Progress toward the development of a safe and effective agent for treating reentrant cardiac arrhythmias: synthesis and evaluation of ibutilide analogues with enhanced metabolic stability and diminished proarrhythmic potential.

A series of ibutilide analogues with fluorine substituents on the heptyl side chain was prepared and evaluated for class III antiarrhythmic activity, metabolic stability, and proarrhythmic potential. It was found that fluorine substituents stabilized the side chain to metabolic oxidation. Many of the compounds also retained the ability to increase the refractoriness of cardiac tissue at both slow and fast pacing rates. The potential for producing polymorphic ventricular tachycardia in the rabbit model was dependent on the chirality of the benzylic carbon. The S-enantiomers generally had less proarrhythmic activity than the corresponding racemates. One compound from this series (45E, trecetilide fumarate) had excellent antiarrhythmic activity and metabolic stability and was devoid of proarrhythmic activity in the rabbit model. It was chosen for further development.

Substituent effects on the antibacterial activity of nitrogen-carbon-linked (azolylphenyl)oxazolidinones with expanded activity against the fastidious gram-negative organisms Haemophilus influenzae and Moraxella catarrhalis.

A series of new nitrogen-carbon-linked (azolylphenyl)oxazolidinone antibacterial agents has been prepared in an effort to expand the spectrum of activity of this class of antibiotics to include Gram-negative organisms. Pyrrole, pyrazole, imidazole, triazole, and tetrazole moieties have been used to replace the morpholine ring of linezolid (2). These changes resulted in the preparation of compounds with good activity against the fastidious Gram-negative organisms Haemophilus influenzae and Moraxella catarrhalis. The unsubstituted pyrrolyl analogue 3 and the 1H-1,2,3-triazolyl analogue 6 have MICs against H. influenzae = 4 microgram/mL and M. catarrhalis = 2 microgram/mL. Various substituents were also placed on the azole moieties in order to study their effects on antibacterial activity in vitro and in vivo. Interesting differences in activity were observed for many analogues that cannot be rationalized solely on the basis of sterics and position/number of nitrogen atoms in the azole ring. Differences in activity rely strongly on subtle changes in the electronic character of the overall azole systems. Aldehyde, aldoxime, and cyano azoles generally led to dramatic improvements in activity against both Gram-positive and Gram-negative bacteria relative to unsubstituted counterparts. However, amide, ester, amino, hydroxy, alkoxy, and alkyl substituents resulted in no improvement or a loss in antibacterial activity. The placement of a cyano moiety on the azole often generates analogues with interesting antibacterial activity in vitro and in vivo. In particular, the 3-cyanopyrrole, 4-cyanopyrazole, and 4-cyano-1H-1,2,3-triazole congeners 28, 50, and 90 had S. aureus MICs

Development of a highly quantitative, reproducible assay for determination of chicken T cell growth factor biological activity.

This report examines optimal culture conditions necessary for accurate and sensitive quantification of chicken T Cell Growth Factor (TCGF) activity. With this bioassay, TCGF is quantified by measuring its ability to cause proliferation of splenocytes prestimulated with mitogen. Proliferation is quantified by determining the optical density (OD) or "signal" of test samples in microtiter wells by measuring the incorporation of tetrazolium salt by live cells. To optimize assay conditions, systematic evaluation of the effects of cell culture variables was carried out with the constant aim of increasing signal to noise ratio in the assay. Higher signal to noise ratios were found when using Dulbecco's Modified Eagle's Medium (DMEM) rather than Roswell Park Memorial Institute Medium (RPMI) for basal tissue culture media containing the same supplements. The addition of lipid supplement to the assay system not only increased the proliferation signal, but also decreased the background OD. Incubation temperatures of 41 C rather than 37 C for both the mitogen prestimulation and proliferation phases of the assay also resulted in a higher signal to noise ratio. While incorporating the optimal experimental conditions, a finalized assay procedure employing test sample normalization with an internal assay standard was tested for accuracy. The assay can accurately detect 2 to 15 U/mL of TCGF activity. The within-assay variation ranged from 2 to 13% and the between-assay variation ranged from 11 to 22% depending upon the TCGF preparation being tested. The excellent reproducibility of this assay has facilitated investigations of TCGF production, processing, and purification.

Pharmacological characterization of novel cyanoguanidines as vascular KATP channel blockers.

KATP blockers derived from cyanoguanidine KATP opener (P1075) chemistry were characterized in isolated rabbit mesenteric artery and evaluated functionally by their ability to antagonize maximal relaxation induced by pinacidil (1 microM) of norepinephrine (5 microM) contraction. PNU-89692, PNU-97025E and PNU-99963 were identified as KATP blockers with IC50 values of 860, 83 and 18 nM, respectively. Studies with selected chiral compounds demonstrated that the (R)-enantiomers were more potent as KATP blockers than the (S)-enantiomers. Further studies demonstrated that PNU-99963 (1) inhibited relaxations by other KATP openers, such as cromakalim (0.5 microM) and minoxidil sulfate (5 microM); (2) was more potent than the other known vascular KATP blockers (glyburide and PNU-37883A); and (3) acted as a KATP blocker in isolated rat aorta as well as dog coronary artery. PNU-99963 actions were selective because PNU-99963 (100 nM) was without any inhibitory effect on relaxations induced by forskolin (0.5 microM), nitroglycerin (1 microM), D600 (25 or 500 nM) or 15 mM K+-induced relaxations of NE contractions in K+-free PSS. The discovery of KATP blockers and openers from the same chemical series is a first for the K+ channel field. The close structural similarity between P1075 (KATP opener) and PNU-99963 (KATP blocker), stereospecificity of action and potency and selectivity all suggest that these molecules may prove to be valuable tools in understanding the structure and function of the KATP channel complex in vascular smooth muscle.

Epithelial cell permeability of a series of peptidic HIV protease inhibitors: aminoterminal substituent effects.

The influence of the aminoterminal substituent in a homologous series of tetrapeptide analogs on transport across Caco-2 cell monolayers was studied. In a series of pyridylcarboxamide regioisomers, the 2-pyridyl isomer was significantly more permeable than either the 3- or 4-congeners. The uniqueness of this peptide was further suggested by examining the partitioning behavior between heptane and ethylene glycol, a system which has been developed as a simple estimate of the desolvation energy or hydrogen bonding potential of a peptide. In this model, the 2-isomer has a much larger partition coefficient than either the 3- or 4-analogs, consistent with its being less solvated than expected based on simple structural considerations. Factors possibly contributing to this decreased effective polarity could be steric interactions or intramolecular hydrogen bonding.

HIV protease (HIV PR) inhibitor structure-activity-selectivity, and active site molecular modeling of high affinity Leu [CH(OH)CH2]Val modified viral and nonviral substrate analogs.

This report details the structure-activity relationships of the HIV gag substrate analog Val-Ser-Gln-Asn-Leu psi[CH(OH)CH2]Val-Ile-Val (U-85548E), an inhibitor exhibiting subnanomolar affinity towards HIV type-1 aspartic proteinase (HIV-1 PR). Our data show that the P1-P2' tripeptidyl sequence provides the minimal chemical determinant for HIV-1 PR binding. We describe the structure-activity properties of Leu psi[CH(OH)CH2]Val substitution in other peptidyl ligands of nonviral substrate origin (e.g., angiotensinogen, insulin and pepstatin). Furthermore, the aspartic proteinase selectivities of a few key compounds are summarized relative to evaluation against human renin, human pepsin, and the fungal enzyme, rhizopuspepsin. These studies have led to the rational design of nanomolar potent inhibitors of both HIV-1 and HIV-2 PR. Finally, a 2.5 A resolution X-ray crystallographic structure of U-85548E complexed to synthetic HIV-1 PR dimer (Jaskolski et al., Biochemistry 30, 1600 [1991]) provided a 3-D picture of the inhibitor bound to the enzyme active site, and we performed computer-assisted molecular modeling studies to explore the possible binding modes of the above series of Leu psi[CH(OH)CH2]Val substituted HIV-1 PR inhibitors.

N-[(omega-amino-1-hydroxyalkyl)phenyl]methanesulfonamide derivatives with class III antiarrhythmic activity.

N-[4-[4-(Ethylheptylamino)-1-hydroxybutyl]phenyl]methanesulfonamid e, (E)-2-butenedioate (2:1) salt (ibutilide fumarate, 2E), has been found to have Class III antiarrhythmic activity. In an in vitro rabbit heart tissue preparation designed to evaluate the cardiac electrophysiology of potential antiarrhythmic agents, it selectively prolongs the effective refractory period of papillary muscle. In vivo it increases the ventricular refractory period of the canine heart and prevents the ventricular arrhythmias induced by programmed electrical stimulation 3-9 days after a myocardial infarction. This paper describes the synthesis of 2E and a series of related compounds. The in vitro evaluation of the cardiac electrophysiology of these compounds has allowed us to determine the structural requirements for Class III antiarrhythmic activity in this series. Evaluation of the antiarrhythmic activity of 2E and one of the more potent analogues on the late postinfarction ventricular arrhythmias induced by programmed electrical stimulation of the canine myocardium is also described. This activity is compared with that of the Class III antiarrhythmic agent sotalol. Compound 2E appears to be as effective and 10-30 times more potent than sotalol in this model.

The evaluation of non-viral substrates of the HIV protease as leads in the design of inhibitors for AIDS therapy.

Scheme 1 summarizes some of what we have learned from this study of non-viral protein substrates of the HIV proteases. Many of these findings contradict the current understanding of protease specificity. P1-P1' amino acids need not be bulky or hydrophobic and residues at these positions may be even less important than those in flanking positions (e.g., Glu at P2') in dictating the course of hydrolysis. Thus, the pattern of amino acids over the whole binding region must be considered in predicting what will or will not be a substrate of these enzymes and, although we are beginning to understand selectivity at the level of primary structure, a detailed explanation of their specificity is yet to be forthcoming. Nevertheless, studies of this kind find useful application in the design of inhibitors of HIV proteases that will, hopefully, be of value in treatment of AIDS.

1-(2-aminoethyl)-6-aryl-4H- [1,2,4]triazolo[4,3-a][1,4]benzodiazepines with diuretic and natriuretic activity.

A series of 1-(2-amino-1-phenylethyl)-6-phenyl-4H- [1,2,4]triazolo[4,3-a][1,4]benzodiazepines was prepared and evaluated for diuretic activity. These compounds have diuretic and natriuretic activity but no kaliuretic activity when evaluated by oral administration to the conscious rat. The structure requirements for this activity are discussed. In particular it was found that the 2-aminoethyl side chain at C-1 with hydrogen or methyl substituents on the amino group was required for diuretic activity. A substituent at C-8 was also required; soft substituents such as methylthio and iodo at this position favored activity. Compounds with both phenyl and 2-pyridyl substituents at C-6 were active; substituents on the C-6 phenyl, however, reduced or eliminated the activity. Substituents other than phenyl at the 1-position of the 2-aminoethyl side chain were detrimental to activity; phenyl substitution at this position was required for activity when the substituent at C-8 was chloro but not when it was bromo.

Design, structure-activity, and molecular modeling studies of potent renin inhibitory peptides having N-terminal Nin-For-Trp (Ftr): angiotensinogen congeners modified by P1-P1' Phe-Phe, Sta, Leu psi[CH(OH)CH2]Val or leu psi[CH2NH]Val substitutions.

A structure-conformation-activity investigation of several angiotensinogen (ANG) based inhibitors of human renin modified by either Phe-Phe, Sta, Leu psi[CH2NH]Val, or Leu psi[CH(OH)CH2]Val at the P1-P1' clevage site and P5 Trp(Nin-For) (Ftr) was performed. Specifically, Ac-Ftr-Pro-Phe-His-Phe-Phe-Val-Ftr-NH2 (1) provided a potent (KI = 2.7 X 10(-8) M) P1-P1' Phe-Phe substituted renin inhibitor to initiate these studies. Substitution of the P1-P1' Phe-Phe in compound 1 by Sta effected a 1,000-fold increase in biological potency for the resultant octapeptide Ac-Ftr-Pro-Phe-His-Sta-Val-Ftr-NH2 (10; KI = 6.7 X 10(-11) M). Kinetic analysis of compound 10 showed it to be a competitive inhibitor of human renin catalyzed proteolysis of human ANG. Chemical modifications of the compounds 1 and 10 were evaluated on the basis of comparative human plasma renin inhibitory activities (IC50 values) in vitro. Carboxy-terminal truncation studies on compound 10 showed that the P2' Val and P3' Ftr residues could both be eliminated without significant loss (ca. 10-fold) in renin inhibitory activity as exemplified by the pentapeptide Ac-Ftr-Pro-Phe-His-Sta-NH2 (12; IC50 = 3.8 X 10(-9) M). In addition, the corresponding P1-P1' Leu psi[CH(OH)CH2]Val and Leu psi[CH2NH]Val derivatives of compound 12 were potent renin inhibitors: Ac-Ftr-Pro-Phe-His-Leu psi[CH(OH)CH2]Val-NH2 (13; IC50 = 3.1 X 10(-10) M) and Ac-Ftr-Pro-Phe-His-Leu psi[CH2NH]Val-NH2 (14; IC50 = 2.1 X 10(-8) M). The structure-conformation-activity properties of the N-terminal Ftr substitution of these human renin inhibitors was examined by (1) comparative analysis of several analogues of 1 and Ac-Ftr-Pro-Phe-His-Sta-Ile-NH2 (17; IC50 = 1.0 X 10(-10) M) having P5 site modifications by Trp, His, D-Ftr, and D-His, (2) deletion of the N-terminal Ftr residue from compounds 12 and 17, to provide Ac-Pro-Phe-His-Sta-Ile-NH2 (16; IC50 = 3.1 X 10(-8) M) and Ac-Pro-Phe-His-Sta-NH2 (15; IC50 = 5.6 X 10(-6) M), and (3) computer modeling and dynamics studies of compounds 1 and 17 bound to CKH-RENIN, a simulated human renin model, which were focused on identifying potential intermolecular interactions of their common P5-P2 sequence, Ac-Ftr-Pro-Phe-His, at the enzyme active site.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacological profile of the antidepressant adinazolam, a triazolobenzodiazepine.

Adinazolam, which is a 1-dimethylaminomethyl triazolobenzodiazepine, is an effective anxiolytic agent as defined by suppression of stress-induced increases in plasma corticosteroids. Adinazolam is also an effective antagonist of pentylenetetrazole. The 1-dimethylaminoethyl triazolo analog, U-43,465F, was inactive in the stressed rat test and only weakly active against pentylenetetrazole. Adinazolam and U-43,465F have been previously shown to have antidepressant activity in classical screening tests. They have also been found to potentiate the effect of norepinephrine and this is consistent with the activity of the known antidepressants; U-43,465F was found to be equieffective to imipramine in this test. Adinazolam was also effective; however, the magnitude of the potentiation was not as great. The uptake of norepinephrine was only weakly affected by either compound. Potentiation or uptake of serotonin were not significantly-altered pharmacological factors. Receptor binding studies were negative except at the benzodiazepine receptor. Chronic treatment with adinazolam did not decrease the number of beta-adrenergic receptors in the cerebral cortex of the rat, in contrast to the positive effect of imipramine. The discovery of triazolobenzodiazepines with antidepressant activity is of special interest. These agents will hopefully have lower toxicity than the tricyclic antidepressants and thus possess a more favourable therapeutic index. This would be advantageous in the treatment of depression.

Kinetics and equilibrium of the reversible alprazolam ring-opening reaction.

Alprazolam underwent a facile 1,4-benzodiazepine ring-opening reaction in an acidic aqueous solution to form a benzophenone compound. The reaction was demonstrated by means of UV, IR, and 1H- and 13C-NMR spectroscopy. Its reverse cyclization reaction to alprazolam occurred when an acidic solution was neutralized. Both the ring-opening and the cyclization rate constants were obtained from the overall rate constant measured at 25 degrees over a pH range of 0.5--8.0; the latter was measured by monitoring the UV spectral change of the reaction. Although the equilibrium was favored for the benzophenone compound in acidic solutions, it was possible to directly measure the cyclization rate at three acidic pH values by providing a sink condition for the product, alprazolam, using a biphasic reaction system. The bell-shaped cyclization rate pH profile was interpreted in terms of a change in the rate-determining step. The pH profile of the ring-opening rate showed an inflection point indicating a different reactivity of mono- and dicationic alprazolam. The apparent equilibrium between alprazolam and the benzophenone compound at a given pH was estimated from the rate constants for the ring-opening and cyclization reactions. The results agree with the apparent pKa measured by a conventional UV spectrophotometry and a titration technique. The pKa of monocationic alprazolam, the reactive species for the covalent hydration, was determined from the pH dependence of the initial absorbance when an alprazolam solution is acidified.

6-(Substituted-amino)-4H-s-triazolo[4,3-a][1,4]benzodiazepines and 4-(substituted-amino)-6H-s-triazolo[4,3-a][1,4]benzodiazepines with potential antianxiety activity.

A series of 6-(substituted-amino)-4H-s-triazolo[4,3-a][1,4]benzodiazepines was prepared for pharmacological evaluation, and, because of an interesting chemical isomerization, a similar series of 4-(substituted-amino)-6H-s-triazolo[4,3-alpha][1,4]benzodiazepines was also obtained. Pharmacological evaluation of these compounds demonstrated that8-choloro-1-methyl-6-piperidino-4H-s-triazolo[4,3-a][1,4]benzodiazpin e (10) had interesting activity in tests useful for detecting antianxiety activity, while the corresponding 4-piperidino derivative (15) had little activity in these tests. A brief discussion of a possible mechanism for the isomerization is also included.

8-Chloro-1-methyl-6-phenyl-4H-s-triazolo[4,3-a][1,4]benzodiazepines with substituents at C-4.

A series of 8-chloro-1-methyl-6-phenyl-4H-s-triazolo[4,3-a][1,4]benzodiazepines with substituents at C-4 was prepared and evaluated for antianxiety potential. It was found that substitution at this position generally decreased the activity in this series.

2,4-Dihydro-6-phenyl-1H-s-triazolo[4,3-a][1,4]benzoidiazepin-1-ones with antianxiety and antidepressant activity.

A series of 2,4-dihydro-6-phenyl-1H-s-triazolo[4,3-a][1,4]benzodiazepin-1-ones was prepared and evaluated for central nervous system activity. It was found that the 2-methyl-substituted analogues had interesting activity in tests useful for detecting anxiolytic agents, while N-2 substitution with omega-(dialkylamino)alkyl substituents give compounds with antidepressant potential as well as antianxiety activity.

1-(Aminoalkyl)-6-aryl-4-H-s-triazolo[4,3-a][1,4]benzodiazepines with antianxiety and antidepressant activity.

A series of 1-(aminoalkyl)-6-aryl-4H-s-triazolo[4,3-a][1,4]benzodiazepines has been prepared and evaluated for central nervous system activity. We have found that members of this series have activity in pharmacological test systems designed to detect both anxiolytic and antidepressant activity. Each type of activity could be varied independently by appropriate substituent selections.

6-Aryl-4H-s-triazolo[4,3-a][1,4]benzodiazepines. Influence of 1-substitution on pharmacological activity.

A series of 1-substituted 6-aryl-4H-s-triazolo[4,3-a][1,4]benzodiazepines was prepared and evaluated for central nervous system activity. It was found that electronegative substituents, such as trifluoromethyl, were detrimental to activity in this series. On the other hand, many compounds with electron-donating substituents at C-1 had interesting activity. In addition to showing anxiolytic potential, some were also active in tests useful for detecting antidepressant and antipsychotic activity. Several analogues with 4-methyl-1-piperazinyl and 4-morpholinyl substituents at C-1 were of particular interest.

Pulmonary acid aspiration syndrome: should prophylaxis be routine?

The gastric contents of three groups of patients were aspirated at the beginning and end of anaesthesia. There were 62 prepared patients, 28 emergency patients untreated and 69 prepared patients who were given 15 ml of 0.3 M sodium citrate mixture at the time of premedication. In approximately 50% of both emergency and prepared patients pH of gastric contents initially suggested the risk of developing acid aspiration syndrome, had inhalation occurred. The proportion of untreated patients in whom more than 40 ml of gastric contents was present at induction and when the tracheal tube was removed were 13% and 31% respectively. The risks were greater in those undergoing upper abdominal operations. Sodium citrate, as used in this study, was shown to be an ineffective antacid. The use of Mist. magnesium trisilicate B.P. as preoperative antacid is urged strongly.