A three-dimensional view of ligand-receptor recognition at the atomic level is crucial to understand the molecular mechanism of receptor activation. This review describes the structure-function relationships of two receptors important for pharmaceutical science. Granulocyte colony-stimulating factor (G-CSF) is the principal growth factor regulating the maturation, proliferation, and differentiation of the precursor cells of neutrophilic granulocytes. We have determined the crystal structure of G-CSF complexed to the BN-BC domains, the principal ligand binding region of the G-CSF receptor. In a novel oligomerization scheme, the two receptor domains complex in a 2:2 ratio to the ligand, with a noncrystallographic pseudo-two-fold axis through primarily the interdomain region and secondarily the BC domain. This first structural view of a gp130-type receptor-ligand complex presents a new molecular basis for cytokine-receptor recognition. The metabotropic glutamate receptors (mGluRs) are key receptors in the modulation of excitatory synaptic transmission in the central nervous system. Three different crystal structures of the extracellular ligand-binding region (LBR) of mGluR1 have been determined, in a complex with glutamate and in two unliganded forms. They all showed disulfide-linked homo-dimers, of which the “active” and “resting” conformations are modulated through the novel dimeric interface by a packed α-helical structure. The bilobed protomer architectures flexibly change their domain arrangements between an “open” or “closed” conformation. Glutamate binding stabilizes both the “active” dimer and “closed” protomer in dynamic equilibrium. Four domain movements within the dimer affect the separation of the transmembrane and intracellular regions and thereby activate the receptor.
This review describes new knowledge on reactivities and syntheses of N-containing aromatics and their application to the synthesis of natural products covering three subjects. 1) The first part describes the Fischer indole synthesis of o-substituted phenylhydrazones, its mechanism, Reissert indole synthesis, a new synthetic approach from pyrrole to indole, some reactions of indoles (i.e., etc.), acylation, bromination, debromination, debenzylation, Vilsmeier-Haack reaction, and synthesis of 4-methoxy-β-carboline alkaloids. 2) The second part describes a new method of introduction of allyl and vinyl groups on the indole nucleus by means of a Pd catalyst. This method was applied to the synthesis of optically active ergot alkaloids. 3) The third part describes the synthesis of o-substituted diacylanilines and its application to chemoselective acylating reagents. A study on axial chirality based on the Ar-N axis is also involved.
Alkynes react with commercially available Co2(CO)8 to give the corresponding alkyne-Co2(CO)6 complexes. Similarly, treatment of arenes with Cr(CO)6 produces arene-Cr(CO)3 complexes. By taking advantage of the intriguing properties of these metal carbonyl complexes, we developed some selective reactions. In this review, the following topics are discussed: (i) development of selective reactions based on alkyne-Co2(CO)6 complexes; (ii) development of selective reactions based on arene-Cr(CO)3 complexes; and (iii) their application to syntheses of bioactive compounds.
Insulin resistance is a characteristic feature of type II diabetes as well as obesity. This insulin resistant state at the peripheral tissue level causes impaired glucose utilization, leading to hyperglycemia. Studies of antidiabetic agents by Takeda originated more than three decades ago when KK mice were introduced, followed by the development of a highly insulin-resistant animal model, KKAy mice. The first 2,4-thiazolidinedione derivative AL-321, which exhibited hypoglycemic effects in KKAy mice, was discovered by modification of the hypolipidemic agent AL-294 as a lead compound. Extensive structure-activity relationship studies on the analogues of AL-321 led to the selection of ciglitazone (ADD-3878) as a candidate for clinical evaluation. Ciglitazone, a prototypical compound in the series, was shown to normalize hyperglycemia, hyperinsulinemia, and hypertriglyceridemia in various insulin-resistant animal models without altering normoglycemia in nondiabetic animal models. However, it appeared that a more potent compound was needed for further clinical evaluation of this class of compound. Further study of this series of compounds led to the finding of pioglitazone (AD-4833) as a promising clinical candidate. Pioglitazone clearly ameliorates the abnormal glucose and lipid metabolism in diabetic patients and was marketed in the USA in August 1999 for the treatment of type II diabetes. Pioglitazone is now marketed in more than 40 countries world wide. Historical aspects of our studies on pioglitazone and its biological activities are described.
Recently, solid-phase synthesis has been recognized as an important methodology for combinatorial chemistry or automated synthesis directed at drug discovery. Various synthetic methodologies have been applied to solid-phase synthesis, although it appears that organometallic chemistry in this area is still being explored. In solution-phase chemistry, organometallic reagents have been utilized for various molecular transformations, especially selective carbon-carbon bond formation. Metallation chemistry is considered to be an important area of organometallic chemistry. Lithiation has been most widely used for metallation, although the reaction conditions must be strictly controlled to avoid various side reactions. Chemoselective transformation was carried out using the newly developed halogen-zinc exchange reaction of aromatic halides using lithium trialkylzincate. This reaction shows high chemoselectivity and compatibility with alkoxycarbonyl or nitro groups. A highly selective hydrogen-zinc exchange reaction was also developed. In solid-phase organometallic chemistry, an immobilized iodobenzoate was used as a substrate and the halogen-zinc exchange reaction was investigated. The exchange reaction was found to proceed smoothly. As an application of the reaction, various transformations on polymer support were investigated using transmetallation and cyclization. The palladium-catalyzed coupling reaction on polymer support was also investigated, and new cyclization for condensed heteroaromatic compounds was developed. The methodology described here is considered to contribute to expanding the application spectrum of solid-phase organometallic chemistry.
The chemical constituents of Aconitum yesoense var. macroyesoense and Aconitum japonicum were examined using high-resolution spectral analysis. Twelve novel alkaloids were isolated from A. yesoense var. macroyesoense together with 20 known alkaloids. Eight novel alkaloids were isolated from A. japonicum together with 15 known alkaloids. An HPLC-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS) method was useful for the simultaneous determination of 21 Aconitum alkaloids found in A. yesoense var. macroyesoense and A. japonicum. These compounds were fairly stable under the conditions used, and the protonated molecules or fragment ions characteristic of the molecule appeared as base peaks in the mass spectra and were used for selected ion monitoring. HPLC-APCI-MS is a very promising approach for structural investigations of positional isomers and stereoisomers. This method was applied successfully to stereoisomeric Aconitum alkaloids differing in configuration at C-1, -6, or -12. Comparison of the APCI spectra showed that the abundance of fragment ions was significantly higher for the C-1, -6, or -12 β-form alkaloid than for C-1, -6, or -12 α-form alkaloid. The main alkaloid constituents in the root of A. yesoense var. macroyesoense, Aconitum alkaloids of the C20-diterpenoid type, kobusine and pseudokobusine, and their acyl derivatives were examined for their peripheral vasoactivities by measuring laser-flowmetrically the cutaneous blood flow in the hind foot of mice after intravenous administration. It is thought that the hydroxyl groups of alkaloids, especially a free OH group of pseudokobusine at C-6, were important for action on the peripheral vasculature leading to dilatation, and the results indicated that esterification of the hydroxyl group at C-15 with either anisoate, veratroate, or p-nitrobenzoate may contribute to enhancement of the activity of the parent alkaloids.
Tubular absorption and urinary secretion are important physiological functions for the maintenance of body fluid homeostasis and detoxification of drugs and xenobiotics. The proximal tubular epithelial cells play a principal role in limiting or preventing the toxicity of administered drugs by actively secreting organic cations from the circulation into the urine. Rat(r)OCT2 was identified as a second member of the organic cation transporter (OCT) family and is predominantly expressed in the kidney. In the reverse-transcriptase-polymerase chain reaction of microdissected nephron segments, rOCT1 mRNA was detected primarily in the superficial and juxtamedullary proximal convoluted tubules, whereas rOCT2 mRNA was detected widely in the superficial and juxtamedullary proximal straight tubules and some other nephron segments. The inhibitory potencies of cationic drugs and endogenous cations on the tetraethylammoniun (TEA) uptake via rOCT1 and rOCT2 indicates that rOCT1 and rOCT2 have similar affinity for many compounds, although there are moderate differences in the affinity for several compounds, such as 1-methyl-4-phenylpyridinium, dopamine, disopyramide, and chlorpheniramine. On the other hand, there were gender differences in the expression levels of rOCT2, but not of rOCT1, in rat kidneys; both mRNA and protein levels of rOCT2 in the kidneys were higher in males than females. These results suggest that rOCT1 and rOCT2 play distinct roles in the basolateral membranes of renal tubules mediating tubular secretion of cationic drugs.
Magainin 2 and tachyplesin I (T-SS) are membrane-permeabilizing antimicrobial peptides discovered in frog skin and horseshoe crab hemolymph, respectively. They are classified into different secondary structural classes, i.e., α-helix and cyclic β-sheet, respectively. We found that F5W-magainin 2 (MG2) and T-SS showed marked synergistic effects against gram-negative and -positive bacteria without enhancing hemolytic activity as a measure of toxicity. The results of dye-release experiments using liposomes suggested that the selective synergism is mainly due to anionic phospholipid-specific synergism in membrane permeabilization. Furthermore, the cyclic structure of T-SS was found to be necessary for synergism because a linear analogue of T-SS did not show good synergism with MG2. These novel observations suggest the possibility of development of cocktail therapeutic regimens using combinations of antimicrobial peptides.
Parkinson's disease (PD) is believed to be induced by the interaction of genetic predisposition and environmental factors, and a type of neurotoxin is proposed to be one of the environmental factors. We designed and synthesized a molecule, 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) as a possible PD-eliciting neurotoxin and evaluated its characteristics relevant to PD. 1BnTIQ is an endogenous amine in the brain and the 1BnTIQ content increases in the patients with PD. Repeated administration of 1BnTIQ induced PD-like symptoms in monkeys and mice. 1BnTIQ was biosynthesized from 2-phenylethylamine and phenylacetaldehyde, which is a metabolite of 2-phenylethylamine, and used in in vivo and in vitro studies. 1BnTIQ inhibited [3H]dopamine uptake in HEK293 cells which stably express dopamine transporter. 1BnTIQ also inhibited NADH-ubiquinone oxidoreductase (complex I) in the mitochondrial respiratory chain. Next, we assessed 1BnTIQ neurotoxicity in the organotypic coculture of the ventromedial portion of the mesencephalon and striatum. 1BnTIQ decreased the dopamine content in the mesencephalon in both dose-and time-dependent manners and it irreversibly reduced the dopamine content. Furthermore, it caused morphological changes in tyrosine hydroxylase-positive cells in the mesencephalon and reduced the number of cells. 1-(3′,4′-Dihydroxybenzyl)-1,2,3,4-tetrahydroisoquinoline (3′4′DHBnTIQ) is also an endogenous parkinsonism-inducing 1BnTIQ derivative. In vivo and in vitro studies revealed that 3′4′DHBnTIQ was O-methylated by soluble catechol-O-methyltransferase (COMT). The result that COMT inhibitor suppressed 3′4′DHBnTIQ neurotoxicity suggests that 3′4′DHBnTIQ is metabolically activated by COMT to exert toxic effects.
Some methods for innovative molecular transformations using optically active α-amino acids have been exploited. 1) The non-Kolbe reaction of the N-benzoyloxazoline derivative 1 derived from L-serine gave the optically active N,O-acetal 2 when graphite was used an anode material. This reaction represents the first example of “memory of chirality” in the carbenium ion chemistry. 2) The optically active pipecolic acid derivative 13, prepared from L-lysine by using electrochemical oxidation, was cyclopropanated with high diastereoselectivity (96.6%de), and the product 14 was transformed into (2S,3R)-metanopipecolic acid (7). 3) An enantiomerically pure 1,2-dihydropyridine 23 was prepared from L-lysine using electrochemical oxidation as a key step and was utilized as a chiral diene synthon in the Diels-Alder reaction. That is, in the presence of AlCl3, the Diels-Alder reaction between 23 and N-acryloyloxazolidinone 24 gave a cycloadduct with high stereoselectivity, which was converted to an optically active isoquinuclidine derivative 26 (96.8%ee). 4) The Hofmann rearrangement of the L-glutamine derivative 27 to the enantiomerically pure 2-aminobutyric acid derivative 28 was successfully achieved with an electrochemical method using a trifluoroethanol-MeCN solvent system. 5) Some types of N-formyl cyclic amine derivatives were found to be effective activators of trichlorosilane to reduce ketones and imines. Namely, the reduction of ketones and imines by trichlorosilane with a catalytic amount of L-proline derivatives 30 and 32 gave enantiomerically enriched sec-alcohols and amines, respectively, to some extent of optical yields.
Fast-disintegrating (FD) tablets containing nicorandil-loaded dry emulsions were prepared and their controlled-release properties were examined and compared with the plain FD tablets (FD tablets without dry emulsions) and commercial tablets. The dry emulsions were prepared with myristyl alcohol and stearyl alcohol and their property was modified by mixing the ratio of the two alcohols. Disintegration time of the prepared FD tablets was sufficiently fast (i.e., 12 to 23s). In vitro release of nicorandil from the FD tablets containing the dry emulsions was sustained over 6h, while that from plain FD and commercial tablets was complate within 5min. In vivo absorption of nicorandil from the tablets was evaluated by oral administration in beagle dogs. FD tablets containing dry emulsions showed a similar AUC, lower Cmax, and delayed Tmax compared to the plain FD and commercial tablets. These results suggest that the dry emulsion-loaded FD tablets can be utilized to improve the sustained-release property of active drugs.
We have confirmed that theanine, a major amino acid in green tea, enhances the antitumor activity of doxorubicin (DOX) without an increase in DOX-induced side effects. We believe that the action of theanine is due to decreases in glutamate uptake via inhibition of the glutamate transporter, intracellular glutathione (GSH) synthesis, GS-DOX conjugate level, and subsequent extracellular transport of GS-DOX by the MRP5/GS-X pump. To increase the clinical usefulness of theanine, we examined its effects on the antitumor activity of cisplatin and irinotecan (CPT-11), which a known to be transported by the efflux system related to MRP. Cisplatin decreased tumor volume in M5076 tumor-bearing mice. Furthermore, the combination of theanine with cisplatin increased the decrease in tumor volume as compared with the cisplatin-alone group. Tumor volume in the CPT-11-alone group did not show a decrease, but the combination of theanine with CPT-11 significantly reduced tumor volume. The concentration of cisplatin in the tumor was significantly increased by combination with theanine, and thus we assume that it correlated with the enhancement on the antitumor activity of theanine. On the other hand, changes in drug concentrations with theanine were not observed in normal tissues, but rather it is indicated that theanine tends to reduce their concentrations. Therefore theanine enhances the antitumor activity not only of DOX but also of cisplatin or CPT-11.
In most medical institutions, although total parenteral nutrition (TPN) should be prepared by pharmacists in sterile condition, nurses actually perform this procedure in hospital wards. The currently growing belief is that pharmacists should prepare all preparations for injection using aseptic technique. Therefore, we conducted a survey on how physicians and nurses feel about methods of preparation of TPN and other agents for injection. The results demonstrated that physicians and nurses desired pharmacists to prepare all agents for injection according to prescriptions using aseptic technique, under pharmacological control and on a 24-hours basis. Based on these results, we examined a method to realize this expectation to the extent possible in our hospital and applied it when aseptic TPN preparations were extended to include relatively stable patients requiring TPN in all hospital wards. The number of TPN preparations increased steadily. The mean number of aseptic TPN preparations after stabilization of this method was 1214 a month. A total of 48% of all TPN solutions required were prepared in aseptic condition, with an average of 4.4 vials of agents mixed per prescription. For TPN base solution, 71% of a double-bag preparation consisting of electrolytes, saccharides, and amino acids was used. It was prepared in the wards most often for the reason, “described as an unscheduled prescription”. The cost of consumables required for aseptic preparations was approximately 1.7 times the insurance coverage for addition of aseptic preparations. The physicians and nurses supported the method used by the pharmacists. To ensure complete aseptic preparation of injections by pharmacists, additional pharmacists, a review on their working system, more insurance points, and a broader range of insurance coverage may be required.