Linda A. Geelhaar

Pyrrolines as Prodrugs of γ-Aminobutyric Acid Analogues

Abstract: Δ′‐Pyrroline, S‐methyl‐Δ′‐pyrroline, and 5.5‐dimethyl‐Δ′‐pyrroline have been identified as substances metabolized to γ‐aminobutyric acid (GABA), 4‐aminopentanoic acid (raethyl GABA), and 4‐amino‐4‐methylpen‐tanoic acid (dimethyl GABA), respectively. An enzyme system residing in the soluble fraction of rabbit liver catalyzes the conversion of Δ′‐pyrroline to GABA and its lactam, 2‐pyrrolidinone. Acetaldehyde, allopurinol, and cyanide inhibited the reaction. Incubation of deuterium‐labeled Δ′‐pyrroline with mouse brain homogenates produced deuterated GABA. Mouse liver 10,000 g supernatant and mouse brain homogenates converted S‐methyl‐Δ′‐pyrroline to methyl GABA, and 5,5‐dimethyl‐Δ′‐pyrroline to dimethyl GABA. Four hours after intraperitoneal injection of 5‐methyl‐Δ′‐pyrroline (200 mg/kg), methyl GABA was detected in mouse brain (0.27 μ‐mol/g). Dimethyl GABA (1.21 μmol/g) was determined in mouse brain 30 min after intraperitoneal administration of 5.5‐dimethyl‐Δ′‐pyrroline (200 mg/kg). Neither methyl GABA nor dimethyl GABA penetrated into the central nervous system when administered in the periphery. The present studies suggest that pyrrolines may represent a chemical class of brain‐penetrating precursors of pharmacologically active analogues of GABA.

Biosynthesis of 5-Aminopentanoic Acid and 2-Piperidone from Cadaverine and 1-Piperideine in Mouse

1‐Piperideine, 5‐aminopentanoic acid, and its lactam, 2‐piperidone, were identified as metabolites of cadaverine in 10,000 g mouse liver supernatants to which diamine oxidase had been added. Both metabolites were also found when the cadaverine metabolite 1‐piperideine was incubated with the preparation which suggested that 1‐piperideine is an intermediate in the formation of 5‐ammopentanoic acid and 2‐piperidone. Identification of the metabolites was based on gas chromatography‐mass spectrometric analysis in comparison to authentic standards. Mouse brain homogenates converted 1‐piperideine to 5‐aminopentanoic acid. The results suggest that the metabolic fate of cadaverine may provide precursors of pharmacologically active analogues of GABA.

Biological denitration of propylene glycol dinitrate by Bacillus sp. ATCC 51912.

In previous studies, bacterial cultures were isolated that had the ability to degrade the nitrate ester glyceryl trinitrate (i.e. nitroglycerin). The goal of the present study was to examine the ability of resting cells and cell-free extracts of the isolateBacillus sp. ATCC 51912 to degrade the more recalcitrant nitrate ester propylene glycol dinitrate (PGDN). It was observed that the PGDN-denitrating activity was expressed during growth even when cells were cultured in the absence of nitrate esters. This indicates that nitrate esters are not required for expression of denitration activity. Using cell-free extracts, PGDN was observed to be sequentially denitrated to propylene glycol mononitrate (PGMN) and propylene glycol with the second denitration step proceeding more slowly than the first. Also it was observed that dialysis of the cell-free extracts did not affect denitration activity indicating that regenerable cofactors [e.g. NAD(P)H or ATP] are not required for denitration.

Isotopically sensitive regioselectivity in the oxidative deamination of a homologous series of diamines catalyzed by diamine oxidase

The equivalence of aminomethylene groups in selected diamine substrates of diamine oxidase was exploited for the determination of intramolecular isotope effects. In the series of substrates, [1,1-2H2]-1,3-diaminopropane, [1,1-2H2]-1,5-diaminopentane, [1,1-2H2]-1,6-diaminohexane, [1,1-2H2]-1,7-diaminoheptane and [alpha,alpha-2H2]-4-(aminomethyl)benzylamine, the preference of the enzyme for reaction at the unlabeled methylene was found to vary from 1.45 to 10.5-fold. The observed partitioning ratios go through a minimum value with 1,5-diaminopentane, the best substrate of diamine oxidase of the compounds tested. The results suggest that fast substrates have less opportunity to reorient into alternate binding conformations while bound to the active site of the enzyme. On the other hand, diamine substrates tested that cannot exist in energetically favorable conformations with internitrogen distances of about 7-8 A showed larger intramolecular isotope effects.

1‐Piperideine as an In Vivo Precursor of the γ‐Aminobutyric Acid Homologue 5‐Aminopentanoic Acid

Abstract: Intraperitoneal injection of the cyclic imine I‐piperideine in mice resulted in measurable quantities of 5‐aminopentanoic acid in brain. 5‐Aminopentanoic acid is a methylene homologue of γ‐aminobutyric acid (GABA) that is a weak GABA agonist. 5‐Aminopentanoic acid formed in the periphery was ruled out as the source of brain 5‐aminopentanoic acid based on the absence of detection in brain following injection of 100 mg/kg of 5‐aminopentanoic acid. Deuterium‐labeled I‐piperideine was prepared by exchange in deuterated phosphate buffer. Injection of [3,3‐2H2] 1‐piperideine yielded [2,2‐2H2]5‐aminopentanoic acid in brain. The results are consistent with uptake of 1‐piperideine into brain and oxidation of the precursor to 5‐aminopentanoic acid. Inhibition of GABA catabolism by pretreatment with aminooxyacetic acid increased brain concentrations of 5‐aminopentanoic acid formed from 1‐piperideine, suggesting that 5‐aminopentanoic acid is an in vivo substrate of 4‐aminobutyrate:2‐oxoglutarate aminotransferase.