Acid Diketopiperazine Research Articles

ADMET Polycondensation of Diketopiperazine-Based Dienes. Polymerization Behavior and Effect of Diketopiperazine on the Properties of the Formed Polymers

l-Glutamic acid diketopiperazine ω-alkenyl esters were synthesized and polymerized via acyclic diene metathesis polycondensation chemistry using ruthenium catalysts. The polycondensation of l-glutamic acid diketopiperazine ω-allyl ester (1) was unsuccessful, while the polycondensation of l-glutamic acid diketopiperazine ω-homoallyl ester (2), -pentenyl ester (3), and -hexenyl ester (4) with Grubbs second-generation catalyst and Grubbs−Hoveyda catalyst satisfactorily proceeded to give the corresponding polymers. They exhibited melting temperatures around 150 °C, and possessed crystalline structures similar to that of polyethylene. Dynamic light scattering and differential scanning calorimetric measurements suggested that the polymers formed aggregates in N,N-dimethylformamide, presumably based on hydrogen bonding between diketopiperazine moieties.

Multiple-Dose Pharmacokinetics of Ramipril in Patients with Chronic Congestive Heart Failure

Thirteen patients with chronic congestive heart failure of NYHA class II-III received multiple doses (14 days) of ramipril (5 mg once daily); the concentrations of ramipril and ramiprilat in plasma, as well as ramipril, ramiprilat, glucuronides, diketopiperazine, and diketopiperazine acid in urine were measured at various times for 14 days. One patient dropped out after the first day due to hypotension and another who accidentally received another ACE inhibitor additionally was excluded, so that 11 patients completed the study. Ramipril and ramiprilat in plasma were determined by radioimmunoassay, and ramipril and its metabolites in urine were measured by gas chromatography in the laboratories of Hoechst AG. Peak concentrations of the active substance ramiprilat were reached after about 4 h and amounted to 22.3 +/- 11.1 ng/ml after the first dose, and a peak concentration of 26.6 +/- 10.0 ng/ml was observed 2.5 +/- 1.4 h on average after administration on day 14. Practically no accumulation was observed for ramiprilat; the AUD (0-24 h) values increased from 191.3 +/- 83.1 ng.h/ml for the first study day to 238.3 +/- 98.0 ng.h/ml for day 14. As expected, only very small fractions of the dose were excreted with urine as unchanged ramipril and ramipril glucuronide. Ramiprilat is excreted with urine to a larger extent than is rampiril--on average 6.6 +/- 3.0% on the first day and 12.2 +/- 3.8% on day 14. The total amount excreted increased by 34% on average, and was mainly due to an increased ramiprilat excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary Results of Biliary Excretion of Ramipril After T-Drainage in Cholecystectomy Patients

Four cholecystectomy patients, aged between 52 and 56 years, weighing between 64 and 90 kg, received 5 mg of ramipril as a single dose in order to investigate the pharmacokinetics and excretion pattern of ramipril. All patients had a T-drainage that allowed bile collection. Serum was collected at regular intervals, bile was collected hourly for 6 h followed by a 6- and 12-h fraction, and urine was collected every 2 h for 8 h followed by a 4- and 12-h fraction. The concentrations of ramipril and ramiprilat in serum and ramipril, ramiprilat, ramipril glucuronide, ramiprilat glucuronide, diketopiperazine, and diketopiperazine acid in bile and urine were determined and the amounts excreted in urine and bile over 24 h were calculated. There were great interindividual differences in maximum concentrations as well as in the time to reach maximum concentrations in plasma and bile as well as in the excretion pattern between urine and bile. The highest concentrations in bile were found for diketopiperazine acid (3,080 ng/ml) and ramipril glucuronide (2,414 ng/ml). In general, only minimal amounts of unchanged ramipril (prodrug) were detected in the bile. In the urine, the major metabolites excreted were diketopiperazine acid, ramiprilat, and diketopiperazine in amounts of 537, 188, and 124 micrograms, respectively. In bile, the main substances excreted were diketopiperazine acid and ramiprilat glucuronide, which amounted to 501 and 314 micrograms, respectively. Biliary excretion may be the explanation for the noncomplete urinary recovery of ramipril and its metabolites.

Pharmacokinetics of ramipril in the elderly

Ramipril (HOE 498) is a pro-drug of which the main metabolite (HOE 498 diacid or ramiprilat) is a potent angiotensin converting enzyme inhibitor. Thirteen healthy white volunteers (5 females and 8 males, ages 65 to 76 years) participated in a study to investigate the pharmacokinetics of HOE 498 in the elderly. After administration of 10 mg of HOE 498, sequential urine and serum specimens were obtained for assay of HOE 498 and metabolites (HOE 498-glucuronide, diacid, diacid-glucuronide, diketopiperazine and diketopiperazine acid). Side effects, clinical chemistry and hematology were monitored. HOE 498 reached peak concentrations of 62.4 ± 23.3 ng/ml in serum after 0.7 ± 0.3 hours. Serum levels decreased with an apparent half-life of 0.9 ± 0.4 hours. The diacid was rapidly formed in serum, reaching peak concentrations of 40.6 ± 14.0 ng/ml after 2.0 ± 0.6 hours and declining with a half-life of 2.2 ± 0.5 hours. A prolonged terminal phase of serum concentration versus time curve was observed at concentrations <1 ng/ml. The mean recovery of HOE 498 and metabolites in urine, up to 26 hours after administration, was 35 ± 14% of the dose. The apparent half-lives, calculated from urine parameters, for HOE 498 and the diacid were 2.6 ± 0.9 and 4.0 ± 1.1 hours, respectively. The mean peak concentration and half-life of HOE 498 in serum are slightly higher in the elderly than in younger volunteers. Complete urinary collection was not possible, but urinary recovery did not seem different from younger volunteers.

Influence of renal function on the pharmacokinetics of ramipril (HOE 498)

The pharmacokinetics of ramipril (HOE 498) were studied after oral administration of a single 10 mg dose to 24 hypertensive patients with different degrees of renal function. The creatinine clearance ranged between 4.1 and 126 ml/min/1.73 m 2 and was below 35 ml/min/1.73 m 2 in 16 patients. Angiotensin converting enzyme activity and the concentrations of ramipril and its active diacid metabolite ramiprilat were measured in plasma up to 10 days after drug intake. Urine levels of ramipril, ramiprilat, their glucuronides and 2 major metabolites (a diketopiperazine and a diketopiperazine acid) were measured up to 4 days after medication. The plasma concentration-time curve of ramiprilat was poly-phasic with an initial steep decline after the peak level and a subsequent very long terminal phase at low concentrations. Impaired renal function resulted in higher peak levels of ramiprilat, longer times to peak and a markedly slower decline of plasma ramiprilat levels. Hence, the duration of angiotensin converting enzyme inhibition was considerably prolonged in renal failure and depended on the severity of renal impairment. The urinary excretion of ramipril and its metabolites decreased with decreasing renal function and was linearly related to the creatinine clearance, suggesting an alternative pathway of elimination. The pattern of excretion rates of ramipril and its various metabolites was not affected by renal failure. In contrast to the marked changes in the renal elimination, no relevant differences were observed in the absorption of ramipril from the gastrointestinal tract. Systolic and diastolic blood pressure decreased in all groups. The single 10 mg dose of ramipril was well tolerated.