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YAKUGAKU ZASSHI, 122(12),1011-1035, 2002
Biologically active natural products with unique, highly complex molecular skeletons have been used as leading compounds for raw materials of new drugs. Due to the limitations of natural supply, highly efficient, large-scale syntheses and molecular design have been sought in drug discovery. For this purpose, we have focused on a synthetic strategy effective in developing novel reactions and reagents and found several useful regio- and stereospecific reactions, contributing to the synthesis of otherwise unattainable target molecules. The application of these reactions for the total synthesis of three types of potent cytotoxic natural products for the first time is described in this paper. The basic concept is first described. Then the total synthesis of anthracyclines, fredericamycin A, and discorhabdins is reported. Novel reactions using hypervalent iodine reagents under environmentally benign conditions are also described. The future prospects for this method are discussed.
Key words--daunomycin; 11-deoxydaunomycin; fredericamycin A; discorhabdin A
YAKUGAKU ZASSHI, 122(12),1037-1058, 2002
By incorporating the transporter-mediated or receptor-mediated transport process in physiologically based pharmacokinetic models, we succeeded in the quantitative prediction of plasma and tissue concentrations of β-lactam antibiotics, insulin, pentazocine, quinolone antibacterial agents, and inaperizone and digoxin. The author's research on transporter-mediated pharmacokinetics focuses on the molecular and functional characteristics of drug transporters such as oligopeptide transporter, monocarboxylic acid transporter, anion antiporter, organic anion transporters, organic cation/carnitine transporters (OCTNs), and the ATP-binding cassette transporters P-glycoprotein and MRP2. We have successfully demonstrated that these transporters play important roles in the influxes and/or effluxes of drugs in intestinal and renal epithelial cells, hepatocytes, and brain capillary endothelial cells that form the blood-brain barrier. In the systemic carnitine deficiency (SCD) phenotype mouse model, juvenile visceral steatosis (jvs) mouse, a mutation in the OCTN2 gene was found. Furthermore, several types of mutation in human SCD patients were found, demonstrating that OCTN2 is a physiologically important carnitine transporter. Interestingly, OCTNs transport carnitine in a sodium-dependent manner and various cationic drugs transport it in a sodium-independent manner. OCTNs are thought to be multifunctional transporters for the uptake of carnitine into tissue cells and for the elimination of intracellular organic cationic drugs.
Key words--transporters; P-glycoprotein; intestinal absorption; blood-brain barrier; β-lactam antibiotics; carnitine
YAKUGAKU ZASSHI, 122(12),1059-1080, 2002
The mammalian circadian pacemaker resides in the paired suprachiasmatic nuclei (SCN). Clock genes are the genes that control the circadian rhythms of physiology and behavior. The effectiveness and toxicity of many drugs vary depending on dosing time associated with 24-h rhythms of biochemical, physiological, and behavioral processes under the control of the circadian clock. However, many drugs are still administered without regard to the time of day. Identification of a rhythmic marker for selecting dosing time will lead to improved progress and diffusion of chronopharmacotherapy. The monitoring of rhythmic markers may be useful in choosing the most appropriate time of day for administration of drugs and may increase their therapeutic effects and/or reduce their side effects. On the other hand, several drugs can cause alterations in 24-h rhythms, leading to illness and altered homeostatic regulation. Here, we show the disruptive effect of interferon on the rhythm of locomotor activity, body temperature, and clock gene mRNA expression in the periphery and SCN. The alteration of the clock function, a new concept of adverse effects, can be overcome by devising a dosing schedule that minimizes adverse drug effects on clock function. Furthermore, to produce new rhythmicity by manipulating the conditions of living organs using rhythmic administration of altered feeding schedules or several drugs appears to lead to the new concept of chronopharmacotherapy. One approach to increasing the efficiency of pharmacotherapy is administering drugs at times during which they are best effective and/or tolerated.
Key words--circadian rhythm; clock genes; chronopharmacology; chronopharmacokinetics; chronopharmacotherapy
YAKUGAKU ZASSHI, 122(12),1081-1093, 2002
Artificial molecules that exhibit specific recognition of duplex DNA have attracted great interest because of their potential application in the manipulation of gene expression. Specific chemical reactions to the target base within the predetermined site would secure selective inhibition at either translation or transcription reactions. A more interesting application would be to alter the reacted base structure to induce a point mutation. In our study, we have focused our efforts on: 1) development of new cross-linking molecules with high efficiency as well as high selectivity; 2) establishment of a new molecular basis for the formation of nonnatural triplexes; and 3) synthetic approaches to the new minor groove binders. This paper summarizes our recent results using two new functional molecules: 2-amino-6-vinylpurine derivatives as new cross-linking agents; and W-shaped nucleic acid analogues as new recognition molecules for the formation of nonnatural-type triplexes.
Key words--antisense; antigene; site-directed reaction; cross-linking; 2-amino-6-vinylpurine; triple helix
YAKUGAKU ZASSHI, 122(12),1095-1108, 2002
We report novel supramolecular polyhedrons formed by three-dimensional self-assembly of multinuclear zinc(II)-12-membered tetraamine (=cyclen=1,4,7,10-tetraazacyclododecane) complexes with potentially multidentate ligands such as cyanuric acid (CA) and trithiocyanuric acid (TCA) in aqueous solution. Two new supermolecular frameworks were isolated by self-assembly of a tris (Zn2+-cyclen) (Zn3L1) with di-(CA2−) or tri-deprotonated cyanuric acid (CA3−) in aqueous solution. One was a very stable 2 : 3 complex of Zn3L1and CA2− formed above pH 6, which was stable in aqueous solution at neutral pH. The second was an unexpected supramolecular complex formed by 4 : 4 self-assembly of Zn3L1 and CA3−, which was isolated by allowing a 1 : 1 mixture of Zn3L1 and CA to stand in aqueous solution at pH 11.5. X-ray crystal analysis showed a highly symmetric 4 : 4 assembly complex with a cuboctahedral exterior and an inner hollow, which was schematically represented as a truncated tetrahedron formed by binding four equilateral triangles and four scalene hexagons with each other through CA3−-Zn2+ bonds. The 4 : 4 complex was found to be stable only in solid form or in DMSO solution and tends to revert to the 2 : 3 complex in the presence of H2O. This problem has been overcome by replacing CA with TCA, of which the thioimide functions possess lower pKa values than those of CA. TCA acted as a tridentate donor for three Zn3L1 at neutral pH to yield a similar type of 4 : 4 self-assembling supercomplex, in which the deprotonated TCA3− in an aromatic 1,3,5-triazine binds to Zn3L1 through Zn2+-S−(exocyclic) coordination bonds, and thus the 4 : 4 assembly is a chiral twisted cuboctahedron. More interestingly, this supramolecular capsule was found to be stabilized by encapsulation of various size-matched and hydrophobic guest molecules such as adamantane in the twisted truncated cavity. Finally, we succeeded in synthesizing new supramolecular trigonal prisms from linear multinuclear zinc complexes such as p-Zn2L2 and p,p-Zn3L3 with TCA3− in aqueous solution at neutral pH, which are stabilized by Zn2+-S− or Zn2+-N− coordination bonds and hydrogen bonds in aqueous solution at neutral pH. Thus we discovered a new approach to the design of various supramolecular structures in aqueous solution.
Key words--supramolecular polyhedrons; three-dimensional self-assembly; multinuclear zinc (II) complexes; coordination bonds; aqueous solution; molecular recognition
YAKUGAKU ZASSHI, 122(12),1109-1121, 2002
Pituitary adenylate cyclase-activating polypeptide (PACAP) has been conserved remarkably during evolution and is widely expressed in the nervous system across phyla. PACAP has an amino acid sequence homology of 68%with that of vasoactive intestinal polypeptide (VIP) and of 37%with that of secretin, indicating that PACAP is a member of the VIP/glucagon/secretin superfamily. PACAP exerts its actions via three heptahelical G-protein-linked receptors: one PACAP-specific (PAC1) receptor and two receptors (VPAC1 and VPAC2) shared with VIP. PACAP stimulates several different signaling cascades in neurons, leading to the activation of adenylate cyclase, phospholipase C, and mitogen-activated protein kinase and mobilization of calcium. Although PACAP and VIP have no apparent homology with calcitonin and parathyroid hormone (PTH), PAC1, VPAC, secretin, glucagon, glucagon-like peptide 1, growth hormone-releasing hormone, calcitonin, and PTH/PTH-related peptide receptors are related to each other and constitute a sub family of the G-protein-coupled receptors. Distribution analysis of PACAP and its receptors and pharmacological studies have elucidated its pleiotropic effects in the central and peripheral nervous systems. However, the relevance of the pharmacological PACAP effects to the actual physiological activities of endogenous PACAP has not been addressed, because potent and selective low-molecular-weight PACAP antagonists have not yet been developed. To assess the function of PACAP in vivo, we have recently generated PAC1 receptor- and PACAP-targeted mice, and provided evidence that PACAP plays a previously uncharacterized role in the regulation of psychomotor behaviors. In this review, we focus on the physiological and or pathophysiological roles mediated by PACAP in the nervous system.
Key words--pituitary adenylate cyclase-activating polypeptide (PACAP); vasoactive intestinal polypeptide (VIP); knockout mice; receptor; gene expression; psychomotor behaviors
YAKUGAKU ZASSHI, 122(12),1123-1131, 2002
The peptides related to inactivation of sodium channels were synthesized by the solid-phase method for the purpose of proposing a more precise concept than so far obtained for the inactivation and to determine the main factors that control inactivation. The three-dimensional structures of the peptides were determined using 1H-NMR spectroscopy. It was newly discovered that hydrogen bonding was formed between the amide proton of Ile in the IFM (IFM1488-1490) motif of the III-IV linker and the hydroxyl oxygen atom of the side chain of Thr located adjacent to the IFM motif. This hydrogen bonding characterizes the structure around the IFM motif. By calculating the solvent-accessible surface area of the peptide corresponding to the III-IV linker, it was found that a hydrophobic cluster was formed. The hydrophobic cluster stabilizes the structure of the IFM motif. Moreover, the solvent-accessible surface area of the IFM motif correlated with the sustained currents of the incompletely inactivated sodium channels. The free energy of stabilization by hydrophobic interactions (ΔG, −3.9 kcal mol−1), which is calculated from the solvent-accessible surface area for the IFM motif (195 Å2), was in good agreement with that calculated for the equilibrium between the open and the inactivated states of the sodium channels (−4.1 kcal mol−1). The structure of the III-IV linker peptide in a phosphate buffer also formed a hydrophobic cluster, as well as in SDS micelles, although no hydrogen bonding was formed. This distinction results in the following conformational change in the IFM motif: in SDS micelles, the side chains of Ile and Phe in the IFM motif were directed to the hydrophobic cluster, whereas those in a phosphate buffer were directed opposite to the cluster and solvent exposed. The secondary structures of IIIS4-S5 and IVS4-S5, which are considered to form a receptor site, assumed α-helical conformations around the N-terminal half of the sequences. The residue A1329 in MP-D3, which is considered to interact with F1489 of the IFM motif, was found to locate within the α-helix. A hydrophobic cluster was formed on one side of the helix of MP-D4, which also plays an important role in the inactivation. A new concept for the process of fast inactivation is presented. In response to the voltage-dependent activation and the movement of the S4 segments, the two hydrophobic clusters due to the IVS4-S5 and the III-IV linker interact with each other. This interaction increases the hydrophobicity around the IFM motif. The increased hydrophobicity causes the conformational switching of the IF1488-1489 residues to allow F1489 to interact with A1329 of IIIS4-S5 and/or with N1662 in IVS4-S5. As a consequence of this process, the inactivation gate closes.
Key words--sodium channel; inactivation; solution structure; NMR
YAKUGAKU ZASSHI, 122(12),1133-1143, 2002
Glycosphingolipids (GSLs), together with glycopeptides, are typical constituents of various cell membranes in a wide variety of organisms. In particular, it is known that GSLs have numerous physiological functions due to variations in the sugar chain, in spite of the very small quantity of constituents. Those are classified into cerebrosides, sulfatides, ceramide oligohexosides, globosides, and gangliosides based on the constituent sugars. Gangliosides, sialic acid-containing GSLs, are especially enriched in the brain and nervous tissues and are involved in the regulation of many cellular events. Recently, a number of GSLs have been isolated from marine invertebrates such as echinoderms, poriferans, and mollusks. We have also been researching biologically active GSLs from echinoderms to elucidate the structure-function relationships of GSLs and to develop novel medicinal resources. This review summarizes the structures and biological activities of GSLs from sea cucumbers. This study showed that the characteristics of GSLs and structure-activity relationships had neuritogenic activity toward the rat pheochromocytoma cell line PC12. That is, most of the cerebroside constituents of the sea cucumber are same glucocerebrosides as in other animals, except for some constituents, while the ganglioside constituents were unique in that a sialic acid directly binds to the glucose of cerebroside, they are mutually connected in tandem, and some are located in the internal parts of the sugar chain. It also became apparent that sialic acid is indispensable for the neuritogenic activities.
Key words--echinoderm; sea cucumber; glycosphingolipid; ganglioside; cerebroside; neuritogenic activity
YAKUGAKU ZASSHI, 122(12),1145-1151, 2002
We evaluated the economic efficiency as well as the clinical effectiveness on serum lipid levels of a change in drug therapy from bezafibrate or a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor to fenofibrate. Subjects were 26 outpatients suffering from type IIb or type IV hyperlipidemia who visited our hospital between October 2000 and January 2001. Medication doses, and serum lipid levels were recorded prior to the change to fenofibrate and at 6 months after the change. Medical costs were also calculated at the same time points. A significant reduction in medical costs of 14.9%was observed following the change to fenofibrate. Serum lipid levels were not significantly different, although an increase in low density lipoprotein-cholesterol (LDL-cholesterol) was observed in patients changing from the HMG-CoA reductase inhibitor. The actual drug costs were reduced by 21.8%in the bezafibrate to fenofibrate group and by 23.7%in the HMG-CoA reductase inhibitor to fenofibrate group. Although the drug costs of changing to fenofibrate decreased significantly, other costs remained almost unchanged.
Key words--fenofibrate; economics; bezafibrate; hyperlipidemia; 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor
YAKUGAKU ZASSHI, 122(12),1153-1158, 2002
Twenty percent of dermatologists have experienced a separation of water or deterioration of topical corticosteroids mixed with commercially available ointments and/or creams. However, few investigations of this deterioration of admixtures have been reported. To assess the effects of preservatives in preventing microbial contamination of these admixtures, we attempted to investigate the concentration of preservative agents in admixtures and the microbial contamination of these admixtures with a topical corticosteroid ointment (Antebate®). The concentration of parabens was reduced by half using an admixture of corticosteroid ointment with four types of moisturizing creams, Urepearl, Pastaronsoft, Hirudoid, and Hirudoidsoft. After a further 3 months, no decrease in parabens was seen. No microbial contamination was found in any admixture stored at room temperature for 1 week and touched two times daily with a finger. The concentration and ratio of the parabens in the aqueous phase and oil phase were entirely different in the admixtures before being centrifuged. The aqueous phase of the admixtures of the oil/water (O/W)-type emulsions of Urepearl and Hirudoid was not found to have microbial contamination immediately after being centrifuged. All aqueous phases stored at room temperature or in a refrigerator for 1 week and touched with a finger twice daily exhibited microbial contamination.
These experiments demonstrated that O/W-type emulsions, in which the water easily separates from the bases, should be thoroughly mixed to prevent microbial contamination.Key words--microbial contamination; preservative agent; corticosteroids; admixture; ointment