Synthetic investigation on physiologically active natural products having picrotoxinin type (picrotoxane) sesquiterpenoids and terpene alkaloids is reviewed. Terpene alkaloid, dendrobine has been synthesized successfully by four groups in a racemic form. From a synthetic standpoint, the more challenging and complex target was the sesquiterpenoid of this class and total syntheses of picrotoxinin, coriamyrtin and tutin have been accomplished in these five years. Of these synthetic works picrotoxinin has been synthesized from (-)-carvone in twenty steps and coriamyrtin from protoanemonin in fifteen steps utilizing the efficient, beautiful and stereocontrolled synthetic strategies. Total syntheses of these terpenoids have been also achieved by using isotwistane compound as a common intermediate. Synthetic approach to the above natural products is also briefly described.
For the purpose of the development of modern procedures of glycoside-chemistry, a number of anomeric pairs of D-glucopyranosides, D-mannopyranosides, L-rhamnopyranosides and L-arabinopyranosides of a variety of aliphatic alcohols and carboxylic acids were synthesized. For these glycosides together with the known natural glycosides, carbon signal displacements of both aglycone- and sugar-moieties on glycoside formation, "glycosylation shift" were studied. The exceptional glycosylation shifts for glycosides of relatively hindered aglycone alcohols and carboxylic acids as well as 2-linked glycosides were discussed under the stereochemical consideration. It was also revealed that 13C-nuclear magnetic resonance spectrometry is a valuable tool for the determination of anomeric configuration of mannosides and rhamnosides. In the application of these results, structures of a number of dammarane-saponins of Ginseng and the related Panax species, natural sweet glycosides and glycoside of oriental medicinal plants have been elucidated.
The structure of surugatoxin (1) is characterized by a highly functionalized spirooxindole moiety fused to a tetrahydropteridine ring. To establish a method for the construction of this unique ring system, the synthesis of 5'-ethoxycarbonyl-3'-hydroxy-3'-methyl-2-oxoindoline-3-spiro-4'-piperidine-2'-one (5) was first examined as a model compound corresponding to the spiro-oxindole moiety of 1. The procedure described in this paper involves the preparation of the spiro-oxindole 5 from ethyl 3-amino-2-(2-oxo-3-indolinyl) propionate hydrochloride (3) by acylation with 2-methoxyacrylic acid-dicyclohexylcarbodiimide followed by acidic hydrolysis (1% HCl-EtOH) and subsequent ring closure of the resulting pyruvoyl amide 4 to 5a-d as a separable mixture of four stereoisomers under basic conditions [tris buffer (pH 8.0)-EtOH or NH4OH-EtOH].
6-Bromoisatin, prepared from 2-nitroaniline in 7 steps, was condensed with ethyl 4-phthalimidoacetoacetate (10) under Knoevenagel conditions to give ethyl 2-(6-bromo-2-oxo-3-indolinylidene)-3-oxo-4-phthalimidobutyrate (11) in 83% yield. Reduction of 11 with sodium hydrosulfite in boiling EtOH afforded an enolized diastereomeric mixture of the oxindole derivative 12 (90%). Careful treatment of 12 with hydrazine hydrate followed by hydrolysis (10% HCl) gave amino-ketone hydrochloride 13 (49%).
2, 4-Dibenzyloxy-6-ethylsulfonyl-5-nitropyrimidine (8) corresponding to the 5, 6-disubstituted uracil moiety in surugatoxin was prepared from 6-chloro-5-nitrouracil (3) in 50% overall yield by the following 4 steps : 1) EtSNa, 2) POCl3, 3) PhCH2ONa, and 4) mchloroperbenzoic acid. Coupling of 8 with the amino-ketone 2 in N, N-dimethylformamide at room temperature in the presence of an excess amount of NaHCO3 yielded the nitro-ketone 16 in 92% yield.
Unexpected results in the initial experiments for the construction of the pentacyclic surugatoxin framework from debromo-nitro-ketone 9 are described in this paper. Treatment of 9 with pyruvoyl chloride in pyridine gave nitro-enol lactone 10 which was reduced with Zn/AcOH to give amino-enol lactone 11. When a solution of 11 in CH2Cl2 was kept at room temperature, 11 was gradually decomposed to tetrahydropteridine 13. On the other hand, 9 was transformed to amide 16 by the sequence 1) conversion to methoxymethyl enol ether 14 by the treatment with K2CO3 in N, N-dimethylformamide and subsequent reaction with chloromethyl methyl ether, 2) reduction of the nitro group to amine 15 (Zn/AcOH), and 3) acylation of 15 with 2-methoxyacrylic acid-dicyclohexylcarbodiimide. When 16 was treated with 20% trifluoroacetic acid in CH2Cl2, unexpected ring closure occurred to form tetrahydropteridine 18.
The dehydrated surugatoxin framework was constructed by the following reactions. Oxidative acetylation of tetrahydropteridine 2 with Ac2O-pyridine to dihydropteridinediacetate 5, followed by reduction (NaBH3CN), gave a isatinylidene derivative 8. Acylation of 8 with pyruvoyl chloride in benzene gave pyruvoyl amide 9. Heating 9 in pyridine at 50°C resulted in a stereospecific ring closure to afford ethyl ester analogue 10 of dehydrated surugatoxin.
Dehydrated surugatoxin ethyl ester analogue 14 was prepared from bromo-nitroketone 11. Alkaline hydrolysis [2% MeONa-MeOH, tetrahydrofuran (THF), room temperature] of 14 gave an enamine derivative 15 which was treated with OsO4 in THF to give a mixture of cis-diols 16α and 16β. Selective reduction of 16α with borane-pyridine complex in AcOH followed by debenzylation of the resulting monool 17 with 90% trifluoroacetic acid at 50°C for 15 min afforded a desired surugatoxin derivative 18. The structure and stereochemistry of 18 was unequivocally determined in a single crystal X-ray diffraction analysis.
Four stereoisomeric ethyl esters 6a-d of the debromo-aglycone of surugatoxin (1) were synthesized. Individual treatment of the cis-diols 4β and 4α with borane-pyridine complex in AcOH followed by hydrogenolysis (H2/Pd-C) of the resulting monools 5c and 5d gave isomeric surugatoxin analogues 6c and 6d, respectively. Heating 5d (or 5c) in 90% trifluoroacetic acid at 60°C for 6 h resulted in the formation of an equilibrium mixture of desired natural surugatoxin analogue 6a (30%) and its C4-epimer 6b (3%) together with a 3, 4-dehydrated derivative 7 (50%). However, the equilibrium was unfavorable for the natural isomer 6a, the yield of which was raised up to 65% by recycling the recovered dehydrated derivative 7 and 6b.
Release of fibrinopeptide A (FPA) from human fibrinogen by batroxobin and human thrombin was examined. The rate was measured by means of radio-immunoassay. The following results were obtained. 1. Michaelis-Menten parameters for the interaction between the enzymes and fibrinogen at pH 7.4, 37°C were determined : Batroxobin, Vmax=3.7nmol FPA/min/BU, Km=0.125μM : thrombin, Vmax=83nmol FPA/min/NIH unit, Km=3.0μM. 2. The pH-dependence of the reaction of thrombin at 4.7μM fibrinogen concentration gave a bell-shaped curve with a maximum at pH 8.5, while a sigmoid curve with flat region over pH 9 was obtained for batroxobin. The dependence of batroxobin at 0.19μM fibrinogen concentration gave a bell-shaped curve with a maximum at pH 8.5. 3. Thrombin was inhibited by diisopropyl fluorophosphate (DFP), N2-p-tosyl-L-lysine chloromethyl ketone (TLCK), benzamidine, and hirudin, and not inhibited by Trasylol. Batroxobin was inhibited by DFP, and not inhibited by TLCK, benzamidine, hirudin and Trasylol. 4. The rates of batroxobin-catalyzed release of FPA in the plasma and in purified fibrinogen solution were almost identical during 4 h incubation at 37°C. On the other hand, the thrombin-catalyzed release was inhibited in the plasma.
The measurement of extra-weak chemiluminescence of 139 kinds of tablets and capsules was carried out by use of a newly devised single photoelectron counting apparatus. The tablets and capsules tested showed chemiluminescence values of 0 to 1 380 counts/10 s, 0 to 10800 counts/10s and 37 to 245000 counts/10s, at 20, 50 and 80°C, respectively. Among the drugs tested in this report, imipramine, indole, and phenothiazine derivatives showed high chemiluminescence values.
Radiosensitizing effect of pepleomycin (PEP), an antitumor drug derived from bleomycin, was examined in mouse. PEP was intraperitoneally injected into ICR male mice. Mice irradiated with 70kVp of soft X-ray were observed for 30d. By comparing the mice survival time of the control group with that of PEP-treated group, radiosensitizing effect of PEP was detected as a shortening of the survival time. The enhancement ratio (ER) calculated by mice survival time was 1.29. PEP was most effective when injected 1 h before the irradiation, and the effect was dose dependently inhibited by a radioprotector, cysteamine (MEA).
Three new p-coumaroyl glycosides, named osmanthuside A (I), B (II) and C (III), were isolated from the leaves of Osmanthus fragrans LOUR. var. aurantiacus MAKINO. The structures of I, II and III were elucidated to be β-(p-hydroxyphenyl) ethyl 4-O-trans-p-coumaroyl-β-D-glucopyranoside, β-(p-hydroxyphenyl) ethyl O-α-L-rhamnopyranosyl-(1→3)-4-O-trans-p-coumaroyl-β-D-glucopyranoside and β-(p-hydroxyphenyl) ethyl 4-O-cis-p-coumaroyl-β-D-glucopyranoside on the basis of analyses of the nuclear magnetic resonance spectra and the circular dichroism spectra.