A novel S-nitrosocaptopril monohydrate for pulmonary arterial hypertension: H2O and -SNO intermolecular stabilization chemistry

S-nitrosocaptopril (CapNO) possesses dual capacities of both Captopril and an NO donor with enhanced efficacy and reduced side effects. CapNO crystals are difficult to make due to its unstable S-NO bond. Here, we report a novel stable S-nitrosocaptopril monohydrate (CapNO·H₂O) that is stabilized by intermolecular five-membered structure, where one H of H₂O forms a hydrogen bond with O^- of the stable resonance zwitterion Cap-S⁺=N-O^-, and the O in H₂O forms the dipole-dipole interaction with S⁺ through two unpaired electrons. With the chelation and common ion effect, we synthesized and characterized CapNO·H₂O that is stable at 4 °C for 180 days and thereafter without significant degradation. Compared to Captopril, CapNO showed direct vasorelaxation and beneficial effect on PAH rats, and could be self-assembled in rat stomach when Captopril and NaNO₂ were given separately. This novel CapNO·H₂O with low entropy paves an avenue for its clinical trials and commercialization.

RENAL-SELECTIVE DELIVERY AND ANGIOTENSIN-CONVERTING ENZYME INHIBITION BY SUBCUTANEOUSLY ADMINISTERED CAPTOPRIL-LYSOZYME

In previous studies, we have demonstrated that the low molecular weight protein lysozyme can be used as a renal-selective drug carrier for delivery of the angiotensin-converting enzyme (ACE) inhibitor captopril. Typically, such macromolecular drug-targeting preparations are administered intravenously. In the present study, we investigated the fate of captopril-lysozyme following subcutaneous administration, a convenient route for long-term treatment. The absorption from the subcutaneous injection site and renal uptake of lysozyme were determined by gamma scintigraphy in rats. Bioavailability, renal accumulation, and stability of the captopril-lysozyme conjugate were evaluated by high performance liquid chromatography analysis and by ACE activity measurements. Lysozyme was absorbed gradually and completely from the subcutaneous injection site within 24 h and accumulated specifically in kidneys. After subcutaneous injection of the captopril-lysozyme conjugate, higher renal captopril levels and lower captopril-lysozyme levels in urine indicated the improved renal accumulation in comparison with intravenous administration of the conjugate, as well as its stability at the injection site. After both treatments, captopril-lysozyme conjugate effectuated renal ACE inhibition, whereas plasma ACE was not inhibited. In conclusion, our results demonstrate that we can use the subcutaneous route to administer drug delivery preparations like the captopril-lysozyme conjugate.

11C-Radiosynthesis and preliminary human evaluation of the disposition of the ACE inhibitor [11C]zofenoprilat

(4S)-1-[(S)-3-Mercapto-2-methylpropanoyl]-4-phenylthio-L-proline (Zofenoprilat, 2), the active metabolite of the potent ACE inhibitor Zofenopril Calcium (1), was labelled with carbon-11 (t1/2=20.4 min) to evaluate its pharmacokinetics behaviour in human body using Positron Emission Tomography (PET). [11C]2 labelling procedures were based on the use of immobilized Grignard reagent and the acylation of (S)-4-phenylthio-L-proline methyl ester (5) with 11C-labelled methacryloyl chloride, followed by a Michael addition with thiobenzoic acid. The radiochemical yield was 5-10% (EOB, decay corrected) and specific radioactivity ranged from 0.5 to 1.5 Ci/micromol (18.5-55.5 GBq/micromol). Preliminary in vivo human evaluation of [11C]2 showed that the drug accumulates in organs which express high levels of ACE, like lungs and kidneys, and in organs involved in drug metabolism such as the liver and gall bladder. Results of the distribution of [11C]2 showed a measurable concentration of the drug in the target tissues such as the kidney and to a minor extent, the heart, where it can afford organ protection.

HPLC Profile of Captopril Disulfide That Undergoes Reversible cis-trans Conversion among Three Isomers

Peculiarly shaped chromatograms of some compounds that consist of two reversible isomers have been reported. Those of a compound that consists of three reversible isomers are described here. Because disulfide of captopril has two cis-trans convertible bonds, it exists in three forms of cis-cis, cis-trans and trans-trans isomers. The disulfide has produced various HPLC-UV profiles under various conditions, such as three split peaks, three peaks with bridging plateaus and one broad peak. The effect of the column temperature and the eluent flow rate on the profile was investigated and explained by interconversion among three isomers. A profile analysis could provide some kinetic constants of this reaction.

Evaluation of Critical Formulation Factors in the Development of a Rapidly Dispersing Captopril Oral Dosage Form

New methods of manufacture have enabled the creation of novel dosage forms with unique rapid-dispersion properties. This study combines one such technique with a statistical experimental design to develop dosage forms from captopril, an angiotensin-converting enzyme inhibitor used to treat cases of hypertensive emergency. The TheriForm process, a novel microfabrication technique, was used to build the dosage forms in a layer-by-layer fashion. Three key formulation factors were chosen for the design of experiments. A modified central composite design (Box-Behnken design) was used to maximize the efficiency of the experiments. A total of 13 distinct formulations were fabricated and tested, using mannitol as the bulk excipient. In addition, three replicates of the center point were tested to assess variability and experimental error. These formulations were tested for speed of dispersion (flash time), active content, hardness, friability, and moisture absorption. Regression analysis was performed to fit data responses to quadratic equations. Excellent dose accuracy (95% to 102% of target) and content uniformity (between 1.03% to 2.84%) were observed from all experimental formulation batches. As expected, the choice of powder additive (maltitol, maltodextrin, polyvinyl pyrrolidone), level of additive (2.5% to 7.5%), and saturation level of the binder liquid (45% to 65%) were all found to be significant factors for the TheriForm process. The regression analysis suggested that a rapidly dispersing dosage form of optimal physical properties would be obtained when a powder mixture of mannitol (97.5%) and maltitol (2.5%) is used at a saturation level of 45%. In conclusion, rapidly dispersing captopril oral dosage forms were successfully fabricated and tested. A wide range of physical properties, flash time, and hardness, were determined experimentally, and the effects of key formulation factors were identified.

A thioesterase for chemoselective hydrolysis of S-acyl sulfanylalkanoates

[figure: see text] A thioesterase, isolated from a strain of Alcaligenes sp. ISH108, chemoselectively hydrolyzes thiol esters. The application of the enzyme has been demonstrated in the preparation of the antihypertensive agent captopril.

Differential inhibition of platelet aggregation and calcium mobilization by nitroglycerin and stabilized nitric oxide

We compared the mechanisms of the antiplatelet effects of nitroglycerin (NTG) and stabilized nitric oxide (NO). Stabilized NO was in the form of S-nitrosothiols [S-nitroso-albumin (S-NO-Alb) and S-nitrosocaptopril (S-NO-Cap)] or heme-NO [sodium nitro-prusside (SNP)]. The molecular structure of S-NO-Cap was confirmed by mass spectrometry. NTG, SNP, S-NO-Alb, and S-NO-Cap inhibited ADP-induced platelet aggregation dose dependently. The inhibitory IC50 value was 109 microM for NTG, 0.98 microM for SNP, 2.99 microM for S-NO-Alb, and 2.5 microM for S-NO-Cap. NTG (200 microM) released 15.4 microM nitrite anion into platelet-rich plasma (PRP) after 60-min incubation, to which platelets contributed 5.4 microM. On the other hand, SNP and S-NO-Cap released undetectable amounts of NO2- when incubated in either PRP or platelet-poor plasma (PPP). The platelet cytosolic calcium ion (Ca2+) concentration was measured fluorometrically in Fura-2-loaded gel-filtered platelets. Thrombin-induced Ca2+ mobilization was significantly inhibited by 10 microM NTG, SNP, S-NO-Alb, and S-NO-Cap, whereas resting Ca2+ was unaltered. Ca2+ mobilization was inhibited 28.6% by NTG, 91.9% by SNP, 90.0% by S-NO-Alb, and 92.7% by S-NO-Cap. These results demonstrate that NTG is an exogenous donor of NO, but releases it only slowly. On the other hand, SNP and S-nitrosothiols inhibited platelet aggregation by the action of stabilized NO incorporated in their structure and did not release NO. NTG and stabilized NO shared a common mechanism of antiplatelet activity, which involved inhibition of calcium mobilization.

Dual role of S-nitrosocaptopril as an inhibitor of angiotensin-converting enzyme and a nitroso group carrier

The S-nitroso derivatives of captopril can act as an inhibitor of an angiotensin-converting enzyme in the presence of thiol such as glutathione. S-Nitrosocaptopril also rapidly transfers its nitroso moiety to a heme protein, which is presumably the responsible mechanism for the activation of guanylate cyclase. These results suggest that S-nitrosocaptopril may serve as an effective hypotensive agent.

Positron-labeled angiotensin-converting enzyme (ACE) inhibitor: fluorine-18-fluorocaptopril. Probing the ACE activity in vivo by positron emission tomography

To evaluate the feasibility of probing the distribution of angiotensin-converting enzyme (ACE) in vivo using positron emission tomography (PET), 4-cis-[18F]fluorocaptopril (18FCAP) was prepared by the reaction of the triflate 2 with K18F/Kryptofix 222 in MeCN followed by hydrolysis (2 N NaOH). The synthesis time was 1 hr with an average radiochemical yield (EOS) of 12% and a specific activity of greater than 300 Ci/mmol. In vivo biodistribution in rats at 30 min after administration showed high uptakes into organs known to have high ACE concentration (lung, kidney and aorta) and faster clearance of 18FCAP for lung and kidney, compared to the clearance from the aorta. When different amounts of unlabeled 4-cis-fluorocaptopril (SQ 25750) were coinjected in rats, a dose of greater than 5 micrograms/kg decreased the lung uptake by one-half while only 1 microgram/kg decreased the kidney uptake by one-half. In general, the binding in the four tissues studied was saturable with the expected capacity. 18FCAP was administered to a human and displaceable uptake observed in the lung and kidney. The results demonstrate the feasibility of probing ACE in vivo using PET.

Synthesis and angiotensin converting enzyme inhibitory activity of N-carboxymethyldipeptides with omega-(4-piperidyl)alkyl group

The synthesis of a series of novel, potent angiotensin converting enzyme (ACE) inhibitors containing 1(S)-carboxy-omega-(4-piperidyl)alkyl group at the N-terminal of the dipeptide is described. These 1-carboxy-omega-(4-piperidyl)alkyl derivatives possess greater or equivalent in vitro potency and in vivo efficacy than captopril and enalapril. The length (n) of the carbon chain in the omega-(4-piperidyl)alkyl moiety was varied from two to six to investigate the optimal structure for long-acting ACE inhibitors. 1-[N-[1(S)-Carboxy-6-(4- piperidyl)hexyl]-L-alanyl]-(2a,3a beta, 7a beta)-octahydro- 1H-indole-2-carboxylic acid (9b), the most potent member of the series, had an in vivo area under the curve (AUC) of 685, which was calculated by the inhibition of angiotensin I-induced pressor response vs. time curves (0 to 8 h) after p.o. administration.

[Syntheses of [prolyl-U-14C]alacepril and its related compounds]

In order to study the metabolic fate of alacepril, an anti-hypertensive agent, the 14C-labeled compound of alacepril and its related compounds were synthesized. [Prolyl-U-14C]alacepril was synthesized in over-all yield of 32.7-38.0% by the mixed anhydride condensation of L-phenylalanine with [prolyl-U-14C]DU-1163, which had been prepared from L-[U-14C]proline and N-(S-3-acetylthio-2-methylpropanoyloxy)succinimide. [Prolyl-U-14C]captopril and [prolyl-U-14C]DU-1227 were prepared in high yields by hydrolysis of [prolyl-U-14C]DU-1163 and [prolyl-U-14C]alacepril, respectively. [Prolyl-U-14C]captopril-cysteine was synthesized by condensation of [prolyl-U-14C]captopril with cystine S-monoxide in 55.0% yield.

An improved synthesis of captopril

An improved synthesis of captopril using methacrylic acid as the starting material is described. Treatment of methacrylic acid (I) with a hydrogen halide gave the 3-halogeno-2-methylpropanoic acids II and III, which were treated with thionyl chloride to yield the corresponding 3-halogeno-2-methylpropanoyl chlorides IV and V. Treatment of IV or V with L-proline yielded the N-(R,S-3-halogeno-2-methylpropanoyl)-L-prolines VI and VII, which were separated into optically pure R- and S-diastereoisomers using dicyclohexylamine. Treatment of halides of VI or VII with methanolic ammonium hydrosulfide gave captopril in 28% yield.