++ >2
  5 1-CH2CH2CH2CH2C(O)CH3(pentoxifylline) 0.8 ++ >2
  6 1-CH2OCH3 2 ++ >2
  7 1-CH2CH=CH2 >2 ++ >2
  8 1-CH2C≡CH Inactive ++ >2
  9 1-CH2CN Inactive ++ >2
10 1-CH2C(O)OCH2CH3 Inactive ++ >2
11 1-Benzyl Inactive ++ >2
12 3-H (paraxanthine) Inactive ++ >2
13 3-CH2C≡CH Inactive ++ >2
14 3-CH2CH2CH3 Inactive ++ >2
15 7-H (theophylline) >2 ++ >2
16 7-CH2CH=CH2 Inactive − >2
17 7-CH2C≡CH Inactive + >2
18 7-CH2CH2CH3 >2 ++ >2
19 7-CH2CH2Cl Inactive ++ >2
20 7-CH2CH2OH Inactive ++ >2
21 7-CH2CN Inactive ++ >2
22 7-Benzyl Inactive + 0.4
23 8-Phenyl 0.7 − >2
24 8-Cyclohexyl 0.2 − 0.7
25 8-CH3 0.7 ++ 2
26 8-CF3 Inactive − >2
27 8-Cyclobutyl 0.7 + 0.5
28 8-Br 0.2 + 1
29 8-Chlorostyryl Inactive − 0.05
a

Concentration required to achieve 50% of the maximal G2 checkpoint inhibition elicited by caffeine.

b

++, no precipitates observed at all on concentrations tested; +, precipitates observed at concentrations above 0.5 mM; −, precipitates observed at concentrations below 0.5 mM.

c

Determined by MTT assay as described in Materials and methods.