Design, Synthesis, and Activity Study of Water-Soluble, Rapid-Release Propofol Prodrugs.

In this work, a series of water-soluble propofol prodrugs were synthesized, and their propofol release rate and pharmacodynamic characteristics were measured. We found that inserting glycolic acid as a linker between propofol and the cyclic amino acid accelerated the release of propofol from prodrugs into the plasma while preserving its safety. In animal experiments, prodrugs (3e, 3g, and 3j) were significantly better than fospropofol (the only water-soluble propofol prodrug that has been used clinically) in terms of safety, onset, and duration time of anesthesia. Their molar dose, onset time, and anesthesia duration time were comparable to those of propofol, helping to maintain the clinical benefits of propofol. The experimental results showed the potential of such compounds as water-soluble prodrugs of propofol.

Anesthetic Drug Discovery and Development: A Case Study of Novel Etomidate Analogs.

All currently available general anesthetic agents possess potentially lethal side effects requiring their administration by highly trained clinicians. Among these agents is etomidate, a highly potent imidazole-based intravenous sedative-hypnotic that deleteriously suppresses the synthesis of adrenocortical steroids in a manner that is both potent and persistent. We developed two distinct strategies to design etomidate analogs that retain etomidate's potent hypnotic activity, but produce less adrenocortical suppression than etomidate. One strategy seeks to reduce binding to 11ß-hydroxylase, a critical enzyme in the steroid biosynthetic pathway, which is potently inhibited by etomidate. The other strategy seeks to reduce the duration of adrenocortical suppression after etomidate administration by modifying the drug's structure to render it susceptible to rapid metabolism by esterases. In this chapter, we describe the methods used to evaluate the hypnotic and adrenocortical inhibitory potencies of two lead compounds designed using the aforementioned strategies. Our purpose is to provide a case study for the development of novel analogs of existing drugs with reduced side effects.

Role for the propofol hydroxyl in anesthetic protein target molecular recognition.

Propofol is a widely used intravenous general anesthetic. We synthesized 2-fluoro-1,3-diisopropylbenzene, a compound that we call "fropofol", to directly assess the significance of the propofol 1-hydroxyl for pharmacologically relevant molecular recognition in vitro and for anesthetic efficacy in vivo. Compared to propofol, fropofol had a similar molecular volume and only a small increase in hydrophobicity. Isothermal titration calorimetry and competition assays revealed that fropofol had higher affinity for a protein site governed largely by van der Waals interactions. Within another protein model containing hydrogen bond interactions, propofol demonstrated higher affinity. In vivo, fropofol demonstrated no anesthetic efficacy, but at high concentrations produced excitatory activity in tadpoles and mice; fropofol also antagonized propofol-induced hypnosis. In a propofol protein target that contributes to hypnosis, α1ß2γ2L GABAA receptors, fropofol demonstrated no significant effect alone or on propofol positive allosteric modulation of the ion channel, suggesting an additional requirement for the 1-hydroxyl within synaptic GABAA receptor site(s). However, fropofol caused similar adverse cardiovascular effects as propofol by a dose-dependent depression of myocardial contractility. Our results directly implicate the propofol 1-hydroxyl as contributing to molecular recognition within protein targets leading to hypnosis, but not necessarily within protein targets leading to side effects of the drug.

Synthesis and characterization of novel quick-release propofol prodrug via lactonization.

The water-soluble derivatives of propofol have gained attention as a method to increase solubility of propofol. According to the principle of lactonization, the lead compound HX0969 was synthesized first and then the pharmacological features of HX0969 were evaluated in a comparison with those of propofol in the SD rats. Then, HX0969 disodium phosphate monoester (HX0969W) and glycine ester trifluoroacetic acid salt (HX101230) were synthesized, and their pharmacological features were compared with those of Lusedra®, which has been recognized and marketed as a water-soluble prodrug of propofol since 2008. The results showed that HX0969 could produce an anesthetic effect within a few seconds (3.6±3.0s) and its therapeutic index was 4.66 in the SD rat. The pharmacodynamic characteristics of HX0969W were similar to those of the Lusedra®. HX101230 could still produce an anesthetic effect within 60s in the rats though its therapeutic index was not so high (TI=2.96). Therefore, our study has indicated that HX0969 is a potentially useful lead compound of propofol derivative. Its rapid anesthetic effect is probably associated with lactonization.

Life cycle greenhouse gas emissions of anesthetic drugs.

BACKGROUND: Anesthesiologists must consider the entire life cycle of drugs in order to include environmental impacts into clinical decisions. In the present study we used life cycle assessment to examine the climate change impacts of 5 anesthetic drugs: sevoflurane, desflurane, isoflurane, nitrous oxide, and propofol. METHODS: A full cradle-to-grave approach was used, encompassing resource extraction, drug manufacturing, transport to health care facilities, drug delivery to the patient, and disposal or emission to the environment. At each stage of the life cycle, energy, material inputs, and emissions were considered, as well as use-specific impacts of each drug. The 4 inhalation anesthetics are greenhouse gases (GHGs), and so life cycle GHG emissions include waste anesthetic gases vented to the atmosphere and emissions (largely carbon dioxide) that arise from other life cycle stages. RESULTS: Desflurane accounts for the largest life cycle GHG impact among the anesthetic drugs considered here: 15 times that of isoflurane and 20 times that of sevoflurane on a per MAC-hour basis when administered in an O(2)/air admixture. GHG emissions increase significantly for all drugs when administered in an N(2)O/O(2) admixture. For all of the inhalation anesthetics, GHG impacts are dominated by uncontrolled emissions of waste anesthetic gases. GHG impacts of propofol are comparatively quite small, nearly 4 orders of magnitude lower than those of desflurane or nitrous oxide. Unlike the inhaled drugs, the GHG impacts of propofol primarily stem from the electricity required for the syringe pump and not from drug production or direct release to the environment. DISCUSSION: Our results reiterate previous published data on the GHG effects of these inhaled drugs, while providing a life cycle context. There are several practical environmental impact mitigation strategies. Desflurane and nitrous oxide should be restricted to cases where they may reduce morbidity and mortality over alternative drugs. Clinicians should avoid unnecessarily high fresh gas flow rates for all inhaled drugs. There are waste anesthetic gas capturing systems, and even in advance of reprocessed gas applications, strong consideration should be given to their use. From our results it appears likely that techniques other than inhalation anesthetics, such as total i.v. anesthesia, neuraxial, or peripheral nerve blocks, would be least harmful to the environment.

m-Azipropofol (AziPm) a photoactive analogue of the intravenous general anesthetic propofol.

Propofol is the most commonly used sedative-hypnotic drug for noxious procedures, yet the molecular targets underlying either its beneficial or toxic effects remain uncertain. In order to determine targets and thereby mechanisms of propofol, we have synthesized a photoactivateable analogue by substituting an alkyldiazirinyl moiety for one of the isopropyl arms but in the meta position. m-Azipropofol retains the physical, biochemical, GABA(A) receptor modulatory, and in vivo activity of propofol and photoadducts to amino acid residues in known propofol binding sites in natural proteins. Using either mass spectrometry or radiolabeling, this reagent may be used to reveal sites and targets that underlie the mechanism of both the desirable and undesirable actions of this important clinical compound.

Structure-activity relationship of etomidate derivatives at the GABA(A) receptor: Comparison with binding to 11beta-hydroxylase.

At the GABA(A) receptor, low concentrations of etomidate potentiate the inhibitory effect of GABA on specific binding of the closed channel ligand [(3)H]ethynylpropylbicycloorthobenzoate ([(3)H]EBOB). Here, we present SARs for etomidate and structurally related compounds inducing this effect. In the absence of GABA, similar SARs, but 14-20 times weaker potencies were observed. We discuss these SARs in comparison to the much higher potencies of these compounds as inhibitors of 11beta-hydroxylase.

Synthesis, in vitro and in vivo characterization of novel ethyl dioxy phosphate prodrug of propofol.

A novel ethyl dioxy phosphate prodrug of propofol (3) was synthesized and characterized in vitro and in vivo as safer alternative for phosphonooxymethyl prodrugs. The synthesis of 3 was achieved via vinyl and 1-chloroethyl ether intermediates, followed by addition of phosphate group. Aqueous solubility and chemical stability of 3 was determined in buffer solutions and the bioconversion of 3 to propofol was determined in vitro and in vivo. The results show that 3 greatly enhanced the aqueous solubility of propofol (solubility over 10 mg/mL) and the stability in buffer solution (t1/2=5.2+/-0.2 days at pH 7.4, r.t.) was sufficient for i.v. administration. The enzymatic hydrolysis of 3 to propofol was extremely rapid in vitro (t1/2=21+/-3s) and 3 was readily converted to propofol in vivo in rats. During bioconversion, 3 releases acetaldehyde, a less toxic compound than the formaldehyde released from the phosphonooxymethyl prodrug of propofol (Aquavan), currently undergoing clinical trials. The maximum plasma concentration of propofol, 3.0+/-0.2 microg/mL, was reached within 2.1+/-0.8 min after the i.v. administration of 3. The present study indicates that ethyl dioxy phosphate represents a potentially useful water-soluble prodrug structure suitable for i.v. administration.

Highly water-soluble derivatives of the anesthetic agent propofol: in vitro and in vivo evaluation of cyclic amino acid esters.

Cyclic amino acid esters of propofol were synthesized in an attempt to develop new water-soluble anesthetic agents. Their solubility and stability in aqueous solution, and their ability to release propofol in vitro under physiological conditions were determined. L-Proline (6a) and racemic nipecotic acid (6c) esters were found to be highly soluble in water. Sufficiently stable at physiological pH (half-lives >6 h), the alpha-amino acid esters, 6a and 6b, were found to be quantitatively hydrolyzed in plasma and liver esterase solutions within a few minutes, showing prodrug behavior. The in vitro activity of the esters, determined either by the [(35)S]tert-butylbicyclophosphorothionate ([(35)S]TBPS) binding assay or electrophysiological measurements of the action at cloned human receptors, proved to be a mechanism involving allosteric modulation of GABA(A) receptors. Indeed, L-proline (6a), and racemic pipecolinate (6b) and nipecotate (6c), like propofol, reduced [(35)S]TBPS binding, whereas isonipecotate (6d) showed bicuculline-like behavior, increasing [(35)S]TBPS binding. A nonlinear relation between GABA(A) receptor binding affinity and lipophilicity, as assessed by reversed-phase high-performance liquid chromatography, emerged as a trend. The in vivo anticonvulsant and anesthetic activities of prolinate 6a, intraperitoneally administered in water solution, showed that is a water-soluble propofol prodrug candidate for developing formulations useful for parenteral administration.

Novel water soluble 2,6-dimethoxyphenyl ester derivatives with intravenous anaesthetic activity.

A number of water soluble bis-amino-2,6-dimethoxyphenyl ester derivatives were found to exhibit improved anaesthetic activity in mice relative to propofol 1. Of the analogues disclosed, 44 was further profiled in rodents and found to be a superior agent to propofol for the induction and maintenance of anaesthesia.

Novel alpha-amino-acid phenolic ester derivatives with intravenous anaesthetic activity.

A novel series of alpha-amino-acid phenolic ester derivatives containing sulphide, sulphoxide, sulphone, ester and amide side chains were prepared and shown to display potent intravenous anaesthetic activity.

Narcotic drug methohexital: synthesis by enantioselective catalysis.

The narcotic drug methohexital 1 contains two asymmetric carbon atoms and, thus, consists of four isomers, two diastereomeric pairs of enantiomers. The commercial drug is the so-called alpha-racemate, one pair of diastereomers only. A method was developed to prepare differently enriched mixtures of methohexital isomers without resorting to lengthy and expensive optical resolutions. A model reaction for the synthesis of methohexital is the palladium-catalyzed allylation of 1,5-dimethyl-barbituric acid 3, which is optimized and checked by molecular modeling. Catalysts with the best ligands are used in the allylation of the methohexital precursor 7, which contains the C(6) sidechain at the tetrahedral center of the barbiturate skeleton. The product stereochemistry was determined by the contribution of the enantioselective Pd catalysts and by the fact that the allylation is a kinetic resolution. The methohexital isomer mixtures obtained were evaluated with the corneal stimulus test of rats. Methohexital compositions were found, which are superior to the commercially used alpha-racemate (Brevimytal).

Water-soluble propofol analogues with intravenous anaesthetic activity.

Propofol (2,6-diisopropylphenol) is a widely used intravenous anaesthetic that is formulated as an emulsion since it lacks water solubility. We report a range of water-soluble analogues of propofol, containing a para-alkylamino substituent, which retain good intravenous anaesthetic activity in rodents.