1-[[[5-(substituted phenyl)-2-oxazolyl]methylene]amino]-2,4- imidazolidinediones, a new class of skeletal muscle relaxants.

A series of 1-[[[5-(substituted phenyl)-2-oxazolyl]methylene]amino]- 2,4-imidazolidinediones (6a-t) was synthesized, and the compounds were evaluated for direct skeletal muscle inhibition in the pithed rat gastrocnemius muscle preparation. The correctness of structural assignment of the new series was verified by alternate, unequivocal synthesis of one representative structure (6f). The phenyloxazoles 6d, 6g, 6j, 6k, and 6l exhibited significant skeletal muscle relaxant activity when administered intravenously and orally. The skeletal muscle relaxant effect of these five compounds is similar to that of other direct-acting skeletal muscle relaxants. The oxazole moiety proved to be an acceptable isosteric replacement for furan, as the biological activity in the oxazole series was retained. The synthesis of this new class of compounds is described, and pharmacologic evaluation data are presented. A discussion of structure-activity relationships is also presented.

5-phenyl-2-furamidines: a new chemical class of potential antidepressants.

A series of 5-phenyl-2-furamidines has been synthesized and evaluated for antidepressant activities. Substitution in the phenyl ring with a nitro (4) or an amino (12) group in the ortho-position resulted in an increase in antidepressant activity. Both 4 and 12 antagonized tetrabenazine-induced ptosis in rodents and inhibited norepinephrine (noradrenaline) uptake into crude synaptosomes of whole mouse brain at doses or concentrations comparable to those of the tricyclic antidepressants. However, these compounds did not possess the anticholinergic and antihistaminic activities common to tricyclic antidepressants. In addition, they lacked monoamine oxidase inhibitory activity. The 5-phenyl-2-furamidines represent a new chemical class of antidepressants and may be useful for depressive patients who cannot tolerate the compromising side effects of the tricyclic antidepressants and monoamine oxidase inhibitors.

Synthesis and skeletal muscle relaxant activity of 3-(aminoacyl)-1-[[[5-(substituted phenyl)-2-furanyl]methylene]amino] -2,4-imidazolidinediones.

A series of 3-(aminoacyl)-1-[[[5-(substituted phenyl)-2-furanyl] methylene]amino]-2,4-imidazolidinediones was synthesized and evaluated for skeletal muscle relaxant activity. All compounds were active by the intravenous route, and nine of 11 were active orally. One compound was very active when evaluated by the mouse Straub tail and rotarod tests; its efficacy index (ED50 rotarod/ED50 Straub tail) was 2.0, while its therapeutic index (LD50/ED50 Straub tail) was > 225.

1-(substituted benzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidones: a series with stimulant and depressant activities.

A series of 1-(substituted benzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidones was synthesized primarily by catalytic hydrogenation of the corresponding 1-(substituted benzyl)-2(1H)-pyrimidone. The pharmacological evaluation of these compounds in mice revealed a unique profile that included evidence of CNS stimulation and depression within the series and in the same compounds. Some members of this series induced signs of only CNS stimulation, some compounds caused signs of only CNS depression and skeletal muscle relaxation, and some caused signs of both stimulation and depression in the same animal. This apparent dual activity was assessed further in mice with antidepressant tests based on tetrabenazine antagonism and with antianxiety/anticonvulsant tests on the antagonism of a number of convulsants. The 4-chloro-, 4-fluoro-, 4-bromo-, and 3,4-dichlorobenzyl compounds exhibited antidepressant and antianxiety activities in the same dose range. Among these four compounds, the 3,4-dichlorobenzyl compound possessed the lowest antitetrabenazine (17 mg/kg po) and antipentylenetetrazol (23 mg/kg po) ED50 values. The 4-fluoro compound antagonized tetrabenazine-, pentylenetetrazol-, and isoniazid-induced tonic convulsions in the same dose range (congruent to 50 mg/kg po).

Pharmacology of 1-(3,4-dichlorobenzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidone, a novel antidepressant compound with antianxiety activity.

1-(3,4-dichlorobenzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidone (I) was evaluated in selected pharmacological tests, and its activity was compared to that of some clinically useful psychotropic drugs. Based on the results, it is evident that I has a unique profile of antidepressant and antianxiety activities that are evident in the same dose range. The mechanism of its antidepressant activity is proposed to be similar to the tricyclic antidepressants, that is, inhibition of norepinephrine uptake. Neither I nor the tricyclic antidepressants possess monoamine oxidase-inhibiting activity. However, unlike the tricyclic antidepressants, I is devoid of any significant anticholinergic activity and presumably is free of anticholinergic side effects.

Isolation, synthesis, and pharmacology of metabolites of 1-(3,4-dichlorobenzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidone.

The metabolism of 1-(3,4-dichlorobenzyl)-3,4,5,6-tetrahydro-2(1H)-pyrimidone, an antianxiety/antidepressant agent, in dogs is reported. Two metabolites, 3-[1-(3,4-dichlorobenzyl)-1-ureido]propanoic acid and 1-(3,4-dichlorobenzyl)uracil, were isolated, characterized, and synthesized. Neither metabolite was acutely toxic, and they did not exhibit antidepressant or antianxiety/anticonvulsant activity.

Synthesis and antidepressant activity of 5-(4-dimethylaminobenzyl)imidazolidine-2,4-dione.

5-(4-Dimethylaminobenzyl)imidazolidine-2,4-dione was prepared by catalytic hydrogenation of the corresponding benzylidene compound. Antidepressant testing in mice indicated that its ED50 values for antagonism of tetrabenazine-induced ptosis and potentiation of levodopa-induced behavioral changes were 42 and 17 mg/kg po, respectively. In vitro neurochemical studies demonstrated that this compound did not inhibit the uptake of selected biogenic amines into crude synaptosomes of mouse whole brain, and it did not have significant monoamine oxidase inhibitory activity in vivo and vitro. Thus, this compound possesses potential antidepressant activity with a mechanism different from that of the tricyclic antidepressants and monoamine oxidase inhibitors.

Synthesis and skeletal muscle relaxant activity of quaternary ammonium salts of dantrolene and clodanolene.

A series of quaternary ammonium salts of dantrolene and clodanolene was prepared and evaluated for skeletal muscle relaxant activity. The quaternary ammonium salts exhibit greater aqueous solubility and, therefore, facilitate intravenous administration. One member of this series, although less effective orally, exhibited greater aqueous solubility than the sodium salt. When administered intravenously, it was a more potent antagonist of skeletal muscle contraction and yielded comparable therapeutic and muscle relaxant efficacy indexes.

The pharmacology of clodanolene sodium, a new skeletal muscle contraction antagonist.

The pharmacology of hydrated 1 less than ([5-(3,4-dichlorophenyl)-2-furanyl]methylene) amino greater than-2,4,-imidazolidinedione sodium salt (clodanolene sodium), as skeletal-muscle contraction antagonist, is presented. Clodanolene sodium is remarkable in that it has no measurable direct effect on the peripheral or central nervous systmes. Skeletal muscle relaxation can be achieved with this drug at doses that do not affect motor coordination. Rats receiving clodanolene sodium for up to 30 days evidenced a downward trend in gross observation score of skeletal muscle relaxation, but the extent of twitch inhibition was the same on day 30 as on day 1. In an animal model of muscle spasticity (Straub-tail mouse), clodanolene sodium has been shown to be more efficacious for induction of skeletal muscle relaxation than neuromuscular blocking agents, local anesthetics, or centrally-acting muscle relaxants. Clodanolene sodium's mode of action has been identified as specific for skeletal muscle. It has no measurable effect on neuromuscular transmission or on the electrically excitable surface membrane. Indirect evidence indicates that the site of action of clodanolene sodium, like that of dantrolene sodium, is within the muscle cell and is related to caffeine-sensitive calcium stores. Its skeletal-muscle relaxant activity, we suggest results from a decrease in the release of calcium from the sarcoplasmic reticulum.

Synthesis and comparative skeletal muscle relaxant activity of some 2,4-imidazolidinediones and their corresponding 5-hydroxy-2,4-imidazolidinediones.

A series of 5-hydroxy substitution products of 2,4-imidazolidinediones, including the 5-hydroxy metabolite of the skeletal muscle contraction antagonist, dantrolene sodium, has been synthesized and evaluated for skeletal muscle relaxant activity. Most of these analogues are active in vivo with iv administration and in vitro. While two analogues are also active by oral and ip administration, only 1-[[[5-(3,4-dichlorophenyl)-2-furanyl]methylene]amino]-5-hydroxy-2,4-imidazolidinedione is sufficiently active in inhibiting the Straub tail in mice. However, none of these analogues has a muscle relaxant efficacy index greater than 1, comparable to dantrolene.

Muscle relaxant properties of the identified metabolites of dantrolene.

Identified metabolites of dantrolene, a skeletal muscle relaxant, were studied for inhibition of skeletal muscle contractions. Inhibition of muscle contractions were studied in vivo in the rat gastrocnemius muscle preparation, and in vitro using isolated rat diaphragm strips. Dantrolene (D) and 5-hydroxydantrolene (5-HD) inhibited muscle contraction responses in a dose dependent manner, both in vivo and in vitro. 5-HD was less potent than D.

A comparison of skeletal, cardiac, and smooth muscle actions of dantrolene sodium--a skeletal muscle relaxant.

Dantroline sodium, a skeletal muscle relaxant, has been proposed to inhibit the relase of Ca++ from the sarcoplasmic reticulum. Such a mechanism suggests that other muscle contractile systems operating with the same Ca++ denominator should also be affected by the drug. In the present studies dantrolene sodium effects on smooth, cardiac and skeletal muscle have been evaluated with in situ and in vitro techniques. In anesthetized dogs in situ skeletal muscle contractions were inhibitied in a dose-dependent manner, but cardiac muscle contractions were not. Effects on intestinal smooth muscle responses were highly variable and of short duration. In vitro, ED50 values were developed with dantrolene sodium (0.15-120 mg/l) in DMSO for each tissue. Skeletal muscle was the most sensitive (ED50 = 4.1 mg/l), cardiac muscle contractions were not inhibited by the drug and intestinal smooth muscle (ED50 = 59.0 mg/l) was approximately 1/14 as sensitive as skeletal muscle. It is concluded that skeletal muscle is uniquely sensitive to dantrolene sodium. A hypothesis for this specific action is offered.

Effects of intravenous dantrolene sodium on respiratory and cardiovascular functions.

Dantrolene sodium, a peripherally acting skeletal muscle relaxant, at doses up to 30 mg/kg iv had no effect on respiratory volume, respiratory rate, blood pressure, or heart rate in anesthetized dogs. The ED50 for inhibition of skeletal muscle contractions was 4.5 mg/kg in anesthetized dogs. In anesthetized sheep, the ED50 for skeletal muscle relaxation was 3.2 mg/kg under methoxyflurane anesthesia and 1.7 mg/kg under pentobarbital anesthesia. Unanesthetized sheep administered doses up to 30 mg/kg iv evidenced no dose-related cardiovascular effects. Respiratory volume decreased and respiratory rate increased, with the net result that the respiratory minute volume was not affected by dantrolene sodium. The results indicate that dantrolene sodium has no effect on the cardiovascular or respiratory systems that would preclude its use intravenously in acute conditions where direct relaxation of skeletal muscle is required, as in the management of malignant hyperthermia.