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New analgesics synthetically derived from the paracetamol metabolite N-(4-hydroxyphenyl)-(5Z,8Z,11Z,14Z)-icosatetra-5,8,11,14-enamide.

Journal of medicinal chemistry (2008-12-05)
Christian Sinning, Bernhard Watzer, Ovidiu Coste, Rolf M Nüsing, Ingo Ott, Alessia Ligresti, Vincenzo Di Marzo, Peter Imming
ABSTRACT

N-(4-hydroxyphenyl)-(5Z,8Z,11Z,14Z)-icosatetra-5,8,11,14-enamide (AM404) is a metabolite of the well-known analgesic paracetamol. AM404 inhibits endocannabinoid cellular uptake, binds weakly to CB1 and CB2 cannabinoid receptors, and is formed by fatty acid amide hydrolase (FAAH) in vivo. We prepared three derivatives of this new (endo)cannabinoid using bioisosteric replacement (1), homology (2), and derivatization (3) of the 4-aminophenol moiety in AM404 and tested them against CB1, CB2, and FAAH. We found affinities toward both cannabinoid receptors equal to or greater than that of AM404. Shortening the acyl chain from C20 to C2 led to three new paracetamol analogues: N-(1H-indazol-5-yl)acetamide (5), N-(4-hydroxybenzyl)acetamide (6), and N-(4-hydroxy-3-methoxyphenyl)acetamide (7). Again, 5, 6, and 7 were tested against CB1, CB2, and FAAH without significant activity. However, 5 and 7 behaved like inhibitors of cyclooxygenases in whole blood assays. Finally, 5 (50 mg/kg) and 6 (275 mg/kg) displayed analgesic activities comparable to paracetamol (200 mg/kg) in the mouse formalin test.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Acetaminophen, analytical standard
Sigma-Aldrich
Acetaminophen, BioXtra, ≥99.0%
Sigma-Aldrich
Acetaminophen, meets USP testing specifications, 98.0-102.0%, powder
Sigma-Aldrich
Ketoprofen, ≥98% (TLC)
Sigma-Aldrich
Ketoprofen, meets USP testing specifications