A NEW SERIES OF POTENT ANALGESICS

Chemoenzymatic Synthesis of Optically Active Ethereal Analog of iso-Moramide-A Novel Potentially Powerful Analgesic †

To develop potent and safer analgesics, we designed and synthesized a novel enantiomerically enriched ethereal analog of (R)-iso-moramide, namely 2-[(2R)-2-(morpholin-4-yl)propoxy]-2,2-diphenyl-1-(pyrrolidin-1-yl)ethan-1-one. The titled active agent can potentially serve as a powerful synthetic opiate with an improved affinity and selectivity toward opioid receptors (ORs). This hypothesis was postulated based on docking studies regarding the respective complexes between the designed ligand and µ-OR, δ-OR, and κ-OR. The key step of the elaborated asymmetric synthesis of novel analog involves lipase-catalyzed kinetic resolution of racemic 1-(morpholin-4-yl)propan-2-ol, which was accomplished on a 10 g scale via an enantioselective transesterification employing vinyl acetate as an irreversible acyl donor in tert-butyl methyl ether (MTBE) as the co-solvent. Next, the obtained homochiral (S)-(+)-morpholino-alcohol (>99% ee) was functionalized into corresponding chloro-derivative using thionyl chloride (SOCl2) or the Appel reaction conditions. Further transformation with N-diphenylacetyl-1-pyrrolidine under phase-transfer catalysis (PTC) conditions using O2-saturated DMSO/NaOH mixture as an oxidant furnished the desired levorotatory isomer of the title product isolated in 26% total yield after three steps, and with 89% ee. The absolute configuration of the key-intermediate of (R)-(−)-iso-moramide was determined using a modified form of Mosher’s methodology. The preparation of the optically active dextrorotatory isomer of the titled product (87% ee) was carried out essentially by the same route, utilizing (R)-(−)-1-(morpholin-4-yl)propan-2-ol (98% ee) as a key intermediate. The spectroscopic characterization of the ethereal analog of iso-moramide and the enantioselective retention relationship of its enantiomers using HPLC on the cellulose-based chiral stationary phase were performed. Moreover, as a proof-of-principle, single-crystal X-ray diffraction (XRD) analysis of the synthesized 2-[(2R)-2-(morpholin-4-yl)propoxy]-2,2-diphenyl-1-(pyrrolidin-1-yl)ethan-1-one is reported.

The consolidation of neuroleptic therapy: Janssen, the discovery of haloperidol and its introduction into clinical practice

The discovery of haloperidol at the end of the 1950s constitutes one of the greatest advances of 20th century psychiatry. This antipsychotic drug has their origin in the research process of central analgesic molecules derived from pethidine and methadone, carried out by the Belgian company Janssen Phamaceutica. After the synthesis of phenoperidine, numerous analogues of this compound were studied, and chemists at Janssen took the decision to substitute the propiophenone group for a butyrophenone group. One of these compounds went the R-1625, a stronger agent with specifically neuroleptic properties but lacking morphine-like activity. This substance was synthesized on the 11th February 1958 and received the generic name of haloperidol because of the two halogenated substitutes incorporated into the molecule. Clinical development of haloperidol was conducted, primarily, by psychiatric research team at the University of Liège that confirmed its efficacy in the treatment of various psychiatric disorders such as acute and chronic paranoid psychosis, mania, or chronic treatment-resistant schizophrenia. Under the brand name Haldol((R)), haloperidol was licensed and marketed in Belgium in October 1959. The direct and differed consequences of its introduction into the psychiatric practice have been multiple, involving different areas of socio-sanitary reality. Moreover, haloperidol has contributed substantially to the development of biological psychiatry and currently neuroscience, because it made possible the development of new experimental models for predicting the effects of antipsychotics, and allowed the postulate of the firsts biological hypotheses about the schizophrenia etiology. Haloperidol has been included in the World Health Organisation's list of essential medicines.

Paul Janssen (1926-2003)

Paul Janssen (1926-2003) performed during fifty Years an intense pharmaceutical research activity. From 1953 to 2003, he discovered numerous new drugs in various fields of pharmacology. He widened the neuroleptic spectrum with haloperidol and risperidone, the opioid one with dextromoramide, fentanyl and its short-life derivates, constipating agents like loperamide, hypnotics, anaesthetics. In the field of anti-infectious agents, he discovered azole antifungals, parasiticides among which levamisole and mebendazole. Other therapeutic classes have been enriched by JANSSEN's works: vasodilatating agents, antihypertensive and anti-allergic drugs, etc. More recently, his research was oriented towards virology namely anti-HIV drugs. When Paul JANSSEN's life ended, his scientific production seemed to be one of the most eminent in the XXth century.

Characterization of dextromoramide (Palfium) abuse by hair analysis in a denied case

By providing information on exposure to drugs over time, hair analysis is useful in verifying the history of drug use. In a clinical case, where drug abuse was denied, it was possible to identify dextromoramide in the hair of the subject. After acid hydrolysis of the hair with 0.1 M HCl, in the presence of SKF 525A as an internal standard, the drug was extracted at pH 8.4 with chloroform-isopropanol-n-heptane (50:17:33 v/v) and quantified by gas chromatography/mass spectrometry. The hair strands were cut into 3 sections of 2.5 cm, corresponding to a growth period of 2 months. Concentrations were 1.09, 1.93 and 1.48 ng/mg from the root to the end, respectively. This is the first report on dextromoramide testing in human hair.

Tissue distribution of dextromoramide in the rat

The tissue distribution of dextromoramide was studied in rats after the intraperitoneal injection of 0.2 mg/kg of the drug. The pattern of distribution was similar at 15, 30, 60 and 90 min, with the highest concentrations being found in the liver and the myocardium, while other organs were not able to concentrate dextromoramide.

Gas chromatographic mass-specific investigation of dextromoramide (Palfium) metabolism in the horse

Dextromoramide (Palfium) was given by intravenous injection to a Thoroughbred horse at a dosage of 20 mg and urine was collected 2, 4, 6 and 8 h after drug administration. Enzymatic hydrolysis of the urine followed by solvent extraction gave a residue which was back-extracted into 0.1 M sulphuric acid. After basification to pH 9 and solvent extraction, the resulting residue was submitted to gas chromatographic-mass spectrometric analysis. Both electron-impact and ammonia chemical-ionization mass spectra were recorded and, based on the observed fragmentation patterns, the principal metabolites in horse urine were shown to be 2,2-diphenyl-3-methyl-4-morpholinobutyramide (compound 2) and the product of hydroxylation of one phenyl ring in dextromoramide (compound 3), respectively. The electron-impact mass spectra of compounds 2 and 3, and of their derivatisation products from oncolumn methylation in the gas chromatograph, are reported.

[Pharmacokinetics of dextromoramide in the surgical patient]

The pharmacokinetics of dextromoramide were studied in nine patients undergoing peripheral vascular surgery. All the patients were anaesthetised with thiopentone and vecuronium. After tracheal intubation, anaesthesia was maintained with 0.5 to 1.5 vol % halothane and a 60%-40% vol nitrous oxide-oxygen mixture. Once the patient's status was stable, a 0.8 mg.kg-1 bolus of dextromoramide was given intravenously. Blood samples were obtained 2, 5, 10, 30, 60, 90, 120, 180, 240, 300, 360, and 420 min afterwards by an arterial catheter. Dextromoramide serum concentrations were measured with high performance liquid chromatography after extraction with an original technique. The pharmacokinetic parameters were calculated by computer using TRIOMPHE. In five patients, a bi-exponential equation best fitted the results, whereas a tri-exponential equation was necessary for the other four. Mean elimination half-life was 215.3 +/- 78.4 min, and the apparent final volume of distribution was 0.58 +/- 0.20 l.kg-1. Hepatic extraction was low, as shown by a mean systemic clearance of 2.0 +/- 0.9 ml.kg-1.min-1. Liposolubility of this drug is the highest of all opiates, with a heptane/water partition coefficient of 12.3. These parameters demonstrate that, in the opiate drug group, dextromoramide has a place apart from the others.

Toxicological findings after fatal dextromoramide injection

A death involving dextromoramide injection is presented. The drug was analyzed in whole blood, bile, stomach contents, kidney, brain and liver. The whole blood concentration was 1526 ng/ml. The results are compared with the existing literature.

Analgesic activity of (+)-1-(3-methyl-4-morpholino-2:2-diphenylbutyryl)pyrrolidine (r.875) in student volunteers

(+)-1-(3-Methyl-4-morpholino-2:2-diphenylbutyryl)pyrrolidine (R.875) raised the threshold to ischaemic pain in healthy human volunteers. The peak effect for all doses was reached after about 2 hr. The drug frequently caused nausea and vomiting but no euphoria. Muscular weakness was experienced by many subjects and was sometimes followed 1 to 2 hr. later by hiccup and muscle twitching, suggesting that R.875 may have an effect on striped muscle.

A new series of potent analgesics: dextro 2:2-diphenyl-3-methyl-4-morpholinobutyrylpyrrolidine and related basic amides. II. Comparative analgesic activity, acute toxicity and tolerance development in rats for R875, morphine, pethidine and methadone

The analgesic activity, acute toxicity and development of tolerance of R875, morphine, pethidine and methadone after subcutaneous administration in rats have been measured. In this animal, R875 is shown to be several times more active than the three other compounds. R875 has a faster onset of action, higher therapeutic ratios and a slower rate of development of tolerance.

Pharmacology of (+)-, (+)-and (-)-2:2-diphenyl-3-methyl-4-morpholino-butyrylpyrrolidine

(±)-2:2-Diphenyl-3-methyl-4-morpholino-butyrylpyrrolidine (R610) is a more active analgesic agent in mice, rats and guinea pigs than morphine. The analgesic activity is due to the (+)-isomer (R875). The (–)-isomer (R898) is nearly inactive. R610 lowers the body temperature to below control levels in immobilised rats, inhibits the respiration in unnarcotised rats, lowers the blood pressure in unnarcotised rats with experimental renal hypertension, and causes mydriasis in mice. It also augments the action of barbiturates in mice. In all these respects the (+)-isomer is the active compound of the racemic mixture. The (–)-isomer is almost as toxic as the (+)-isomer, which has a broader therapeutic margin than the (±)-form. The dosage-toxicity relation of highly active analgesic agents in mice and rats is irregular especially in the lower dosage range.