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All-trans-retinoic acid (atRA), the active metabolite of vitamin A, induces gene transcription via binding to nuclear retinoic acid receptors (RARs). The primary hydroxylated metabolites formed from atRA by CYP26A1, and the subsequent metabolite 4-oxo-atRA, bind to RARs and potentially have biologic activity. Hence, CYP26A1, the main atRA hydroxylase, may function either to deplete bioactive retinoids or to form active metabolites. This study aimed to determine the role of CYP26A1 in modulating RAR activation via formation and elimination of active retinoids. After treatment of HepG2 cells with atRA, (4S)-OH-atRA, (4R)-OH-atRA, 4-oxo-atRA, and 18-OH-atRA, mRNAs of CYP26A1 and RARβwere increased 300- to 3000-fold, with 4-oxo-atRA and atRA being the most potent inducers. However, >60% of the 4-OH-atRA enantiomers were converted to 4-oxo-atRA in the first 12 hours of treatment, suggesting that the activity of the 4-OH-atRA was due to 4-oxo-atRA. In human hepatocytes, atRA, 4-OH-atRA, and 4-oxo-atRA induced CYP26A1 and 4-oxo-atRA formation was observed from 4-OH-atRA. In HepG2 cells, 4-oxo-atRA formation was observed even in the absence of CYP26A1 activity and this formation was not inhibited by ketoconazole. In human liver microsomes, 4-oxo-atRA formation was supported by NAD+, suggesting that 4-oxo-atRA formation is mediated by a microsomal alcohol dehydrogenase. Although 4-oxo-atRA was not formed by CYP26A1, it was depleted by CYP26A1 (Km= 63 nM and intrinsic clearance = 90 μl/min per pmol). Similarly, CYP26A1 depleted 18-OH-atRA and the 4-OH-atRA enantiomers. These data support the role of CYP26A1 to clear bioactive retinoids, and suggest that the enzyme forming active 4-oxo-atRA may be important in modulating retinoid action.

Recent guidance on drug-drug interaction (DDI) testing recommends evaluation of circulating metabolites. However, there is little consensus on how to quantitatively predict and/or assess the risk of in vivo DDIs by multiple time-dependent inhibitors (TDIs) including metabolites from in vitro data. Fluoxetine was chosen as the model drug to evaluate the role of TDI metabolites in DDI prediction because it is a TDI of both CYP3A4 and CYP2C19 with a circulating N-dealkylated inhibitory metabolite, norfluoxetine. In pooled human liver microsomes, both enantiomers of fluoxetine and norfluoxetine were TDIs of CYP2C19, (S)-norfluoxetine was the most potent inhibitor with time-dependent inhibition affinity constant (KI) of 7 μM, and apparent maximum time-dependent inhibition rate (kinact,app) of 0.059 min−1. Only (S)-fluoxetine and (R)-norfluoxetine were TDIs of CYP3A4, with (R)-norfluoxetine being the most potent (KI= 8 μM, and kinact,app= 0.011 min−1). Based on in-vitro-to-in-vivo predictions, (S)-norfluoxetine plays the most important role in in vivo CYP2C19 DDIs, whereas (R)-norfluoxetine is most important in CYP3A4 DDIs. Comparison of two multiple TDI prediction models demonstrated significant differences between them in in-vitro-to-in-vitro predictions but not in in-vitro-to-in-vivo predictions. Inclusion of all four inhibitors predicted an in vivo decrease in CYP2C19 (95%) and CYP3A4 (60–62%) activity. The results of this study suggest that adequate worst-case risk assessment for in vivo DDIs by multiple TDI systems can be achieved by incorporating time-dependent inhibition by both parent and metabolite via simple addition of the in vivo time-dependent inhibition rate/cytochrome P450 degradation rate constant (λ/kdeg) values, but quantitative DDI predictions will require a more thorough understanding of TDI mechanisms.

Itraconazole (ITZ) is a mixture of four cis-stereoisomers that inhibit CYP3A4 potently and coordinate CYP3A4 heme via the triazole nitrogen. However, (2R,4S,2'R)-ITZ and (2R,4S,2'S)-ITZ also undergo stereoselective sequential metabolism by CYP3A4 at a site distant from the triazole ring to 3'-OH-ITZ, keto-ITZ, and N-desalkyl-ITZ. This stereoselective metabolism demonstrates specific interactions of ITZ within the CYP3A4 active site. To further investigate this process, the binding and metabolism of the four trans-ITZ stereoisomers by CYP3A4 were characterized. All four trans-ITZ stereoisomers were tight binding inhibitors of CYP3A4-mediated midazolam hydroxylation (IC5016–26 nM), and each gave a type II spectrum upon binding to CYP3A4. However, instead of formation of 3'-OH-ITZ, they were oxidized at the dioxolane ring, leading to ring scission and formation of two new metabolites of ITZ. These two metabolites were also formed from the four cis-ITZ stereoisomers, although not as efficiently. The catalytic rates of dioxolane ring scission were similar to the dissociation rates of ITZ stereoisomers from CYP3A4, suggesting that the heme iron is reduced while the triazole moiety coordinates to it and no dissociation of ITZ is necessary before catalysis. The triazole containing metabolite [1-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-yl)ethanone] also inhibited CYP3A4 (IC50>15 μM) and showed type II binding with CYP3A4. The dioxolane ring scission appears to be clinically relevant because this metabolite was detected in urine samples from subjects that had been administered the mixture of cis-ITZ isomers. These data suggest that the dioxolane ring scission is a metabolic pathway for drugs that contain this moiety.

All-trans-retinoic acid (atRA) is the active metabolite of vitamin A. atRA is also used as a drug, and synthetic atRA analogs and inhibitors of retinoic acid (RA) metabolism have been developed. The hepatic clearance of atRA is mediated primarily by CYP26A1, but design of CYP26A1 inhibitors is hindered by lack of information on CYP26A1 structure and structure-activity relationships of its ligands. The aim of this study was to identify the primary metabolites of atRA formed by CYP26A1 and to characterize the ligand selectivity and ligand interactions of CYP26A1. On the basis of high-resolution tandem mass spectrometry data, four metabolites formed from atRA by CYP26A1 were identified as 4-OH-RA, 4-oxo-RA, 16-OH-RA and 18-OH-RA. 9-cis-RA and 13-cis-RA were also substrates of CYP26A1. Forty-two compounds with diverse structural properties were tested for CYP26A1 inhibition using 9-cis-RA as a probe, and IC50values for 10 inhibitors were determined. The imidazole- and triazole-containing inhibitors [S-(R*,R*)]-N-[4-[2-(dimethylamino)-1-(1H-imidazole-1-yl)propyl]-phenyl]2-benzothiazolamine (R116010) and (R)-N-[4-[2-ethyl-1-(1H-1,2,4-triazol-1-yl)butyl]phenyl]-2-benzothiazolamine (R115866) were the most potent inhibitors of CYP26A1 with IC50values of 4.3 and 5.1 nM, respectively. Liarozole and ketoconazole were significantly less potent with IC50values of 2100 and 550 nM, respectively. The retinoic acid receptor (RAR) γ agonist CD1530 was as potent an inhibitor of CYP26A1 as ketoconazole with an IC50of 530 nM, whereas the RARα and RARβ agonists tested did not significantly inhibit CYP26A1. The pan-RAR agonist 4-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid and the peroxisome proliferator-activated receptor ligands rosiglitazone and pioglitazone inhibited CYP26A1 with IC50values of 3.7, 4.2, and 8.6 µM, respectively. These data demonstrate that CYP26A1 has high ligand selectivity but accepts structurally related nuclear receptor agonists as inhibitors.

Three secondary amines desipramine (DES), (S)-fluoxetine [(S)-FLX], and N-desmethyldiltiazem (MA) undergo N-hydroxylation to the corresponding secondary hydroxylamines [N-hydroxydesipramine, (S)-N-hydroxyfluoxetine, and N-hydroxy-N-desmethyldiltiazem] by cytochromes P450 2C11, 2C19, and 3A4, respectively. The expected primary amine products, N-desmethyldesipramine, (S)-norfluoxetine, and N,N-didesmethyldiltiazem, are also observed. The formation of metabolic-intermediate (MI) complexes from these substrates and metabolites was examined. In each example, the initial rates of MI complex accumulation followed the order secondary hydroxylamine > secondary amine >> primary amine, suggesting that the primary amine metabolites do not contribute to formation of MI complexes from these secondary amines. Furthermore, the primary amine metabolites, which accumulate in incubations of the secondary amines, inhibit MI complex formation. Mass balance studies provided estimates of the product ratios of N-dealkylation to N-hydroxylation. The ratios were 2.9 (DES-CYP2C11), 3.6 [(S)-FLX-CYP2C19], and 0.8 (MA-CYP3A4), indicating that secondary hydroxylamines are significant metabolites of the P450-mediated metabolism of secondary alkyl amines. Parallel studies with N-methyl-d3-desipramine and CYP2C11 demonstrated significant isotopically sensitive switching from N-demethylation to N-hydroxylation. These findings demonstrate that the major pathway to MI complex formation from these secondary amines arises from N-hydroxylation rather than N-dealkylation and that the primary amines are significant competitive inhibitors of MI complex formation.

Itraconazole (ITZ) has three chiral centers and is administered clinically as a mixture of four stereoisomers. This study evaluated stereoselectivity in ITZ metabolism. In vitro experiments were carried out using heterologously expressed CYP3A4. Only (2R,4S,2'R)-ITZ and (2R,4S,2'S)-ITZ were metabolized by CYP3A4 to hydroxy-ITZ, keto-ITZ, and N-desalkyl-ITZ. When (2S,4R,2'R)-ITZ or (2S,4R,2'S)-ITZ was incubated with CYP3A4, neither metabolites nor substrate depletion were detected. Despite these differences in metabolism, all four ITZ stereoisomers induced a type II binding spectrum with CYP3A4, characteristic of coordination of the triazole nitrogen to the heme iron (Ks 2.2–10.6 nM). All four stereoisomers of ITZ inhibited the CYP3A4-catalyzed hydroxylation of midazolam with high affinity (IC50 3.7–14.8 nM). Stereochemical aspects of ITZ pharmacokinetics were evaluated in six healthy volunteers after single and multiple oral doses. In vivo, after a single dose, ITZ disposition was stereoselective, with a 3-fold difference in Cmax and a 9-fold difference in Cmin between the (2R,4S)-ITZ and the (2S,4R)-ITZ pairs of diastereomers, with the latter reaching higher concentrations. Secondary and tertiary ITZ metabolites (keto-ITZ and N-desalkyl-ITZ) detected in plasma were of the (2R,4S) stereochemistry. After multiple doses of ITZ, the difference in Cmax and Cmin decreased to 1.5- and 3.8-fold, respectively. The initial difference between the stereoisomeric pairs was most likely due to stereoselective metabolism by CYP3A4, including stereoselective first-pass metabolism as well as stereoselective elimination. However, stereoselective elimination was diminished after multiple dosing, presumably as a result of CYP3A4 autoinhibition. In conclusion, the metabolism of ITZ is highly stereoselective in vitro and in vivo.

The decline in bone mineral density that occurs after long-term treatment with some antiepileptic drugs is thought to be mediated by increased vitamin D3 metabolism. In this study, we show that the inducible enzyme CYP3A4 is a major source of oxidative metabolism of 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] in human liver and small intestine and could contribute to this adverse effect. Heterologously-expressed CYP3A4 catalyzed the 23- and 24-hydroxylation of 1,25(OH)2D3. No human microsomal cytochrome P450 enzyme tested, other than CYP3A5, supported these reactions. CYP3A4 exhibited opposite product stereochemical preference compared with that of CYP24A1, a known 1,25(OH)2D3 hydroxylase. The three major metabolites generated by CYP3A4 were 1,23R,25(OH)3D3, 1,24S,25(OH)3D3, and 1,23S,25(OH)3D3. Although the metabolic clearance of CYP3A4 was less than that of CYP24A1, comparison of metabolite profiles and experiments using CYP3A-specific inhibitors indicated that CYP3A4 was the dominant source of 1,25(OH)2D3 23- and 24-hydroxylase activity in both human small intestine and liver. Consistent with this observation, analysis of mRNA isolated from human intestine and liver (including samples from donors treated with phenytoin) revealed a general absence of CYP24A1 mRNA. In addition, expression of CYP3A4 mRNA in a panel of duodenal samples was significantly correlated with the mRNA level of a known vitamin D receptor gene target, calbindin-D9K. These and other data suggest that induction of CYP3A4-dependent 1,25(OH)2D3 metabolism by antiepileptic drugs and other PXR ligands may diminish intestinal effects of the hormone and contribute to osteomalacia.

Propranolol, deuterium‐ and 18O‐labeled propranolol and related compounds were analyzed using an ion trap mass spectrometer equipped with a modified Finnigan API electrospray interface. Sequential product ion (MSn) experiments were used to elucidate fragmentation pathways for these compounds. The observed ions were compared to those observed under electron impact (EI) conditions. The electrospray ionization (ESI) ion trap spectra, as well as the EI spectra, afford useful information to allow assignments of most product ions, many of which retain portions of the aliphatic three‐carbon side chain. Copyright © 1999 John Wiley & Sons, Ltd.

Propranolol, deuterium- and ¹⁸O-labeled propranolol and related compounds were analyzed using an ion trap mass spectrometer equipped with a modified Finnigan API electrospray interface. Sequential product ion (MS ⁿ ) experiments were used to elucidate fragmentation pathways for these compounds. The observed ions were compared to those observed under electron impact (EI) conditions. The electrospray ionization (ESI) ion trap spectra, as well as the EI spectra, afford useful information to allow assignments of most product ions, many of which retain portions of the aliphatic three-carbon side chain. Copyright © 1999 John Wiley & Sons, Ltd.

Propranolol, its 1"-mono-, di-, and trifluorinated analogs, and other related compounds were analyzed under electrospray ionization ion trap collision-induced dissociation (ESI-CID) and electron impact (EI) conditions. Interesting trends were observed in the fragment ions formed in both cases. Under ESI conditions, the abundances of product ions easily explained by protonation on the amine nitrogen decreased relative to the abundances of those formed from the ether-protonated species as the number of fluorines increased from zero to three. Under EI conditions, the distribution of fragment ions was shifted away from those arising from a nitrogen-centered cation radical and toward those arising from an ether oxygen-centered cation radical. The changes observed in apparent molecular sites of protonation and of ion radical formation in the mass spectra are consistent with the electron-withdrawing effects of the sequentially added fluorines. These effects are correlated with changes in solution phase pK a's of the fluorinated amines. Copyright © 1999 John Wiley & Sons, Ltd.

Propranolol, its 1″‐mono‐, di‐, and trifluorinated analogs, and other related compounds were analyzed under electrospray ionization ion trap collision‐induced dissociation (ESI‐CID) and electron impact (EI) conditions. Interesting trends were observed in the fragment ions formed in both cases. Under ESI conditions, the abundances of product ions easily explained by protonation on the amine nitrogen decreased relative to the abundances of those formed from the ether‐protonated species as the number of fluorines increased from zero to three. Under EI conditions, the distribution of fragment ions was shifted away from those arising from a nitrogen‐centered cation radical and toward those arising from an ether oxygen‐centered cation radical. The changes observed in apparent molecular sites of protonation and of ion radical formation in the mass spectra are consistent with the electron‐withdrawing effects of the sequentially added fluorines. These effects are correlated with changes in solution phase pKa's of the fluorinated amines. Copyright © 1999 John Wiley & Sons, Ltd.

Oxprenolol (1), like related β-adrenergic antagonists, undergoes oxidative N-dealkylation to form the corresponding 3-aryloxypropane-1,2-diol (2), 3-aryloxylactic acid (3), and 2-aryloxyacetic acid (4) metabolites. Compounds 3and 4were synthesized by conversion of 2-allyloxyphenol (5) to the aryloxyacetaldehyde 6and subsequent elaboration to the desired acids. Both acids (3and 4) and glycol 2were confirmed as metabolites formed from 1in vivo in the rat and in vitro in the rat liver 9000 ×gsupernatant fraction. Incubation of a pseudoracemate of 1, made up of equal molar amounts of (2S)-1-doand (2R)-1-d2, showed that 2and 3arise principally from (2S)-1by S/Rratios of ~ 5:1 and 2:1, respectively. On the other hand, acetic acid derivative 4arises about equally from both enantiomers of 1.

Abstract. The pharmacokinetics and the endocrine profile of a new low molecular somatostatin derivative, SMS 201–995, were investigated in a group of 35 normal subjects. Clearance studies (n = 6) for this peptide showed a prolonged half-life in plasma, 113 min, following single scinjections of 50 or 100 μg. Arginine stimulation tests (n = 6) were conducted immediately and 180 min after scinjection of 50 μg of SMS 201–995. The stimulatory effect of arginine on GH and insulin was counteracted by the peptide at the P< 0.001 and P< 0.02 significance level, respectively. Delayed arginine stimulation revealed a persistent blockade of the GH release (P< 0.02), whereas a recovery of the insulin response was observed. Plasma glucagon increments following a standard protein meal (n = 10) were significantly (P< 0.001) inhibited by previous scinjection of 50 μg of SMS 202–995. Pretreatment with 50 and 100 μ of SMS 202–995 sc(n = 9) inhibited (P< 0.001) the stimulatory effect of TRH (200 μg iv) on TSH without modifying basal levels. The injection of 100 μg/h during sleep completely abolished the nocturnal GH peak in 4 volunteers. No rebound rise after decline of the suppressive action on GH was recorded in any of the trials.Safety chemistries and blood coagulation studies remained normal and no side-effects or untoward reactions were recorded throughout the investigation.With its high potency, slow plasma clearance, and long action SMS 201–995 may represent a valuable tool in the long-term management of states of inappropriate GH secretion.

Cyanide anion was used to attempt to trap possible imine intermediates in the oxidative N-dealkylation of propranolol (1). Reaction of 3-(1-naphthoxy)-1-amino-2-propanol (desisopropylpropranolol, 2) with acetone provided this expected intermediate in an ∼7:1 ratio of oxazolidine 6to imine 5, as determined by 1H NMR. The mixture when treated with sodium cyanide gave the expected α-aminonitrile 7. Microsomal oxidation of propranolol in the presence of sodium cyanide gave two cyanide-containing adducts as shown by GC-MS (12aand 12b). Using specifically deuterated propranolols (8, 9, 10, and 11) as substrates showed both of these cyanide-containing adducts to have lost the N-isopropyl group. Compounds 12aand 12bwere shown to be diastereomeric αaL-aminonitriles arising from the reaction of 2with propionaldehyde, a contaminant from the ether used for extraction, and cyanide anion. Authentic 7, stable to derivatization and GC-MS conditions, rapidly decomposed under the conditions of the metabolic experiments.

The disposition of d-, l-, and d,l-disopyramide was studied in 5 conscious dogs after intravenous administration (15 mg/kg) of each compound using a balanced crossover design. The clearance of d-disopyramide (15.4 ± 5.10 ml/min/kg) was significantly greater than that of the l-isomer (9.45 ± 2.52 ml/min/kg) (p< 0.001). The clearance of the d,l,-mixture was intermediate between that obtained for the d-and l-isomers. The steady-state volume of distribution of the three compounds was similar (approximately 1.4 liters/kg). The elimination half-life reflected differences in clearance, being 76.4 ± 7.30 min for d-disopyramide, 112 ± 23.4 min for l-disopyramide, and 97.2 ± 15.1 min for d,l-disopyramide. The effect of general anesthesia with urethane and chloralose on the disposition of the compounds was also examined. General anesthesia decreased the clearance and increased the half-life of all three compounds. No consistent differences in the volume of distribution were observed with anesthesia as compared to control. Thus, there is stereoselective elimination of the optical isomers of disopyramide in the dog, and general anesthesia decreases the clearance of d-, l-, and d,l-disopyramide.

The pharmacokinetics and pharmacodynamics of d- and dl-verapamil were studied in conscious rabbits in randomized cross-over fashion. Following a single intravenous dose, there was a biexponential decline in plasma concentration with time. No differences were observed in the pharmacokinetic properties of the compounds. The mean (±SD) clearances of d- and dl-verapamil were 0.13 ± 0.03 and 0.12 ± 0.05 L/min/kg, respectively. The mean (±SD) steady-state volume of distribution was 9.7 ± 5.2 L/kg for d-verapamil and 8.1 ± 4.1 L/kg for dl-verapamil. No difference was observed between the compounds in their binding to plasma proteins. The mean (±SD) half-life in plasma was 98.7 ± 63.8 min for d-verapamil and 96.3 ± 38.0 min for dl-verapamil. In contrast to the lack of stereoselective differences in the pharmacokinetic properties of verapamil, there were marked differences in the pharmacodynamics of d- and dl-verapamil. dl-Verapamil appeared to prolong the PR interval to a greater degree than did d-verapamil, consistent with the more potent calcium channel effects of the l-enantiomer. Similarly, dl-verapamil had more potent hypotensive effects compared with the d-enantiomer, which produced no effects on systemic arterial pressure. Chronotropic effects, judged to be caused by autonomic reflexes in response to the hypotensive effects of the compound, were also statistically greater for dl-verapamil than for d-verapamil. These results demonstrate stereoselective pharmacodynamic effects in vivo of verapamil.

The antiarrhythmic agent disopyramide comprises two enantiomers. In the present study, we examined the effects of the individual enantiomers on in vivo electrophysiology in anesthetized, closed-chest dogs. Six dogs received d-disopyramide, seven received l-disopyramide, and three dogs served as controls. Electrophysiologic measurements were performed at a series of geometrically increasing steady-state plasma concentrations of d- or l-disopyramide. Concentration–response curves were constructed for each electrophysiologic parameter, and the slopes of the regression lines of response versus plasma concentration were compared between enantiomers. Electrophysiologic parameters in the control dogs did not significantly change with time. However, stereoselective electrophysiologic effects were observed, with l-disopyramide being more potent than d-disopyramide in prolonging sinus cycle length, Wenckebach cycle length, and atrioventricular nodal refractoriness (p < 0.05). These findings are consistent with the established increased anticholinergic activity of the d-enantiomer which appeared to offset its local anesthetic or sodium channel inhibiting properties. Interrelationships between the autonomic nervous system and the cardiac electrophysiologic effects of disopyramide may be important in its antiarrhythmic effects.

The enantiomers of WB-4101 were evaluated for their ability to antagonize the a1-adrenoreceptor mediated pressor effect of cirazoline and the a2-adrenoreceptor mediated pressor effect of UK-14,304 in pithed rats. The (S)-stereoisomer of WB-4101 was more potent than the enantiomeric (R)-isomer in antagonizing both cirazoline and UK-14,304. The difference in potency between the enantiomers in blocking cirazoline was 37-fold in contrast to an enantiomeric difference of less than 3-fold for antagonizing UK-14,304. Based on DR2 values (i.e., dose of WB-4101 isomer in mg/kg required to produce a 2-fold rightward shift in the doseresponse curves of cirazoline and UK-14,304) obtained in vivo from Schild regressions, a1/a2 selectivity ratios were calculated. While the (S)-enantiomer displays a 187-fold selectivity for a1-adrenoreceptors, the (R)-enantiomer is only approximately 13-fold selective for a1-adrenoreceptors. These results indicate that the a1- and a2-adrenoreceptor blocking activity of WB-4101 resides predominantly in the (S)-enantiomer and that both enantiomers of WB-4101 are selective a1-adrenoreceptor antagonists in vivo. However the degree of a1-adrenoreceptor selectivity differs for each enantiomer, and the enantiometric activity ratios differ for each a-adrenoceptor subtype.

Disopyramide, an antiarrhythmic agent, is marketed as a racemic mixture of two enantiomers. The racemic drug has unusual pharmacokinetic properties because of its concentration-dependent binding to plasma proteins in the therapeutic plasma concentration range. This study examined, in healthy subjects, the individual pharmacokinetic properties of both total and unbound d-and ldisopyramide in plasma after intravenous administration of each enantiomer separately (1.5mg/kg).Also investigated is the pharmacokinetics of total d-and l-disopyramide in plasma after intravenous administration of a pseudoracemate. Both d-and l-disopyramide are found to exhibit concentration-dependent binding to plasma proteins, with d-disopyramide being more avidly bound at lower concentrations. The stereoselective, concentration-dependent binding to plasma proteins resulted in distinct pharmacokinetic properties when the enantiomers were given together as the pseudoracemate. d-Disopyramide had a lower plasma clearance and renal clearance, a longer half-life, and a smaller apparent volume of distribution than l-disopyramide. However, when the enantiomers were administered separately, there were no differences in the clearance, renal clearance, and volume of distribution between enantiomers calculated from either total or unbound drug concentrations. The results reveal an important pharmacokinetic interaction between the enantiomers of disopyramide when given as a racemic mixture, which may be dose-dependent and is not apparent upon administration of the enantiomers separately.

Preparation of the cis-and trans-4-hydroxy-3-trimethyl-ammoniumtetrahydrofuran and 4-acetoxy-3-trimethylammonium-tetrahydrofuran halides and 3-trimethylammoniumtetrahydrofuran iodide is described. Weak muscarinic activity was noted for the unsubstituted 3-trimethylammoniumtetrahydrofuran salt, being about 1000-fold less potent than acetylcholine. The trans-hydroxy and trans-acetoxy compounds showed even less activity, and the cis-compounds were inactive.

Intravenously infused synthetic chylomicrons have been shown to acquire protein and cholesterol in amounts similar to that found in natural lymph and serum chylomicrons. A comparison of composition of the chylomicrons after giving the fat emulsion intravenously or orally showed that the cholesterol and phospholipid content was similar, regardless of the route given.

Six ring-fluorinated phenytoin analogs were synthesized, and their anticonvulsant activity in the maximal electroshock seizure and subcutaneous pentylenetetrazol assays was determined. 5-(4-Fluoro- phenyl)-5-phenylhydantoin, 5-(3-fluorophenyl)-5-phenylhydantoin, and 5,5-bis(4-fluorophenyl)hydantoin were active in the maximal electroshock seizure assay. The compounds were much less potent than phenytoin but showed an extremely long duration of action.

□ 1,1-Diethoxy-3-(1-naphthoxy)-2-propanol (V), the diethyl acetal of an important aldehyde intermediate in the metabolic N-deal-kylation of propranolol, was prepared from compound X, the product of the reaction of the lithium salt of methyl methylsulfinylmethyl sulfide with 2-(l-naphthoxy)-acetaldehyde. Compound X, as a mixture of three diastereomeric α-hydroxydithioacetal derivatives, when treated with ethyl orthoformate afforded the desired acetal V as well as two ring-closure products, the dihydronaphtho[l,2-b]pyrans VI and VII. Compounds VI and VII were characterized on the basis of mass spectral and 1H- and I3C-NMR data. The stereochemistry of these compounds was assigned on the basis of the 300-MHz 1H-NMR spectra of their acetate esters (XI and XII).

Preparation of 6-endoand 6-exo-acetoxy-2-methylisoquinuclidine methiodides are described. Muscarinic assay data are reported. Neither of the compounds showed activity when compared to acetylcholine and 3-acetoxyquinuclidine methiodide.

The syntheses of endo- and exo-2-trimethylammonium-exo-5,6-epoxy-7-oxabicyclo[2.2.1]heptane iodides are reported. Muscarinic assay results are reported and compared with endo-and exo-2-trimethylammoniumbicyclo[2.2.1]heptane iodides. Of the compounds tested, only exo-2-trimethylammoniumbicyclo-[2.2.1]heptane iodide demonstrated muscarinic activity, but it was only marginally active.

Amphetamine analogs 10(e)- and 10(a)-amino-1,2,3,4,4a,9,10,10a-(trans-4a,10a)-octahydrophenanthrene, I and II, respectively, were prepared. Hydrogenolysis (methanolic hydrochloric acid) of 9(a)-hydroxy-10(e)-amino-1,2,3,4,4a,9,10,10a-(trans-4a,10a)-octahydrophenanthrene afforded I. A similar procedure for the preparation of II from 9(a)-hydroxy-10(a)-amino-1,2,3,4,4a,9,10,10a-(trans,-4a,10a)-octahydrophenanthrene was followed, except the more drastic conditions of a mixture of acetic and perchloric acids were necessary. The compounds were inactive when assayed for amphetamine behavioral and hyperthermia effects.

The preparation of 1-methyl-2,3-benzo-6-oxabicyclo[3.2.1]octane-4,7-dione and 1-methyl-2,3-benzo-6-oxabicyclo[3.3.1]nonane-4,7-dione is reported by facile intramolecular cyclization of the corresponding bromotetralone. 4-Methyl-4-carboxyl-1-tetralone is cyclized under the conditions of bromination. 4-Methyl-1-tetralone-4-acetic acid is cyclized only on continued heating of the α-bromoketone in acetic acid.

Abstract. The pharmacokinetics and the endocrine profile of a new low molecular somatostatin derivative, SMS 201–995, were investigated in a group of 35 normal subjects. Clearance studies (n = 6) for this peptide showed a prolonged half-life in plasma, 113 min, following single scinjections of 50 or 100 μg. Arginine stimulation tests (n = 6) were conducted immediately and 180 min after scinjection of 50 μg of SMS 201–995. The stimulatory effect of arginine on GH and insulin was counteracted by the peptide at the P< 0.001 and P< 0.02 significance level, respectively. Delayed arginine stimulation revealed a persistent blockade of the GH release (P< 0.02), whereas a recovery of the insulin response was observed. Plasma glucagon increments following a standard protein meal (n = 10) were significantly (P< 0.001) inhibited by previous scinjection of 50 μg of SMS 201-995. Pretreatment with 50 and 100 μg of SMS 201-995 sc(n = 9) inhibited (P< 0.001) the stimulatory effect of TRH (200 μg iv) on TSH without modifying basal levels. The injection of 100 μg/h during sleep completely abolished the nocturnal GH peak in 4 volunteers. No rebound rise after decline of the suppressive action on GH was recorded in any of the trials.Safety chemistries and blood coagulation studies remained normal and no side-effects or untoward reactions were recorded throughout the investigation.With its high potency, slow plasma clearance, and long action SMS 201–995 may represent a valuable tool in the long-term management of states of inappropriate GH secretion.