Cimetidine and ranitidine: their interaction with human and pig liver microsomes and with purified cytochrome P-450.

Cimetidine and ranitidine interact with microsomes from human and pig liver and with purified cytochrome P-450 in the ligand-type manner. The affinity for cimetidine is about 10 times as high as that for ranitidine. Accordingly amplitudes of the specta are much higher for cimetidine. These results are in accordance with those obtained earlier with rat liver microsomes. The inhibitory potency of either compound with regard to dealkylation of 7-ethoxycoumarin appears to be less in the human preparation.

Characterization of cimetidine, ranitidine, and related structures' interaction with cytochrome P-450.

Cimetidine (I) interacts with the hemin iron of cytochrome P-450 from rat liver microsomes, with its imidazole and cyano coordinating groups. Ranitidine (II) interacts through its nitronic acid oxygen and its amine nitrogen, as shown by optical difference and ESR-spectra. I, N-cyano-N'[2-[[[5-(dimethylamino)-methyl-2-furanyl]methyl] thio]-ethyl]-N"-methyl guanidine (IV), 4(5)-hydroxymethyl-5(4)-methyl imidazole (VII), 4(5)-methyl-5(4)-[(2-aminoethyl)-thiomethyl]-imidazole hydrochloride (IX), 2-[[[(5-dimethylamino)-methyl-2-furanyl]-methyl]-thio]ethene amine dihydrochloride (X) and imidazole (XI) inhibit 7-ethoxycoumarin dealkylation competitively. In I both imidazole and cyano groups contribute to the inhibitory activity, the latter group being more effective according to electron spin resonance. Mixed type inhibition was observed with II, desmethylranitidine (VIII) and N-[[2-(5-methylimidazol-4-yl)methylthio]-ethyl]-N'-methyl-2-nitro-1, 1-ethenediamine (III). These compounds inhibited the reaction to a small extent; ranitidine S-oxide (VI) did not interact at all with microsomes from phenobarbital-pretreated rats. Using microsomes from 3-methylcholanthrene-pretreated rats, the affinities of interaction and the amplitudes of optical difference spectra were higher with VIII than with its parent, compound II.

Interaction of ranitidine with liver microsomes.

1. Ranitidine interacts with liver microsomes from rats pretreated with different inducers of cytochrome P-450 to produce substrate difference optical spectra with a peak at 426-429 nm and a trough at 390-400 nm. 2. Cytochrome P-450 reduced with dithionite in the presence of ranitidine produced substrate difference spectra with a peak at 447 nm. 3. Ks values for the interaction of ranitidine with cytochrome P-450 (not reduced), calculated from double reciprocal plots, were in the range 1.4-2.8 mM. 4. The O-dealkylation of 7-ethoxycoumarin and of p-nitroanisole was inhibited by the presence of ranitidine and the inhibition was of a mixed type. Kii and Kis values were: for inhibition of 7-ethoxycoumarin dealkylation, 0.8 to 9 mM, and 0.16 to 0.67 mM, respectively; for inhibition of p-nitroanisole dealkylation, 5.8 to 13.7 mM, and 1 to 4.5 mM, respectively. 5. The I50 values for 7-ethoxycoumarin dealkylation was 1.8 mM and for p-nitroanisole dealkylation about 7.2 mM (microsomes from phenobarbital-pretreated rats). 6. The e.p.r. spectra of cytochrome P-450 from phenobarbital-pretreated rats, in the presence of ranitidine, reveal two types of interaction depending on the ranitidine concentration. At lower concentrations of ranitidine, a ligand exchange reaction with an oxygen atom is indicated, and at higher concentrations are with nitrogenous or thioether ligand of ranitidine.

Stereochemical characterization of interactions of chiral 1,4-benzodiazepine-2-ones with liver microsomes.

Microsomal P-450 cytochrome are stereoselective toward 7-Chloro-1,3-dihydro-3(S)-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one. (S)-1, and 7-chloro-1,3-dihydro-3(S)-isopropyl-5-phenyl-2H-1,4-benzodiazepin-2-one, (S)-2. (S)-enantiomers bind to a substrate binding site which accomodates the stable M-conformation (Ks =0.01 to 0.018 mmol/l). (R)-enantiomers, however, undergo a ligand type of interaction (Ks = 0.036 to 0.12 mmol/l). Prochiral desmethyldiazepam behaves similarly to the (S)-enantiomers of the above compounds. The ligand binding site does not differentiate between M- and P-conformers.

Synthesis of some carbon-3 substituted 1,4-benzodiazepin-2-ones and their central nervous system effects.

Starting from 3-hydroxy-1,4-benzodiazepin-2-ones 1--3, via 3-chloro derivatives 4--6, 13 new C(3)-substituted 1,4-benzodiazepin-2-ones were synthesized. Reaction of 4--6 with ethylene glycol yielded 3-(beta-hydroxyethyl) derivatives 7--9. Similar reaction with the isopropylidene derivative of glycerol afforded 10--12, which on hydrolysis of the isopropylidene group hielded glycerol derivatives 13--15. Reaction of trichloroacetyl chloride with oxazepam and temazepam yielded the corresponding trichloroacetyl esters 16 and 17. The beta-hydroxyethyl derivative 7 was conjugated with an acetylated glucopyranose derivative to give isomeric 18 and 19. Partition coefficients (log Poct) and central nervous system activities (in six stranded tests) were determined for 7--15 as well as several standard compounds. Most of the compounds exhibiting beneficial central nervous system activity had Poct values between 1.71 and 2.48. No correlation between lipophilicity and central nervous system activity could be discerned for these compounds.

Study of the sporulation of Bacillus thuringiensis var. thuringiensis.

During the submerged cultivation of Bacillus thuringiensis var. thuringiensis in 300- and 3000-liter fermentors, lysis occurred at the end of the exponential phase of growth. New vegetative cells were subsequently formed which usually sporulated. At time of lysis, the amount of soluble sugar was 1-12 g/liter, pH value dropped to 5.3-5.8 from the original PH 6.8 and started to rise after all the cells had lysed. The proteolytic activity was low during the lysis and increased as the sporulation commenced.

Chiral 1,4-benzodiazepine. VII. Cyclization rates of 2-(n-alpha-ammoniumacyl)-amino-5-chloro-benzophenones in the chiral 1,4-benzodiazepin-2-ones.

Cyclisation rates of some S-alpha-amino acid derivatives (I--VII) into chiral 1,4-benzodiazepin-2-ones were determined under physiological-like conditions (pH, temperature) and plotted against pKa values of the corresponding alpha-amino acids. No correlation between k, i.e. t1/2 values, of the acidic precursors, and pharmacodynamic activity, as determined by some standard tests, were observed, however. Unambiguity of cyclisation, and its t1/2 values reveal benefit for physico-chemical properties of the investigated acyclic precursors as transport-forms of the chiral 1,4-benzodiazepin-2-ones with prolonged pharmacological activity.