Otakar Humpa

New and facile method of preparation of the anti-HIV-1 agent,1,3-dicaffeoylquinic acid

A facile and inexpensive preparation of 1,3-dicaffeoylquinic acid (cynarin) from the leaves Cynara cardunculus L. (Asteraceae) without the use any chromatographic steps is described. The procedure was based on separation of the fraction rich in 1,5-dicaffeoylquinic acid, isomerisation of 1,5-dicaffeoylquinic acid to cynarin and, owing to its higher polarity, the simple isolation of cynarin from the reaction mixture. Cynarin inhibited HIV-1 replication in MT-2 cell culture at nontoxic concentrations similar to other previously tested dicaffeoylquinic acids, which have been recently established as a potent and highly selective class of HIV-1 integrase inhibitors.

15N NMR study of isoquinoline alkaloids

15N NMR chemical shifts of 40 tertiary and quaternary isoquinoline alkaloids of six constitutional types are reported. The selected compounds belong to the classes of benzo[c]phenanthridine, protoberberine, benzylisoquinoline, aporphine, pavinane, and β‐carboline‐proaporphine alkaloids. The 15N chemical shifts were measured by gradient‐enhanced inverse‐detected single‐quantum (GSQMBC) and multiple‐quantum (GHMBC) multiple‐bond correlation experiments. The 1H–15N long‐range coupling constants determined from the phase‐sensitive GSQMBC spectra are also reported in order to facilitate optimization of multiple‐bond correlation experiments. Copyright

Identification of key structural characteristics of Schisandra chinensis lignans involved in P-glycoprotein inhibition.

The aim of the present study was to determine the structural requirements for dibenzocyclooctadiene lignans essential for P-glycoprotein inhibition. Altogether 15 structurally related lignans isolated from Schisandra chinensis or prepared by modification of their backbone were investigated, including three pairs of enantiomers. P-Glycoprotein inhibition was quantified using a doxorubicin accumulation assay in human promyelotic leukemia HL60/MDR cells overexpressing P-glycoprotein. A preliminary quantitative structure-activity relationship analysis revealed three main structural features involved in P-glycoprotein inhibition: a 1,2,3-trimethoxy moiety, a 6-acyloxy group, and the absence of a 7-hydroxy group. The most effective inhibitors, (-)-gomisin N (1) and (+)-deoxyschizandrin [(+)-2], were selected for further evaluation of their effects. Both these lignans restored the cytotoxic effect of doxorubicin in HL60/MDR cells and when combined with a subtoxic concentration of this compound increased the proportion of G2/M cells significantly, which is a usual response to treatment with this anticancer drug.

1H‐, 13C‐, and 15N‐NMR chemical shifts for selected glucosides and ribosides of aromatic cytokinins

The 1H and 13C NMR resonances of 16 purine glucosides were assigned by a combination of one‐ and two‐dimensional NMR experiments, including gs‐COSY, gs‐HSQC, and gs‐HMBC, in order to characterize the effect of substituent and the position of glucose unit on the NMR chemical shifts. In addition, 15N NMR chemical shifts for selected derivatives were investigated by using 1H15N chemical shift correlation techniques. To map the influence of sugar moiety on the directly bonded nitrogen atom, selected N9‐glucosides and their ribose analogs were compared. Characteristic long‐range 1H15N coupling constants, measured by using 1H15N gradient‐selected single‐quantum multiple bond correlation (GSQMBC), are also reported and discussed. All compounds investigated here belong to cytokinins, an important group of plant hormones. Copyright

Validated method for bioactive lignans in Schisandra chinensis in vitro cultures using a solid phase extraction and a monolithic column application.

A simple and rapid method for determination of six lignans found in plant cell cultures of Schisandra chinensis was developed and validated. The lignans were extracted from plant samples with methanol and the extracts were effectively cleaned by solid-phase extraction using Strata C18-E (Phenomenex) cartridges. Chromatographic separation was carried out on a Chromolith Performance RP-18e monolithic column (100 x 4.6 mm, Merck) using an isocratic mobile phase of acetonitrile and water in a 50:50 (v/v) ratio. The eluent was monitored at 220 nm. The baseline separation of schizandrin, gomisin A, deoxyschizandrin, gamma-schizandrin, gomisin N and wuweizisu C was achieved in a relatively short time period (20 min), which was made possible by the relatively high flow rate of the mobile phase (2 mL/min). The lower limit of quantitation was 0.1 mg/L for schizandrin and gomisin A, 0.3 mg/L for deoxyschizandrin, gamma-schizandrin, and gomisin N and 1 mg/L for wuweizisu C. The analysis of spiked samples containing six lignans provided absolute recoveries between 93 and 101% in all cases. The validated method was successfully applied to the determination of lignans in embryogenic plant cell cultures of Schisandra chinensis.

Acid-Base Initiated Cyclization and Retrocyclization Reactions of Ethyl 2-(3-Acylselenoureido)benzoates, -thiophene-3-carboxylates and the Corresponding 2-(3-Acylisoselenoureido) Derivatives

Acid and base initiated cyclization and retrocyclization reactions of the selenoureas 1-6 and isoselenoureas 7-12 to fused 4H-1,3-selenazine and 1,2,3,4-tetrahydropyrimidine-4-one skeletons are reported. Fused 2-acylamino-4H-1,3-selenazine-4-ones 13-18 were formed by the action of concentrated sulfuric acid on acylselenoureas 1-6 or on 2,2-dimethylpropanoylisoselenoureas 10-12 at room temperature. On the other hand, benzoylisoselenoureas 7-9 were not obtained in this cyclocondensation under the same conditions. The reaction of potassium ethoxide on selenazines 13-18 in the ethanol solution evoked retrocyclization to the starting acylselenoureas 1-6. Both types of the title compounds, i.e. selenoureas 1-6 and isoselenoureas 7-12, were deprotonated in a methanol solution of potassium hydroxide used in an equimolar amount, giving rise to potassium salts 19-24, which were isolated only for the thiophene series. By heating the separated potassium salts 20, 21, 23 and 24 in the methanol solution provided, deacylation and isoselenoureas 26, 27 were formed. The in situ prepared salts 19, 22 cyclized under the same conditions with deacylation to 4-selanyl-3,4-dihydroquinazoline-4-one 28. The title compounds 1-6, 7-12 and products of their deacylation 26, 27 on boiling in methanolic potassium hydroxide cyclized to the corresponding fused 2-selenoxo-1,2,3,4-tetrahydropyrimidine-4-one potassium salts. These compounds provided pyrimidine-4-ones 28-30 on acidification. Acid initiated retrocyclization 28-30 to the corresponding 2-amino-4H-1,3-selenazine-4-ones was unsuccessful. C, H, N, Se elemental analyses, FTIR, 1H-NMR, and 13C-NMR spectroscopies supported the structure of synthesized compounds.A short review on cardiotonic steroids and their analogues is presented. The natural, semisynthetic and synthetic derivatives, as well as their mechanism of action and structure-activity relationships are shown, with a special reference to aminoguanidine derivatives.

A Simple and Expeditious Synthesisof Substituted 3-Aminoindolizines

Summary. Treatment of easily available 2-formyl-1,4-dihydropyridines with 3-oxo-3-phenylpropanenitrile offers a simple and efficient one-pot method for the preparation of substituted 3-aminoindolizines.Zusammenfassung. Die Umsetzung der einfach zugänglichen 2-Formyl-1,4-dihydropyridine mit 3-Oxo-3-phenylpropannitrilen stellt eine einfache und effiziente Eintopfmethode zur Darstellung substituierter 3-Aminoindolizine dar.

Synthesis and Characterization of New 3-(4-Arylpiperazin-1-yl)-2-hydroxypropyl 4-Propoxybenzoates and Their Hydrochloride Salts

Five new 3-(4-arylpiperazin-1-yl)-2-hydroxypropyl 4-propoxybenzoates were designed and synthesized as potential dual antihypertensive agents. The compounds were prepared as free bases and subsequently transformed to hydrochloride salts. The position of protonation of nitrogen atoms in the piperazine ring of hydrochloride salts was determined by means of 13C-CP/MAS and 15N-CP/MAS NMR and IR spectroscopy. Using these solid-state analytical techniques, it was found that both nitrogen atoms were protonated when excess hydrogen chloride was used for preparation of salts. On the other hand, when the equimolar amount of hydrogen chloride was used, piperazine nitrogen substituted by aryl was protonated.

New P–S–N containing ring systems. Reaction of 2,4-(naphthalene-1,8-diyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide with methylbis(trimethylsilyl)amine

From the reaction of 2,4-(naphthalene-1,8-diyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide 1 with methylbis(trimethylsilyl)amine 2 in dichloromethane a product of the P2S2 ring cleavage, (C10H6)P(S)(SSiMe3)(µ-S)P(S)(NMeSiMe3) 3, was isolated, existing in an equilibrium between two diastereomeric forms in solution. Compound 3 was also obtained when toluene was used as a solvent. Its subsequent reaction with pyridine (py) led to the desilylated ionic product [Hpy+][(C10H6)P(S)(NHMe)(µ-S)PS2–] 4, which reacts with tetraphenylphosphonium chloride to give [PPh4+][(C10H6)P(S)(NHMe)(µ-S)PS2–] 5. When acetonitrile was used as a solvent a cage compound 2,6-(naphthalene-1,8-diyl)-3,4-dimethyl-1,3,5,2λ5,6λ5-thiadiazadiphosphinine 2,6-disulfide 6 containing a six-membered CN2P2S heterocycle was obtained. The new compounds were studied spectroscopically (1- and 2-D high resolution NMR, IR, MS) and in the cases of 3, 5 and 6 by X-ray crystallography.

β-Hydroxynaphthoic acid synthesis monitoring by capillary zone electrophoresis and high-performance liquid chromatography: Determination of polynaphthyl derivatives

Abstract Unidentified peaks were observed during the purity control of β-hydroxynaphthoic acid industrial samples using capillary zone electrophoresis (CZE) and HPLC methods. The origin of such peaks was supposed to be (1) a consequence of interaction between separated compounds and borate species, which might cause peak splitting, or (2) other side-products formed during the synthesis, such as polynaphthyl derivatives of β-hydroxynaphthoic acid and/or others. Both hypotheses were studied using CZE, HPLC, and TLC methods. The synthesis of 2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylic acid was done. The purified compound was use as standard to identify the unknown impurities in β-hydroxynaphthoic acid samples. To control the quality of the standard, NMR, HPLC and CZE were applied. It has been proved that the unidentified impurities were other sub-products from the synthesis and the formation of 2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylic acid was verified.