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The structure-activity relationships of (E)-chalcone-4-carboxylic acids, which are retinoidal benzoic acids represented by R-Ph-X-Ph-COOH (4, X = -COCH = CH-), are discussed on the basis of differentiation-inducing activity on human promyelocytic leukemia cells HL-60. The activity was increased by the substitution of a bulky alkyl group(s) (R), and among such compounds, (E)-4-3-(3,5-di-tert-butylphenyl)-3-oxo-1-propenylbenzoic acid (Ch55) and (E)-4-3-oxo-3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1 -propenylbenzoic acid (Ch80) are several times more active than retinoic acid. Though the stable conformer of chalcone derivatives is linear (s-cis form), the conformationally restricted analogue 4-(6,7,8,9-tetrahydro-6,6,9,9-tetramethyl-4H-4-oxonaphtho2,3-bpy ran-2-yl)benzoic acid (Fv80) is more active than Ch80. While the effect of introduction of an oxygen atom varied, 4-1-hydroxy-3-oxo-3-(5,6,7,8-tetrahydro-3-hydroxy-5,5,8,8-tetramethyl-2 - naphthalenyl)-1-propenylbenzoic acid (Re80), regarded as a derivative of Ch80 with two additional hydroxyl groups, has very strong activity.
Kagechika et al. (Sat,) studied this question.