Ramoplanin (A-16686), a new glycolipodepsipeptide antibiotic. III. Structure elucidation

By combination of chemical, 1H and 13C NMR, and mass spectrometric studies, the structures of the three components of the antibiotic ramoplanin (A-16686), produced by Actinoplanes sp. ATCC 33076, have been elucidated. All the components have structures formed by a common depsipeptide skeleton carrying a dimannosyl group and are differentiated by the presence of various acylamide moieties, derived from C8, C9 and C10 fatty acids.     

Ramoplanin (A-16686), a new glycolipodepsipeptide antibiotic. IV. Complete sequence determination by homonuclear 2D NMR spectroscopy

Homonuclear 2D NMR spectroscopy double quantum filter correlation spectroscopy (DQF-COSY), relayed-COSY, nuclear Overhauser enhancement spectroscopy (NOESY), and DQF-relayed-NOESY) allowed the complete determination of the core depsipeptide of antibiotic ramoplanin (A-16686). In particular, the DQF-relayed-NOESY experiments were essential in assigning the single signals close to the diagonal.     

The in vitro activity of ramoplanin (A-16686/MDL 62,198), vancomycin and teicoplanin against methicillin-susceptible and methicillin-resistant Staphylococcus spp

Ramoplanin (A-16686/MDL 62,198) is a novel lipoglycopeptide antimicrobial, comprised of three closely related polypeptides containing chlorinated phenyl moieties and D-mannose, isolated from the fermentation products of Actinoplanes sp. ATCC 33076. The antimicrobial activity of ramoplanin is limited to Gram-positive bacteria and its reportedly unacceptable administration side-effects suggest that any potential clinical role will be limited to the topical therapy of superficial skin infections and the eradication of bacteria, representing a possible nosocomial cross-infection source, from carriage sites. In this study the MICs of ramoplanin have been determined for methicillin-susceptible and methicillin-resistant isolates of Staphylococcus aureus, S. epidermidis and S. haemolyticus and compared with those of two glycopeptide antimicrobials, vancomycin and teicoplanin. MICs were determined using an agar incorporation technique in Mueller-Hinton medium with an inoculum of 10(5) cfu. Ramoplanin was 2-8 times more active than either vancomycin or teicoplanin against methicillin-susceptible and methicillin-resistant isolates of S. aureus and methicillin-susceptible isolates of S. epidermidis. Isolates of methicillin-resistant S. epidermidis and both methicillin-susceptible and -resistant isolates of S. haemolyticus were generally less susceptible to teicoplanin than to vancomycin. Ramoplanin was significantly more active than either vancomycin or teicoplanin against these isolates. These results suggest that the clinical evaluation of ramoplanin as a topical antibacterial agent for the control of superficial infections caused by Staphylococcus spp. and for the eradication of methicillin-resistant S. aureus from carriage sites, is justified.     

A-16686, a new antibiotic from Actinoplanes. I. Fermentation, isolation and preliminary physico-chemical characteristics

Actinoplanes sp. ATCC 33076 is a new strain that was found to produce an antibiotic, designated A-16686, which is a complex of three closely-related polypeptides containing chlorinated phenyl moieties and D-mannose. Both the complex and the single fractions possess a good activity against Gram-positive bacteria. A-16686 specifically inhibits the synthesis of the bacterial cell wall.     

Attenuation of defensive analgesia in male mice by 5-HT3 receptor antagonists, ICS 205-930, MDL 72222, MDL 73147EF and MDL 72699.

Recent studies have shown that non-opioid defensive analgesia in male mice is potently inhibited by the 5-HT3 receptor antagonist, ondansetron. The present series of experiments was conducted to further explore the involvement of 5-HT3 receptor mechanisms in this particular form of adaptive inhibition of pain. The drug ICS 205-930 significantly attenuated the reaction at 1.25-2.5 micrograms/kg, with smaller and larger doses being ineffective. Both MDL 72222 and MDL 73147EF produced flat dose-response curves, with significant inhibition of defensive analgesia at minimum effective doses of less than or equal to 10 and 300 micrograms/kg, respectively. Although MDL 72699, the quaternary salt of MDL 72222, also inhibited the reaction, this effect was seen at comparatively large doses (0.5-1.0 mg/kg) only. None of the compounds tested had significant intrinsic effects of tail-flick latencies, over the dose ranges tested. These findings indicate that 5-HT3 receptor mechanisms may have an important modulatory role in certain forms of "stress" analgesia. Data are discussed in relation to the consistent profile of partial inhibition produced by 5-HT3 receptor antagonists in this model.     

Metabolism of the anticoagulant peptide, MDL 28,050, in rats.

Rats were each administered a 9 mg/kg iv bolus dose of a 3H-labeled decapeptide anticoagulant, MDL 28,050. Tritium was eliminated rapidly with approximately 50% of the dose recovered in urine within the first 6 hr. Renal excretion accounted for 68% of the dose, whereas fecal excretion accounted for 16% of the dose. Continuous flow fast atom bombardment mass spectrometry was used to identify the major urinary metabolites of MDL 28,050. Trace amounts of parent drug were found, and other biotransformation products indicated that hydrolysis had occurred at four peptide bonds. Two initial sites of hydrolysis were identified as 4I-5P and 6E-7E, which resulted in the peptide fragments Suc-Y-E-P-I-OH + P-E-E-A-Cha-E-OH and Suc-Y-E-P-I-P-E-OH + E-A-Cha-E-OH, respectively. Further metabolism of these fragments resulted in the N-terminal pentapeptide and the C-terminal dipeptide.     

Pharmacological properties of MDL 19,301: A novel,nonsteroidal, anti-inflammatory agent

Oral administration of MDL 19,301 (N-(1,3-dithiolan-2-ylidene)-4-hexyl-benzenamine) inhibited rat paw edema induced by carrageenan (ED30 4.8 mg/kg) or an Arthus reaction (ED30 8.2 mg/kg p.o.). The oral dose which induced gastric ulceration in 50% of fasted rats (UD50) was greater than 1,000 mg/kg, demonstrating a more favorable therapeutic ratio than conventional nonsteroidal anti-inflammatory agents. Its major metabolite ((MDL16,861, 4[1,3-dithiolan-2-yliden)amino]-benzeneacetic acid) was also a potent inhibitor of carrageenan paw edema (ED50 5.5 mg/kg p.o.), although it was more ulcerogenic (UD50 52 mg/kg p.o.). The anti-inflammatory activity of MDL 19,301, but not that of MDL 16,861, was attenuated by co-administration of an inhibitor of drug metabolism (SK&F525A 30 mg/kg i.p.). This suggests that MDL 19,301 is a prodrug of MDL 16,861 and this phenomenon would explain its lack of ulcerogenicity. Additional anti-inflammatory properties of MDL 19,301 included inhibition of carrageenan pleurisy, adjuvant arthritis, and acetic-acid-induced writhing. Other pharmacological data indicate that MDL 19,301 administration results in inhibition of prostaglandin synthesis; inhibition of arachidonic-acid-induced, but not prostaglandin-E₂-induced, diarrhea in mice; and inhibition of ex vivo arachidonic-acid-induced, but not adenosine-diphosphate-induced, rat platelet aggregation. MDL 19,301 and MDL 16,861 were unexpectedly weak antipyretic agents in rats. In summary, MDL 19,301 is an anti-inflammatory, analgesic prodrug which, unlike conventional agents, is devoid of ulcerogenic activity at therapeutic doses.     

The selective serotonin(2A) receptor antagonist, MDL100,907, elicits a specific interoceptive cue in rats.

Employing a two-lever, food-reinforced, Fixed Ratio 10 drug discrimination procedure, rats were trained to recognize the highly-selective serotonin (5-HT)(2A) receptor antagonist, MDL100,907 (0.16 mg/kg, i.p.). They attained criterion after a mean +/- S.E.M. of 70 +/- 11 sessions. MDL100,907 fully generalized with an Effective Dose (ED)(50) of 0.005 mg/kg, s.c. A further selective 5-HT(2A) antagonist, SR46349, similarly generalized with an ED(50) of 0.04 mg/kg, s.c. In distinction, the selective 5-HT(2B) antagonist, SB204,741 (0.63 and 10.0 mg/kg), the 5-HT(2B/2C) antagonist, SB206,553 (0.16 and 2.5 mg/kg) and the selective 5-HT(2C) antagonists, SB242,084 (2.5 and 10.0 mg/kg,) and RS102221 (2.5 and 10.0 mg/kg), did not significantly generalize. In conclusion, selective blockade of 5-HT(2A) receptors by MDL100,907 elicits a discriminative stimulus in rats which appears to be specifically mediated via 5-HT(2A) as compared with 5-HT(2B) and 5-HT(2C) receptors.     

MDL 27,531 selectively reverses strychnine-induced seizures in mice.

1. Strychnine-sensitive glycine receptors are primarily localized in the brainstem and spinal cord where they are the major mediators of postsynaptic inhibition. A compound which acts functionally like a glycine receptor agonist would be potentially useful as a pharmacological tool and as a therapeutic agent for treating disorders of glycinergic transmission. 2. MDL 27,531 (4-methyl-3-methylsulphonyl-5-phenyl-4H-1,2,4-triazole) blocked strychnine-induced tonic extensor seizures in mice following either intraperitoneal (ED50 = 12.8 mg kg-1; 30 min) or oral (ED50 = 7.3 mg kg-1; 30 min) administration. Time course studies revealed a maximal effect at 30-60 min, though significant activity was still seen after 24 h. 3. MDL 27,531 was selective in antagonizing strychnine seizures and little or no activity was seen against seizures produced by other chemical convulsants (bicuculline; quinolinic acid; mercaptopropionic acid); by electrical stimuli (maximal electroshock); or by sensory stimuli (audiogenic seizure susceptible mice). MDL 27,531 blocked pentylenetetrazol-induced seizures with an ED50 = 55 mg kg-1. This profile differed from those of the anticonvulsants diazepam, valproic acid, and diphenylhydantoin. 4. The antagonism of strychnine seizures by MDL 27,531 occurred at doses that did not produce signs of sedation (suppression of spontaneous motor activity), motor ataxia (disruption of rotarod performance), muscle relaxation (inhibition of morphine-induced Straub tail), or CNS depression (potentiation of hexobarbitone sleep time). MDL 27,531 had less side effect potential (as derived from ratios obtained from the above measures) relative to those of the known muscle relaxants diazepam and baclofen.(ABSTRACT TRUNCATED AT 250 WORDS)     

MDL 72832, a selective 5-HT1A receptor ligand, stereospecifically increases food intake

Effects of the enantiomers of MDL 72832, a novel, potent and selective ligand for 5-HT1A sites, were investigated in a test of platable food consumption in partially pre-satiated male rats. (-)-MDL 72832 significantly increased feeding at 0.03 mg/kg s.c., whereas 1.0 mg/kg (+)-MDL 72832 was required to stimulate food intake. The stereospecificity of the effect provides support for a functional role of 5-HT1A receptors in feeding responses.     

Inhibition of dorsal raphe cell firing by MDL 73005EF, a novel 5-HT1A receptor ligand.

The effect of a novel ligand for the 5-HT1A receptor subtype, MDL 73005EF, on the firing rate of serotonergic dorsal raphe neurons was assessed in rat midbrain slices maintained in vitro. Superfusion with MDL 73005EF inhibited neuronal firing in a concentration-dependent manner. Based upon IC50 values, MDL 73005EF was equipotent with buspirone (129 +/- 34 vs. 97 +/- 8 nM, respectively) but significantly less potent than 8-OH-DPAT (8-hydroxy-2(di-n-propylamino)tetralin; 7 +/- 2 nM). Pretreatment with (-)-propranolol (1 microM), a mixed 5-HT1A/B receptor antagonist, blocked by 50% the inhibition of unit activity elicited by MDL 73005EF. Taken together, these data suggest that MDL 73005EF is an agonist at the somatodendritic autoreceptor on dorsal raphe neurons, a 5-HT1A receptor which regulates in part the pacemaker activity of these cells. The results are discussed in the context of receptor reserve, recently proposed to explain apparent discrepancies in the actions of agonists at pre- and postsynaptic 5-HT1A sites.     

MDL 73,147EF, a 5-HT3 antagonist, facilitates latent inhibition in the rat.

Latent inhibition (LI) is a behavioral model of selective attention that has been used to study the attentional deficits seen in schizophrenia. In the present study, we examined the effect of 5-hydroxytryptamine3 (5-HT3) receptor blockade on LI using the conditioned emotional response (CER) procedure. Prior exposure to 20, 30, or 40 stimulus presentations significantly, and almost completely, inhibited the CER to that stimulus. This LI effect was much weaker when only 10 preexposures were given. 1H-indole-3-carboxylic acid, trans-octahydro-3-oxo-2,6-methano-2H-quinolizin-8-yl ester methanesulfonate (MDL 73,147EF), a selective 5-HT3 receptor antagonist, significantly facilitated the LI effect observed after 10 preexposures at 0.1 mg/kg but not at 0.01 mg/kg. The magnitude of this effect was comparable to that observed with the classical neuroleptic haloperidol (0.1 mg/kg). Neither MDL 73,147EF nor haloperidol affected the CER in animals not preexposed to the stimulus. These results strongly corroborate suggestions that 5-HT3 receptor antagonists will be of use in the treatment of schizophrenia.     

The 5-HT2 receptor antagonist, MDL 28,133A, disrupts the serotonergic-dopaminergic interaction mediating the neurochemical effects of 3,4-methylenedioxymethamphetamine.

The selective 5-HT₂ receptor antagonist MDL 28,133A dose dependently blocked the long-term deficits in rat brain 5-HT concentrations produced by the substituted amphetamine analogue 3,4-methylenedioxymethamphctamine (MDMA). This protective effect of MDL 28,133A could be abolished by coadministration of the dopamine precursor, L-dihydroxyphenylalanine (L-DOPA). Electrophysiological experiments demonstrated that the ability of MDL 28,133A to block the MDMA-induced slowing of A⁹ dopaminergic neurons was also sensitive to L-DOPA administration. Both sets of experiments suggest an interaction of MDL 28,133A at the level of dopamine synthesis. Consistent with this explanation, MDL 28,133A antagonized the MDMA-induced stimulation of dopamine synthesis in vivo. MDMA-induced 5-HT release did not reduce the firing rate of dopaminergic neurons as assessed by dopamine depletion following synthesis inhibition with -mcthyl-p-tyrosinc (-MPT). This indicates that the effect of 5-HT₂ receptor antagonists on MDMA-induced dopamine synthesis is not due simply to the removal of an inhibitory serotonergic input followed by an increase in dopamine cell firing and autoreceptor activation. MDL 28,133A was also shown to be without effect on the sensitivity of terminal dopamine autoreceptors. The results are consistent with the hypothesis that 5-HT₂ receptors are permissive for the stimulation of dopamine synthesis necessary to support MDMA-induced transmitter efflux.     

Antileishmanial activity of MDL 28170, a potent calpain inhibitor

Several calpain inhibitors are under development and some are useful agents against important human pathogens. We therefore investigated the effect of MDL 28170, a potent calpain inhibitor, on the growth of Leishmania amazonensis. After 48 h of treatment, the inhibitor exhibited a dose-dependent antileishmanial activity, with a 50% lethal dose (LD(50)) of 23.3 microM. The inhibitor promoted cellular alterations, such as the parasites becoming short and round. A calpain-like protein migrating at 80 kDa was identified by Western blotting. In addition, the calpain-like molecules were identified on the cell surface of the flagellate. These results add new in vitro insights into the exploitation of calpain inhibitors in treating parasitic infections and add this family of peptidases to the list of potential targets for development of more potent and specific inhibitors against trypanosomatids.     

PHARMACOKINETICS OF MDL 26 479, A NOVEL BENZODIAZEPINE INVERSE AGONIST,IN NORMAL VOLUNTEERS

MDL 26 479 is a new drug undergoing clinical evaluation for the treatment of depression and for memory loss associated with Alzheimer's disease. As part of a dose tolerance trial, the single- (SD) and multiple-dose (MD) pharmacokinetics of MDL 26 479 were evaluated in healthy male volunteers. SDs ranging from 2 to 465 mg, and doses of 30, 60, and 120 mg administered twice daily for 28 d, were examined. Serial blood samples were collected for up to 48 h. Plasma MDL 26 479 concentrations were determined by HPLC. Plasma MDL 26 479 concentration versus time profiles increased rapidly, followed by multiexponential decline. Time to maximum plasma concentration increased over the 230-fold SD range from 0·5 to 3·8 h. Maximum concentrations and areas under the concentration versus time curves increased disproportionately with dose. Apparent oral clearance estimates decreased from 52·9 to 13·8 L h⁻¹. MD pharmacokinetic parameters for doses from 30 to 120 mg were consistent with those observed following SD, thus indicating that SD pharmacokinetics are predictive of MD. SD and MD terminal half-life estimates were similar and independent of dose. ©1997 by John Wiley & Sons, Ltd.     

MDL 27,032 relaxes vascular smooth muscle and inhibits protein kinase C.

The smooth muscle relaxant effect of MDL 27,032, 4-propyl-5-(4-pyridinyl)-2(3H)-oxazolone, was studied in vitro using strips of femoral arteries and saphenous veins from dogs and trachea from guinea pigs. MDL 27,032 (10(-6)-10(-3) M) produced a concentration-dependent relaxation of arterial and venous strips contracted by carbachol. MDL 27,032 also antagonized contractions of arterial and venous strips produced by phorbol 12,13-dibutyrate (PDB), a protein kinase C activator, both in normal-Ca2+ and zero-Ca2+ medium. The compound inhibited protein kinase C in soluble extracts prepared from saphenous veins of dogs, with an IC50 value of 36.6 microM. MDL 27,032 was more effective against the contractions produced by phenylephrine and serotonin than by KCl in arteries, but no such selectivity was noted in veins. MDL 27,032 (10(-3) M) also inhibited accumulation of inositol phosphates in femoral artery but not in saphenous vein, and this effect may have contributed to the arterial-relaxant effect. Because the vascular smooth muscle relaxant effect of MDL 27,032 was endothelium independent, did not involve blockade of alpha-adrenoceptors or inhibition of cyclic nucleotide phosphodiesterases, stimulation of beta-adrenergic receptors, stimulation of adenosine A2-receptors, or activation of K+ channels, these data suggest that the relaxant effects of MDL 27,032 primarily involve inhibition of protein kinase C.     

MDL 72567, a dihydropyridine calcium-antagonist, that causes vasodilation and direct sinus bradycardia

MDL 72567 (2,6 dimethyl,3 methoxycarbonyl,4-(2-nitrophenyl), 5-(2-furoyl)1,4 dihydropyridine) was a potent antagonist of Ca2+-induced contractions in K+-depolarized taenia preparations from the guinea pig caecum (pA2 8.8 +/- 0.1). MDL 72567 was a potent displacer of [3H]nitrendipine binding from rat cortical membrane preparations (Ki 3.99 nM), indicating an effect at the dihydropyridine binding site, which is consistent with the finding that the inhibitory effects of MDL 72567 in smooth muscle were prevented by the dihydropyridine Ca2+ channel activator Bay K 8644. MDL 72567 slowed spontaneously beating rat atria preparations to a greater extent than did nifedipine, however, for a given negative inotropic effect. Furthermore, in pithed rat preparations infused with angiotensin II to elevate blood pressure, the hypotensive effects of MDL 72567 (3 nmol/kg-3 mumol/kg, intravenously, i.v.) were accompanied by bradycardia, whereas nifedipine, PY 108-068, and nicardipine lowered blood pressure without affecting heart rate. When compared with nifedipine, MDL 72567 caused less reflex tachycardia for a given fall in blood pressure, in anesthetized beagles and in conscious renal hypertensive dogs. In anesthetized dogs, MDL 72567 increased cardiac contractility at all hypotensive doses tested (30-3,000 nmol/kg, i.v.), whereas nifedipine caused profound myocardial depression at higher doses (1,000-3,000 nmol/kg, i.v.) even though the compounds had equivalent vasodilator effects. Thus, although MDL 72567 appears to cause a direct myocardial slowing that can partially offset reflex tachycardia, the compound has negligible negative inotropic effects and may therefore be useful in angina pectoris or even in congestive heart failure.