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Conformationally restricted retinoids
Abstract:
A series of conformationally restricted retinoids was synthesized and screened in two assays used to measure the ability of retinoids to control cell differentiation, namely, the reversal of keratinization in tracheal organ culture from vitamin A deficient hamsters and the inhibition of the induction of mouse epidermal ornithine decarboxylase by a tumor promoter. These compounds had bonds corresponding to selected bonds of the E-tetraene chain of retinoic acid (1) held in a planar cisoid conformation by inclusion in an aromatic ring. The meta-substituted analogue 3 of 4-[(E)-2-methyl-4-(2,6,6-trimethylcyclohexenyl)-1,3-butadienyl+ ++]benzoic acid (2) was far less active than 2 in both assays. In contrast, the vinyl homologue of 2 (4) and the 7,8-dihydro and 7,8-methano analogues (5 and 6) had activity comparable to that of 2. Analogues of 4-[(E)-2-(1,1,4,4-tetramethyl-1,2,3,4-tetrahydro-6-naphthyl)propenyl] benzoic acid (7) were also screened. Replacement of the tetrahydronaphthalene ring of 7 by a benzonorbornenyl group (9) significantly reduced activity, as did removal of the vinylic methyl group from 9 (10). Replacement of the propenyl group of 9 by a cyclopropane ring (12) also reduced activity. Replacement of the tetrahydronaphthalene ring of 7 by 4,4-dimethyl-3,4-dihydro-2H-1-benzopyran and -benzothiopyran rings (13 and 14) also decreased activity. Inclusion of the 7,9 double bond system of 1 in an aromatic ring (15 and 16) reduced activity, whereas inclusion of the 5,7 double bond system in an aromatic ring enhanced activity (7 and 19). Inclusion of the 11,13 and 9,11,13 double bond systems in aromatic rings (2 and 18) also reduced activity below that of 1. Retinoic acid, 7, 13, 14, and 19 inhibited papilloma tumor formation in mice. Toxicity testing indicated that 7 was more toxic than 1, 13, 14, and 19, 19 was more toxic than 1, and 13 and 14 were less toxic than 1.
Insights
Researchers synthesized conformationally restricted retinoids to study cell differentiation and tumor formation. Some analogues showed potent activity and reduced toxicity compared to retinoic acid, offering potential therapeutic benefits.
Area of Science:
- Medicinal Chemistry
- Organic Synthesis
- Dermatology
- Oncology
Background:
- Retinoids are crucial for regulating cell differentiation and proliferation.
- Understanding structure-activity relationships of retinoids is key to developing targeted therapies.
- Vitamin A deficiency impacts epithelial cell differentiation, leading to keratinization.
Purpose of the Study:
- To synthesize and evaluate novel, conformationally restricted retinoids.
- To assess the compounds' efficacy in controlling cell differentiation and inhibiting tumor promotion.
- To determine the toxicological profiles of synthesized retinoids.
Main Methods:
- Synthesis of a series of retinoids with restricted conformations, including cyclic analogues.
- Assay 1: Reversal of keratinization in vitamin A-deficient hamster tracheal organ culture.
- Assay 2: Inhibition of mouse epidermal ornithine decarboxylase induction by a tumor promoter.
- In vivo testing for inhibition of papilloma tumor formation in mice.
- Toxicity assessment of active compounds.
Main Results:
- Several synthesized retinoids demonstrated activity comparable to retinoic acid in cell differentiation assays.
- Specific analogues, including 7, 13, 14, and 19, effectively inhibited papilloma tumor formation in mice.
- Compounds 13 and 14 exhibited lower toxicity than retinoic acid, while analogue 7 showed higher toxicity.
Conclusions:
- Conformationally restricted retinoids can effectively modulate cell differentiation and inhibit tumor development.
- Structural modifications significantly impact retinoid activity and toxicity.
- Compounds 13 and 14 represent promising candidates for further investigation due to their favorable efficacy and safety profiles.