Warfarin derivatives

The preparation of warfarin derivatives via the catalysed Michael-type reaction of 4-hydroxycoumarins with 4-arylbut-3-en-2-ones is achieved with a ca. 20-fold increase in reaction rate and a twofold increase in yields, compared with traditional methods [60]. Similarly, tetra-H-butylammonium fluoride catalyses the reaction of nitrotoluenes with a,p-unsaturated esters under mild soliddiquid two-phase conditions [14] with increased yields, compared with those observed in the absence of the catalyst. 

Scheme 16 3-Alkylated 4-hydroxycoumarins the core structure for various warfarin derivatives...

Scheme 19 Bi(OTf)3-catalyzed synthesis of novel warfarin derivatives...

In addition, this method has been extended to 4-hydroxycoumarin nucleophiles. This method represents a highly efficient synthetic route to new warfarin derivatives (Scheme 33). Again, 5 mol% of the Lewis acid was necessary to obtain the desired... 

Scheme 33 Hydroalkylation of 4-hydroxycomarin yields highly desirable warfarin derivatives...

Tummino PJ, Fergusson D. Hupe D. Competitive inhibition of HIV-1 protease by warfarin derivatives. Biochem. Biophys. Res. Commun. 1994 201 290-294. 

I6I C. Warfarin baits need contain only 0 025% active principle, and rats are killed after ingesting about 5 doses the bait can be left down and the risk of acute toxicity to man or domestic animals is not serious. In common with other coumarin derivatives, warfarin reduces the clotting power of blood and death is caused by haemorrhages initiated by any slight injury. Warfarin is a vitamin K antagonist, and large oral doses of the vitamin can be given as an antidote. 

Hydroxycoumarin [1076-38-6] can be synthesized by cyclization of acetyl methyl salicylate. It is a coumatin metaboHte occurring in spoiled hay. Derivatives of 4-hydroxycoumarin such as dicoumarol [66-76-2] warfarin [81-81-2] cyclocoumarol [518-20-7] ethylbis—coumaracetate [548-00-5] and bis-4-hydroxycoumarin [25892-93-7] are synthetic blood anticoagulants (see Blood, coagulants and anticoagulants). 

The isoprene-derived molecule whose structure is shown here is known alternately as Coumarin and warfarin. By the former name, it is a widely prescribed anticoagulant. By the latter name, it is a component of rodent poisons. How can the same chemical species be used for such disparate purposes The key to both uses lies in its ability to act as an antagonist of vitamin K in the body. 

Further work in this area showed that only one of the cou-marin rings was needed for biologic activity. Condensation of the hydroxyacetophenone, 4, with diethyl carbonate affords 4-hydroxycoumarin (2). The reaction may involve the 3-ketoester (5) cyclization of this would afford 2. Alternately, the reagent may first give the 0-acyl derivative cyclization as above will give the same product. Michael condensation of the coumarin with benzalacetone (6) affords the anticoagulant warfarin (named after its place of origin Wisconsin Alumni Research Foundation,... 

Matricaria recutita, known as German chamomile, is also purported to have antispasmodic properties. It is taken most often as a tea up to four times a day. Benzodiazepine, alcohol, and warfarin users should be cautioned against taking this product because it can cause drowsiness, and it contains coumarin derivatives.20... 

The enantioselective reduction of unsaturated alcohol derivatives has been applied to the synthesis of several biologically active compounds (Scheme 24.12). Warfarin (123, R=H) is an important anticoagulant that is normally prescribed as the racemate, despite the enantiomers having dissimilar pharmacological profiles. One of the earliest reported uses of DuPhos was in the development of a chiral switch for this bioactive molecule, facilitating the preparation of (R)- and (S)-warfarin [184]. Although attempted reduction of the parent hydroxycoumarin 122 (R=H) led to formation of an unreactive cyclic hemiketal, hydrogenation of the sodium salt proceeded smoothly with Rh-Et-DuPhos in 86-89% ee. 

More recent developments in the field of the Pirkle-type CSPs are the mixed r-donor/ r-acceptor phases such as the Whelk-Of and the Whelk-02 phases.The Whelk-Of is useful for the separation of underiva-tized enantiomers from a number of families, including amides, epoxides, esters, ureas, carbamates, ethers, aziridines, phosphonates, aldehydes, ketones, carboxylic acids, alcohols and non-steroidal anti-inflammatory drugs.It has been used for the separation of warfarin, aryl-amides,aryl-epoxides and aryl-sulphoxides. The phase has broader applicability than the original Pirkle phases. The broad versatility observed on this phase compares with the polysaccharide-derived CSPs... 

Fig. 14.8 Experimental ligand interactions with cytochrome P450 2C family. (A) X-ray structure ofthe sulfaphenazole derivate DMZ in rabbit CYP2C5 at 2.3 A resolution (PDB 1 N5B) from Wester et al. [191]. Only one ofthe two-ligand orientations for DMZ in accord with electron density is shown placing the benzylic methyl group in a 4.4 A distance to the heme iron. (B) X-ray structure of S-warfarin in human CYP2C9 at 2.55 A resolution (PDB 10G5) from Williams et al. [192]. The substrate is situated in a predominantly hydrophobic pocket. This binding mode places the 6- and 7-hydroxylation sites 10 A from the iron (arrow).

Because rodent populations world-wide were becoming resistant to the widely used Warfarin-type anticoagulant poisons, a search was initiated to find a rodenticide with a different mode of action one that would be effective against these resistant rodents. This search led to the discovery of the toxic nature of a family of diphenyl amines which act as uncouplers of oxidative phosphorylation. A structure-activity relationship (SAR) study was undertaken to choose a derivative that would be both poisonous to rodents but still readily consumed by them. This approach led to the discovery of bromethalin,... 

Anticoagulants used therapeutically include heparin, warfarin (a coumarin derivative), and anisindione (an indandione derivative). 

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