Design,Synthesis,Pharmacological Evaluation,and Druggability Analysis Of Dexmedetomidine Derivatives

Objective:Dexmedetomidine is a highly selective alpha-2 receptor agonist and produces a hypnotic-anesthetic action via activation of central alpha-2 adrenoceptors.It is one of the main sedative drugs used for patient sedation in critical care medicine and anesthesiology.Previous studies showed that dexmedetomidine could reduce the MAC,extend the duration of LORR,produce sedation effect,and have a degree of analgesic effect.Therefore,dexmedetomidine is widely used in in critical care medicine and anesthesiology.However,dexmedetomidine also has some adverse effects like transient vasoconstriction,remarkable hypotension,and bradycardia,when it administrated rapidly or in a large dose.These adverse effects limit the dexmedetomidine widely used for bolus-dose administration or specific clinical scenario sedation.Consequently,research and development of new intravenous general sedatives with fast effecting,better sedation control,high circulation stability,less adverse effects,and high safety is important and valuable.Therefore,in this study,following the original structure of dexmedetomidine,a new series of candidate dexmedetomidine derivatives DA-556#、DA-557#、DA-558#......DA-627# were designed and synthesized based on the design of the target structure.The candidate compounds were screened and evaluated in vivo experiments in animals.The present study was expected to develop and select a compound with fast effecting,better sedation control,less adverse effects,and high safety.Materials and Methods:1.The present study intended to modify and optimize the structure of dexmedetomidine based on the original structureThe research group made related structural modifications about dexmedetomidine without change of the main original structure using other groups that did not affect the main pharmacodynamics to increase the lipid solubility of the compound and increase the efficiency of the compound crossing the blood-brain barrier.This process used computer-aided technology to design and synthesized a series of dexmedetomidine derivatives.After the dexmedetomidine derivatives were designed and synthesized,the nuclear magnetic resonance（NMR）or/and mass spectrum（MS）were used to identify the structure of the new compounds.If the structures designed were the same as the structures synthesized,we tested the pharmacological activities of the new compounds and carried out further researches.2.The pharmacological characteristics and safety of dexmedetomidine derivatives were screened and evaluated1)Development of a screened model according to pharmacodynamics of dexmedetomidine? Dexmedetomidine was bolus-dose administrated via the tail vein in male SD rats,and the ED₅₀ for LORR was identified by up-and-down method.The onset time of LORR,duration of LORR,and duration of sedation were also measured after equivalent dose(2ED₅₀)administration.? The HR,MAP,SAP,and DBP were continuously measured after equivalent dose(2ED₅₀)administration.? Based on sedative-hypnotic effects and hemodynamic characteristics,the screened model for valid candidate compounds was developed.2)Initiatory Pharmacodynamics exploration for candidate compounds The new candidate compounds were administrated via the tail vein,and the ED₅₀ was identified by up-and-down method.The valid candidate compounds were screened for the next experiment.3)The valid candidate compounds were further screened via the screened model? The onset time of LORR,duration of LORR,and duration of sedation of candidate compounds were measured after equivalent dose(2ED₅₀)administration.? The HR,MAP,SAP,and DBP were continuously measured after candidate compounds administration.? The valid candidate compounds were formally selected according to the screened results.4)The pharmacodynamics and safety of valid candidate compounds were evaluated,and the best compound was identified? The primary pharmacodynamics,hemodynamics,heart rate variability,respiratory function in recovery stage,and adverse effects of equivalent-dose(2ED₅₀)valid candidate compounds and dexmedetomidine were evaluated.? The LD₅₀ and TI were also identified in SD rats for valid candidate compounds.? The ED₅₀ for valid candidate compounds and dexmedetomidine were identified in rabbits.The primary pharmacodynamics,hemodynamics,and adverse effects were evaluated after equivalent dose(2ED₅₀)administration.At last,the best compound was selected.3.The analysis for druggability of DA-576#1)The evaluation of pharmacodynamics of equivalent dose(2ED₅₀)in male and female SD ratsThe ED₅₀ of DA-576# for LORR in female SD rats was identified,and the primary pharmacodynamics of equivalent dose(2ED₅₀)were measured and compared with male SD rats.2)The plasma concentration（male SD rats）and pharmacokinetics of DA-576# were identifiedThe arterial blood samples were collected at 1min,2min,5min,10 min,20min,30 min,60min,120 min,180min,and 240 min after DA-576# administrated(three doses: 2ED₅₀,4ED₅₀,and 6ED₅₀).The pharmacokinetic parameters were calculated according to plasma concentration and related information.3)The metabolic pathways and primary metabolites of DA-576# in Monkey and Beagle hepatocytes were explored.4)The exploration for solubleness and appropriate menstruum of DA-576#.4.The initiatory exploration of the mechanism of action via vivo experiments in animalsAlpha-2-receptor antagonists were administrated beforehand in male SD rats and DA-576# or dexmedetomidine were administrated sequentially.The pharmacodynamics of equivalent dose(2ED₅₀)were observed and the mechanism of action was preliminarily speculated or excluded.Results:1.Design and synthesis of new dexmedetomidine derivativesThis study made corresponding modifications to the structure of dexmedetomidine without changing the original main structure.32 new candidate compounds were synthesized and we called them DA-556#,DA-557#,DA-558#......DA-627#.According to the identification with nuclear magnetic resonance（NMR）or/and mass spectrum（MS）,the new candidate compounds were with the same structure as the designed structure.2.The pharmacological characteristics and safety of candidate compounds were screened and evaluated1)Development of a screened model（male SD rats）? The ED₅₀ for LORR was 18.4μg/kg（95% confidence interval=18.1,18.8μg/kg）;the onset time of LORR was 1.1±0.4min,duration of LORR was 64.7±10.8min,and duration of sedation was 72.2±7.2min about commercial preparation.The ED₅₀ for bulk drug was 19.0μg/kg（95% confidence interval=15.4,23.5μg/kg）;the onset time of LORR was 1.6±0.6min,duration of LORR was 75.4±10.7min,and duration of sedation was 89.7±14.8min.? The hemodynamics were continuously measured after equivalent-dose(2ED₅₀)dexmedetomidine administration.HR decreased significantly after administration（vs.baseline,P<0.05）and the descent degree was 40% than baseline.MAP rose fast after administration and started to decrease when it reached the maximum value（30% higher than baseline）（vs.baseline,P<0.05）;the descent degree was 40%,and continuously below baseline（vs.baseline,P<0.05）.SBP and DBP were as the same as MAP.? Therefore,when dexmedetomidine bolus-dose administration,the onset time for LORR was relatively slow,recovery time was significantly slow,sedation control was not good,and the effect of hemodynamics was also significant.2)Initial exploration for pharmacodynamics of candidate compounds? 5 compounds of 32 compounds were identified that had sedative-hypnotic effects in the range of 20mg/kg.? The ED₅₀ values for these 5 compounds were identified via the up-and-down method.3)Valid compounds（DA-575#,DA-576#,DA-592#,DA-601#,and DA-627#）passed the screening via the screened model.Their onset time and recovery time were relatively faster than dexmedetomidine;the performance of sedation control was much better;the hemodynamics were also more stable than dexmedetomidine.Therefore,these 5 candidate compounds passed further screening.4)The pharmacodynamics and safety of 5 candidate compounds were evaluated,and the best compound was identifiedA.Pharmacodynamics for equivalent-dose(2ED₅₀)administration? Primary pharmacology? HemodynamicsBecause of the solvent（DMSO）,the blood pressure decreased briefly and recovered fast to baseline in 3-5min.Therefore,the hemodynamics were still more stable than dexmedetomidine.? Heart rate variabilityThe effects on heart rate variability for these 5 compounds were lighter than dexmedetomidine.? Respiratory function at recovery stageThe effects on related respiratory indexes like respiratory rate,arterial partial pressure of carbon dioxide（Pa CO2）,and arterial oxygen saturation（Sa O2）were also lighter in these 5 compounds.? Adverse effectsNew 5 compounds had different degrees of adverse effects,and DA-576# was with much less and lighter adverse effects than the other 4 compounds.B.Determination and evaluation of LD₅₀ and therapeutic index TIC.The evaluation of pharmacology in rabbits? The ED₅₀ values for LORR in rabbits were also determined via the up-and-down method? The performance of primary pharmacology in rabbits like onset time of LORR,duration of LORR,and duration of sedation was better than dexmedetomidine.The hemodynamics were more stable than dexmedetomidine in rabbits.DA-576# was also with much less and lighter adverse effects than the other 4 compounds.D.After comprehensive consideration and evaluation,DA-576# had a larger potency,LD₅₀ value,TI value,and less adverse effects.Therefore,DA-576# was the selected compound with the best performance in this study.3.The analysis for druggability of DA-576#DA-576# was the best candidate compound after screened and evaluated in this study.We further explored the pharmacodynamics（male and female SD rats）,pharmacokinetics,and solubleness of DA-576# to know more about this new candidate compound.1)The ED₅₀ was 1.7mg/kg（95%CL=1.6,1.9mg/kg）in female SD rats;the onset time for LORR was 0.2±0.2min,the duration of LORR was 3.7±1.3min,and duration of sedation was 13.1±1.1.These pharmacodynamics results were according with male SD rats,the consistency of pharmacodynamics was well.2)Firstly,the HPLC-MS/MS methods for DA-576# were explored and developed.The plasma concentration（male SD rats）and pharmacokinetics of DA-576# were measured and identified.Plasma concentration time data derived from the experiment were analyzed by non-compartmental methods based on statistical moment theory.The pharmacokinetics parameters included AUC（0-t）,AUC（0-∞）,MRT（0-t）,MRT（0-∞）,VRT（0-t）,VRT（0-∞）,t1/2z,Vz,and CLz.3)After LC-MS analysis of the drug DA-576# and the identification of its metabolites,it was speculated that the compound DA-576# was metabolized in monkey and beagle hepatocytes mainly through the metabolic pathways of deoxidation and glucuronic acid binding,with a total of 6 metabolites（serial numbers M1-1,M1-2,M2-2,M3-1,M3-2）.4)Because of the structure design,synthesis,or preparation process,the solubleness of DA-576# was not well like dexmedetomidine.Thus,relatively high-concentration DMSO was needed to dissolve it.Due to the toxicity of DMSO,we tried kinds of methods to look for appropriate menstruum.However,we did not find the appropriate menstruum without toxicity so far.We still seek the applicable menstruum to dissolve the new compound,and ensure the inherent pharmacodynamics.4.The initiatory exploration of the mechanism of action via vivo experiments in animalsBecause dexmedetomidine was a high-selected alpha-2 receptor agonist,and DA-576# was from the modification and optimization of the structure of dexmedetomidine.Therefore,SD rats were preprocessed by selective alpha-2 antagonists and the mechanism of action was speculated or excluded.The results indicated that selective alpha-2 antagonist（Atipamezole）could significantly block the sedation of DA-576# and showed a dose-dependent characteristic.Conclusion:This study modified and optimized the structure of dexmedetomidine,and synthesized a series of new candidate compounds.The pharmacological activity,adverse effects,therapeutic index,pharmacodynamics,and pharmacokinetics of candidate compounds were screened and evaluated,and DA-576# was the selected compound with quick onset time,faster recovery time,better sedation control,less adverse effects,and stable circulatory and respiratory function.Therefore,this compound DA-576# had a good prospect of clinical research and application,and provided a new thought about the development of sedatives.The in vivo experiments in animals indicated that the central alpha-2 receptor was still the main target of the new compound.However,the solubleness of DA-576# was not solved well.This study would further research in this problem to improve understanding about the structure,pharmacological characteristics,medicinal properties,mechanism of action,and solubleness,and we expected that this new compound had a better value of research and development.