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Biomedical subjects

P Buchwald

Publications and source records attributed to P Buchwald.

At least 19 recordsLinked to original sources
PubMed2002

Targeted drug delivery to the central nervous system via phosphonate derivatives (anionic delivery system for testosterone).

An anionic chemical delivery system (aCDS) has been developed and applied to deliver testosterone (T) to the central nervous system (CNS). The delivery of a target compound is achieved through the use of a specific targetor moiety which is an (acyloxy)alkyl-phosphonate-type functional group. The T-aCDS readily penetrates biological membranes by passive transport due to its increased lipophilicity and enters the target organ. Hydrolytic cleavage by esterases provides a negatively charged, hydrophilic intermediate phosphonate compound (TP-), which is "locked in" the CNS and should provide sustained, site-specific release of the drug. In vitro and in vivo investigations in rats showed that methyl-pivaloyloxymethyl-17-testosterylphosphonate (T-aCDS) might function as an anionic chemical delivery system of testosterone. The concentration of T-aCDS decreased fairly rapidly in vitro. The half-lives (t1/2) in different organs are as follows: blood 4.48 min (r = 0.9388), lung 5.53 min (r = 0.9661), liver 2.82 min (r = 0.9498), and brain 7.37 min (r = 0.9972). Simultaneously with the disappearance of T-aCDS, testosterone-phosphonate (TP-) appeared as a main metabolite in increasing concentration. In vivo evaluations (tail vein 11.3 mg/kg in DMSO) found maximum T-aCDS brain levels 5-10 min after administration; they fell under the borderline of detectability (< 0.1 microgram/g) after 60 min. Maximum concentration of the decomposition product (TP-) was obtained at 30 min after administration; it did not decrease significantly during the study. Even if the phosphonate derivative of the secondary, hindered hydroxyl group in this product was fairly resistant to phosphorolytic attack, the design principle can work for other compounds.

Animals↗
PubMed2002

Physicochemical aspects of the enzymatic hydrolysis of carboxylic esters.

Considering the important role played by enzymatic hydrolysis in the metabolism of therapeutic agents designed by retrometabolic approaches (soft drugs and chemical delivery systems), the present article offers a review of a number of issues related to the enzymatic hydrolysis of carboxylic esters. Current knowledge regarding interorgan- and interspecies variability, stereospecificity, activation energy, proposed mechanism, and quantitative structure-metabolism relationship is summarized. The effects of chain-length and branching in the alcohol or acyl substituent on the rate of hydrolysis in congener series are also summarized. Available in vitro human blood data suggest that shortest half-lives are achieved with sterically non-hindered chains that are neither too short nor too long and are of around four carbon-atom long.

Animals↗
PubMed2001

Attempts of ranking in a series of synthetic nonpsychotropic cannabinoids.

Dexanabinol and other synthetic 6aS-trans cannabinoids are devoid of cannabimimetic activity, as they do not have affinity toward cannabinoid receptors. On the other hand, these compound bind to the NMDA receptor and possess neuroprotective properties. A ranking of 6aS-trans cannabinoids based on their NMDA receptor binding affinity and by using a variety of calculated properties included in a fully computerized expert system has been attempted. The results of the study indicate that either the present isosteric-isoelectronic-based ranking criteria is not adequate to reproduce NMDA receptor binding or that some other members of the series rather than dexanabinol are the true lead compounds of 6aS-trans cannabinoids.

Binding Sites↗
PubMed2001

Receptor binding studies of soft anticholinergic agents.

Receptor binding studies were performed on 24 soft anticholinergic agents and 5 conventional anticholinergic agents using 4 cloned human muscarinic receptor subtypes. The measured pK(i) values of the soft anticholinergic agents ranged from 6.5 to 9.5, with the majority being in the range of 7.5 to 8.5. Strong correlation was observed between the pK(i) s determined here and the pA 2 values measured earlier in guinea pig ileum contraction assays. The corresponding correlation coefficients (r2) were 0.80, 0.73, 0.81, and 0.78 for pK(i) (m1), pK(i) (m2), pK(i) (m3), and pK(i) (m4), respectively. Quantitative structure-activity relationship (QSAR) studies were also performed, and good characterization could be obtained for the soft anticholinergics containing at least 1 tropine moiety in their structure. For these compounds, the potency as measured by the pK i values was found to be related to geometric, electronic, and lipophilicity descriptors. A linear regression equation using ovality (O(e)), dipole moment (D), and a calculated log octanol-water partition coefficient (QLogP) gave reasonably good descriptions (r = 0.88) for the pK(i) (m3) values.

Animals↗
PubMed2001

A simple, predictive, structure-based skin permeability model.

By an extension of our simple, molecular size-based model recently developed to describe octanol-water partition coefficients, we were able to obtain an entirely structure-based model that seems well suited to describe human skin permeability data. The corresponding equations not only eliminate the physicochemical interrelatedness of the parameters of the original Potts & Guy approach that was obtained from similar considerations, but also maintain its elegant simplicity and are consistent with a basic physicochemical model of the related phenomena. As the new model is structure based and fully computerized, it allows direct estimation of skin permeability for any molecule of known structure without the need to obtain octanol-water partition coefficients or other experimental data.

Humans↗
PubMed2001

Structure-metabolism relationships: steric effects and the enzymatic hydrolysis of carboxylic esters.

After a brief review of a number of issues related to the enzymatic hydrolysis of carboxylic esters, scuh as interspecies variability, mechanism, stereospecificity, and activation energy, and after and overview of relevant aspects related to the quantitative modeling of steric effects, the results of a recently developed quantitative structure-metabolism relationship model are discussed. They were obtained for in vitro human blood enzymatic hydrolysis of noncongener esters by introduction of the inaccessible solid angle as a novel measure of steric hindrance.

Animals↗
PubMed2000

Soft drug design: general principles and recent applications.

Soft drug design represents a new approach aimed to design safer drugs with an increased therapeutic index by integrating metabolism considerations into the drug design process. Soft drugs are new therapeutic agents that undergo predictable metabolism to inactive metabolites after exerting their therapeutic effect. Hence, they are obtained by building into the molecule, in addition to the activity, the most desired way in which the molecule is to be deactivated and detoxified. In an attempt to systematize and summarize the related work done in a number of laboratories, including ours, the present review presents an overview of the general soft drug design principles and provides a variety of specific examples to illustrate the concepts. A number of already marketed drugs, such as esmolol, remifentanil, or loteprednol etabonate, resulted from the successful application of such design principles. Many other promising drug candidates are currently under investigation in a variety of fields including possible soft antimicrobials, anticholinergics, corticosteroids, beta-blockers, analgetics, ACE inhibitors, antiarrhythmics, and others. Whenever possible, pharmacokinetic and pharmacodynamic properties are briefly summarized and compared to those of other compounds used in the same field.

Drug Design↗
PubMed2000

Structure-based estimation of enzymatic hydrolysis rates and its application in computer-aided retrometabolic drug design.

After a brief review of the problems related to the description of enzymatic hydrolysis rates and the quantification of steric effects, a recently developed method that uses the inaccessible solid angle omega h calculated around different atoms as a novel steric parameter to estimate human blood in vitro enzymatic hydrolysis rates in noncongener ester series is summarized. Some illustrative results obtained by the integration of this method into the expert system developed for computer-aided soft drug design are also presented. Starting from a lead compound, the system can provide full libraries of possible new "soft" molecular structures, a ranking order of these candidates based on isosteric-isoelectronic analogy to the lead, and estimated hydrolytic half-lives for all structures of interest.

Animals↗
PubMed1999

Quantitative structure-metabolism relationships: steric and nonsteric effects in the enzymatic hydrolysis of noncongener carboxylic esters.

An attempt to quantitatively describe human blood in vitro hydrolysis data for more than 80 compounds belonging to seven different noncongener series of ester-containing drugs is presented. A parameter not yet explored in pharmaceutical studies, the inaccessible solid angle Omega(h), calculated around different atoms was used as a measure of steric hindrance, and the steric hindrance around the carbonyl sp(2) oxygen (Omega(h)(O=)) proved the most relevant parameter. The obtained final equation, log t(1/2) = -3.805 + 0.172Omega(h)(O=) - 10.146q(C=) + 0.112QLogP, also includes the AM1-calculated charge on the carbonyl carbon (q(C=)) and a calculated log octanol-water partition coefficient (QLogP) as parameters and accounts for 80% of the variability in the log half-lives of 67 compounds. A number of structures are still mispredicted, but the equation agrees very well with a recently proposed mechanism for hydrolysis by carboxylesterases. The model, with a predictive power tested here on three unrelated structures, should be useful in estimating approximate rates of hydrolysis for prodrug or soft drug candidates ahead of their synthesis.

Carboxylic Acids↗
PubMed1999

Recent advances in the brain targeting of neuropharmaceuticals by chemical delivery systems.

Brain-targeted chemical delivery systems represent a general and systematic method that can provide localized and sustained release for a variety of therapeutic agents including neuropeptides. By using a sequential metabolism approach, they exploit the specific trafficking properties of the blood-brain barrier and provide site-specific or site-enhanced delivery. After a brief description of the design principles, the present article reviews a number of specific delivery examples (zidovudine, ganciclovir, lomustine benzylpenicillin, estradiol, enkephalin, TRH, kyotorphin), together with representative synthetic routes, physicochemical properties, metabolic pathways, and pharmacological data. A reevaluated correlation for more than 60 drugs between previously published in vivo cerebrovascular permeability data and octanol/water partition coefficients is also included since it may be useful in characterizing the properties of the blood-brain barrier, including active transport by P-glycoprotein.

Journal Article↗
PubMed1999

NMR investigation and secondary structure of domains I and II of rat brain calbindin D28k (1-93).

Calbindin D28k, a member of the troponin C superfamily of calcium-binding proteins, contains six putative EF hand domains but binds only four calcium-atoms: one at a binding site of very high affinity and three calcium-atoms at binding sites of lower affinity. The high-affinity site could be located within domain I while domains III, IV, and V bind calcium less tightly. The recombinant protein construct calb I-II (residues 1-93) comprising the first two EF hands affords a unique opportunity to study a pair of EF hands with one site binding calcium tightly and the second site empty. A series of heteronuclear 2D, 3D and 4D high-resolution NMR experiments were applied to calb I-II, and led to the complete assignment of the 1H, 13C and 15N resonances. The secondary structure of the protein was deduced from the size of the 3JHN-Halpha coupling constants, the chemical shift indices of 1Etaalpha, 13Calpha, 13C' and 13Cbeta nuclei and from an analysis of backbone NOEs observed in 3D and 4D NOESY spectra. Four major alpha-helices are identified: Ala13-Phe23, Gly33-Ala50, Leu54-Asp63, Val76-Leu90, while residues Ala2-Leu6 form a fifth, flexible helical segment. Two short beta-strands (Tyr30-Glu32, Lys72-Gly74) are found preceding helices B and D and are arranged in an anti-parallel interaction. Based on these data a structural model of calb I-II was constructed that shows that the construct adopts a tertiary structure related to other well-described calcium-binding proteins of the EF-hand family. Surprisingly, the protein forms a homodimer in solution, as was shown by its NMR characterization, size-exclusion chromatography and analytical ultra-centrifugation studies.

Amino Acid Sequence↗
PubMed1998

Octanol-water partition of nonzwitterionic peptides: predictive power of a molecular size-based model.

A remarkably simple, molecular size-based model developed to predict octanol-water partition coefficients for organic compounds is tested on a set of 188 neutral peptides with available experimental partition data. Despite using only two parameters, it gives a promising correlation (r2 = 0.914; sigma = 0.455, F = 1978.0), and predictions are in a realistic range even for larger peptides (cyclosporin, melanotan, sandostatin) where common, overparametrized fragment methods become quite unreliable. Ion-pair partitioning and the extraction constant formalism is briefly reviewed to describe the sigmoidal lipophilicity profile of ionizable, nonzwitterionic peptides. It seems possible to extend the present model to estimate apparent partition coefficients measured around neutral pH and physiological conditions for monoionic peptides; however, as no standard conditions are yet defined and only relatively small number of experimental data are available, the situation here is more complex.

Models, Molecular↗
PubMed1998

Computer-assisted design of new drugs based on retrometabolic concepts.

Retrometabolic drug design approaches incorporate metabolic and toxicological considerations into the drug design process and represent a novel, systematic methodology for the design of safe compounds. Two major design concepts aimed to increase the therapeutic index (the activity/toxicity ratio) of drugs were developed. Chemical delivery systems (CDS) are primarily used to allow targeting of the active biological molecules to specific target sites or organs based on predictable enzymatic activation. Soft drug approaches are used to design new drugs by building in the molecule, in addition to the activity, the most desired way in which the molecule is to be deactivated and detoxified subsequent to exerting its biological effects. Special computer programs were developed that starting from a lead compound generate complete libraries of possible soft analogs and then help ranking these candidates based on isosteric-isoelectronic comparisons, predicted solubility/partition properties, and estimated metabolic rates. The novel field of large peptide-CDSs imposes special challenges, but a new, remarkably simple model was developed to estimate partition properties for a wide range of compounds, including quite large peptide derivatives. A suggested change of about five order of magnitudes in the distribution coefficient can explain the "lock in" mechanism of brain-targeting delivery systems.

Animals↗
PubMed1998

Octanol-water partition: searching for predictive models.

The log n-octanol/water partition coefficient (log Po/w) still represents one of the most informative physicochemical parameters available to medicinal chemists. In the present work, principles, methodologies, and parameters are briefly reviewed for a variety of models developed to predict this parameter based on molecular structure. To include the developments of recent years, a total of more than 40 different approaches are mentioned with relevant bibliography within four major categories: group contribution methods, atomic contribution methods, molecular methods, and other physicochemical methods. To underscore once more the utility of this partition coefficient, a comprehensive and reevaluated correlation between log Po/w and in vivo permeability data of rat brain capillaries is included. Most deviants that fell below the trendline are those that have been recently found to be substrates for P-glycoprotein, a multidrug transporter that actively removes them from the brain. Accurate predictions of log Po/w may necessitate many parameters, but there is mounting evidence that molecular size and hydrogen bonding ability can account for a major part of the variance. Our recently developed, molecular size-based approach is reviewed, and it is argued that introduction of three-dimensionality allows the elimination of many empirically derived fragment constants without a significant deterioration of the predictive accuracy. A comparison of predictive power for six different methods on 145 molecules of interest for medicinal chemists is also included.

Animals↗
PubMed1993

Characterization of a polyclonal antiserum against the purified human recombinant calcium binding protein calretinin.

We have purified recombinant human calretinin (CR) from Escherichia coli lysates and have produced a polyclonal antiserum against it. The antiserum recognizes determinants conserved in fish, chicken, rat, monkey and human CR. We show its use in the qualitative detection of CR by different methods of immunohistochemistry as well as in the detection of CR on immunoblots.

Amino Acid Sequence↗
PubMed1992

Two novel human pancreatic lipase related proteins, hPLRP1 and hPLRP2. Differences in colipase dependence and in lipase activity.

We have isolated cDNAs coding for two novel human pancreatic lipase (hPL)-related human proteins, referred to as hPL-related proteins 1 and 2 (hPLRP1 and hPLRP2) and for hPL. The two novel proteins show an amino acid sequence identity to hPL of 68 and 65% for hPLRP1 and 2, respectively. All three proteins are secreted into the medium after transfection of COS cells with the corresponding cDNAs. The size of the three expressed proteins is similar and ranges between 45 and 50 kDa. The expressed hPLRP2 shows a lipolytic activity that is, however, in contrast to that of hPL only marginally dependent on the presence of colipase, whereas hPLRP1 shows no activity in this assay. A Northern analysis of normal human pancreas mRNA shows that the expression levels of hPLRP1 and hPLRP2 are about 4-fold and 24-fold lower, respectively, than that of hPL. hPLRP2 is, additionally, most closely related to a lipase reported to be expressed in mouse T-cells. A comparison of the sequences of the three proteins with sequences described as pancreatic lipases of other animal species shows three subfamilies of closer kinship. This suggests that the two novel proteins also exist in other species and that some of the sequences reported to be pancreatic lipase might more likely be the orthologues of hPLRP1 or hPLRP2 in those species.

Amino Acid Sequence↗
PubMed1991

Immunological identification of yeast SCO1 protein as a component of the inner mitochondrial membrane.

The SCO1 gene of Saccharomyces cerevisiae encodes a 30 kDa protein which is specifically required for a post-translational step in the accumulation of subunits 1 and 2 of cytochrome c oxidase (COXI and COX-II). Antibodies directed against a beta-Gal::SCO1 fusion protein detect SCO1 in the mitochondrial fraction of yeast cells. The SCO1 protein is an integral membrane protein as shown by its resistance to alkaline extraction and by its solubilization properties upon treatment with detergents. Based on the results obtained by isopycnic sucrose gradient centrifugation and by digitonin treatment of mitochondria, SCO1 is a component of the inner mitochondrial membrane. Membrane localization is mediated by a stretch of 17 hydrophobic amino acids in the amino-terminal region of the protein. A truncated SCO1 derivative lacking this segment, is no longer bound to the membrane and simultaneously loses its biological function. The observation that membrane localization of SCO1 is affected in mitochondria of a rho0 strain, hints at the possible involvement of mitochondrially coded components in ensuring proper membrane insertion.

Amino Acid Sequence↗