Progress on the Synthesis of the Aromathecin Family of Compounds: An Overview.

We present a systematic review of the methods developed for the synthesis of the aromathecin family of compounds (benz[6,7]indolizino[1,2-b]quinolin-11(13H)-ones) and their derivatives. These methods can be broadly classified into four categories based on the construction of pentacyclic structures: Category 1: by constructing a pyridone moiety (D-ring) on the pyrroloquinoline ring (A/B/C-ring), Category 2: by constructing a pyridine moiety (B-ring) on the pyrroloisoquinolone ring (C/D/E-ring), Category 3: by constructing an indolizidinone moiety (C/D-ring) in a tandem reaction, and Category 4: by constructing a pyrrolidine moiety (C-ring) on the isoquinolone ring (D/E-ring).

A Novel Amphotericin B Hydrogel Composed of Poly(Vinyl Alcohol)/Borate Complex for Ophthalmic Formulation.

In this study, we developed a water-soluble complex-hydrogel viscosity-controlled formulation of amphotericin B (AmB). AmB is insoluble in water, but borax makes it soluble by forming a complex with AmB. Borax also forms complexes with poly(vinyl alcohol) (PVA) to produce viscous hydrogels. Furthermore, boric acid interacts with mucin expressed in corneal epithelial cells. Accordingly, by utilizing these properties of borax simultaneously, we prepared a water-soluble AmB complex-hydrogel with poly(vinyl alcohol)/borate (PVA-B-AmB), which is suitable for eye drops. PVA-B-AmB was easily prepared by simply mixing aqueous AmB solution dissolved in borax, PVA solution, and water. The 11B-NMR results suggested that PVA-B-AmB existed by bonding PVA and AmB via boronic acid. PVA-B-AmB (gel ratio = 0.55) has a viscosity of 18.3 ± 0.5 mPa·s and is suitable for ophthalmic formulations. This formulation exhibited sustained release of AmB of approximately 45% at 24 h. It was also shown that this formulation interacts with mucin. These results suggest that PVA-B-AmB can be used as a water-soluble AmB preparation suitable for ophthalmic use.

Effects of Carbazole Derivatives on Neurite Outgrowth and Hydrogen Peroxide-Induced Cytotoxicity in Neuro2a Cells.

Many studies have demonstrated that oxidative stress plays an important role in several ailments including neurodegenerative diseases and cerebral ischemic injury. Previously we synthesized some carbazole compounds that have anti-oxidant ability in vitro. In this present study, we found that one of these 22 carbazole compounds, compound 13 (3-ethoxy-1-hydroxy-8- methoxy-2-methylcarbazole-5-carbaldehyde), had the ability to protect neuro2a cells from hydrogen peroxide-induced cell death. It is well known that neurite loss is one of the cardinal features of neuronal injury. Our present study revealed that compound 13 had the ability to induce neurite outgrowth through the PI3K/Akt signaling pathway in neuro2a cells. These findings suggest that compound 13 might exert a neurotrophic effect and thus be a useful therapy for the treatment of brain injury.

Antioxidant effects of the highly-substituted carbazole alkaloids and their related carbazoles.

Antioxidant activities of 3-oxygenated and 3,4-dioxygenated carbazole alkaloids and their related carbazoles were comprehensively evaluated. In all assay systems, the 3,8-dihydroxycarbazoles carbazomadurin A (2) and B (3), and their synthetic precursors 2a and 3a exhibited higher antioxidant activities than the 3-monohydroxycarbazoles carazostatin (1), and the synthetic precursors 4a and 4b of carquinostatin A (4). In particular, 2a and 3a exhibited strong scavenging activities due to the reducing ability of formyl group at the C-5 position of carbazoles. The results suggest that these compounds could serve as useful clues for designing and developing novel antioxidants.

Simple enrichment of thiol-containing biomolecules by using zinc(II)-cyclen-functionalized magnetic beads.

A simple and efficient method based on magnetic-bead technology has been developed for the enrichment of thiol-containing biomolecules, such as l-glutathione and cysteine-containing peptides. The thiol-binding site on the bead is a mononuclear complex of zinc(II) with 1,4,7,10-tetraazacyclododecane (cyclen); this is linked to a hydrophilic cross-linked agarose coating on a particle that has a magnetic core. All steps for the thiol-affinity separation are conducted in aqueous buffers with 0.10 mL of the magnetic beads in a 1.5 mL microtube. The entire separation protocol for thiol-containing compounds, from addition to elution, requires less than one hour per sample, provided the buffers and the zinc(II)-cyclen-functionalized magnetic beads have been prepared in advance. The thiol-affinity magnetic beads are reusable at least 15 times without a decrease in their thiol-binding ability, and they are stable for six months at room temperature.

Development and Evaluation of EDTA-Treated Rabbits for Bioavailability Study of Chelating Drugs Using Levofloxacin, Ciprofloxacin, Hemiacetal Ester Prodrugs, and Tetracycline.

Laboratory rabbits are fed foods rich with cationic metals, and while fasting cannot empty gastric contents because of their coprophagic habits. This implies that, in rabbits, the oral bioavailability of chelating drugs could be modulated by the slow gastric emptying rates and the interaction (chelation, adsorption) with gastric metals. In the present study, we tried to develop a rabbit model with low amounts of cationic metals in the stomach for preclinical oral bioavailability studies of chelating drugs. The elimination of gastric metals was achieved by preventing food intake and coprophagy and administering a low concentration of EDTA 2Na solution one day before experiments. Control rabbits were fasted but coprophagy was not prevented. The efficacy of rabbits treated with EDTA 2Na was evaluated by comparing the gastric contents, gastric metal contents and gastric pH between EDTA-treated and control rabbits. The treatment with more than 10 mL of 1 mg/mL EDTA 2Na solution decreased the amounts of gastric contents, cationic metals and gastric pH, without causing mucosal damage. The absolute oral bioavailabilities (mean values) of levofloxacin (LFX), ciprofloxacin (CFX) and tetracycline hydrochloride (TC), chelating antibiotics, were significantly higher in EDTA-treated rabbits than those in control rabbits as follows: 119.0 vs. 87.2%, 9.37 vs. 13.7%, and 4.90 vs. 2.59%, respectively. The oral bioavailabilities of these drugs were significantly decreased when Al(OH)3 was administered concomitantly in both control and EDTA-treated rabbits. In contrast, the absolute oral bioavailabilities of ethoxycarbonyl 1-ethyl hemiacetal ester (EHE) prodrugs of LFX and CFX (LFX-EHE, CFX-EHE), which are non-chelating prodrugs at least in in vitro condition, were comparable between control and EDTA-treated rabbits irrespective of the presence of Al(OH)3, although some variation was observed among rabbits. The oral bioavailabilities of LFX and CFX from their EHE prodrugs were comparable with LFX and CFX alone, respectively, even in the presence of Al(OH)3. In conclusion, LFX, CFX and TC exhibited higher oral bioavailabilities in EDTA-treated rabbits than in control rabbits, indicating that the oral bioavailabilities of these chelating drugs are reduced in untreated rabbits. In conclusion, EDTA-treated rabbits were found to exhibit low gastric contents including metals and low gastric pH, without causing mucosal damage. Ester prodrug of CFX was effective in preventing chelate formation with Al(OH)3 in vitro and in vivo, as well as in the case of ester prodrugs of LFX. EDTA-treated rabbits are expected to provide great advantages in preclinical oral bioavailability studies of various drugs and dosage formulations. However, a marked interspecies difference was still observed in the oral bioavailability of CFX and TC between EDTA-treated rabbits and humans, possibly due to the contribution of adsorptive interaction in rabbits. Further study is necessary to seek out the usefulness of the EDTA-treated rabbit with less gastric contents and metals as an experimental animal.

Total synthesis of (±)-carquinostatin a, and asymmetric total synthesis of (R)-(-)-carquinostatin a and (s)-(+)-carquinostatin a.

Total syntheses of (±)-carquinostatin A (1), and (R)-(-)-carquinostatin A (1a) together with its enantiomer, (S)-(+)-carquinostatin A (1b), possessing radical scavenging activity, were newly achieved. (±)-Carquinostatin A (1) was synthesized from 1-acetonyl-6-bromo-3-ethoxy-2-methylcarbazole (6), which was derived from the known 1-acetonyl-3-ethoxy-2-methylcarbazole (5). Introduction of a prenyl group at the 6-position of carbazole was successful in two steps. For the synthesis of (R)-(-)-carquinostatin A (1a) and (S)-(+)-carquinostatin A (1b), (R)-(-)-1-(2-acetoxypropyl)-3-hydroxy-2-methylcarbazole (15a) and (S)-(+)-3-hydroxy-1-(2-hydroxypropyl)-2-methylcarbazole (15b), prepared by lipase-QLM catalyzed enantioselective transesterification of 3-hydroxy-1-(2-hydroxypropyl)-2-methylcarbazole (14), were used as the chiral starting material.

Total Syntheses of Multi-substituted Carbazole Alkaloids and Phenolic Related Compounds, and Evaluation of Their Antioxidant Activities.

This review describes the syntheses and antioxidant activities of carbazole alkaloids carquinostatin A, carbazomadurin A and carbazomadurin B and their related carbazoles. The key step was an allene-mediated electrocyclic reaction involving an indole [b]-bond for the construction of a highly substituted carbazole ring. Antioxidant activities of 3-oxygenated and 3,4-dioxygenated carbazole alkaloids and their related carbazoles were comprehensively evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS)+ radical scavenging assays, and cupper reducing power. Furthemore, the antioxidant activities of simple phenolic carbazoles were evaluated by DPPH and ABTS+ radical scavenging assays. After this, bond dissociation energies (BDE) and highest occupied molecule orbital energy levels (EHOMO) of a series of phenolic carbazoles, including phenolic carbazole alkaloids, were also calculated and then examined for correlation with their antioxidant activities. The phenolic carbazole core possessing a hydroxyl group at the 1-, 3-, 6-, or 8-positions could play an important role in the antioxidant activity of carbazole alkaloids. The results suggest that these compounds could serve as useful clues for designing and developing novel antioxidants.

A novel thiol-affinity micropipette tip method using zinc(II)-cyclen-attached agarose beads for enrichment of cysteine-containing molecules.

Cysteine-containing biomolecules are attractive targets in the study of thiol biology. Here we introduce a novel method for the selective enrichment of thiol-containing molecules using a thiol-capture zinc(II) complex of 1,4,7,10-tetraazacyclododecane (Zn(2+)-cyclen). Recognition of N-acetylcysteine amide by Zn(2+)-cyclen has been studied by potentiometric pH titration, revealing formation of a 1:1 thiolate-bound Zn(2+)-cyclen complex with a large thiolate-affinity constant of 10(6.2)M(-1) at 25°C and I=0.10M (NaCl). The Zn(2+)-bound thiolate anion is unexpectedly stable in aqueous solution at pH 7.8 under atmospheric conditions for a few days. These findings have contributed to the development of a convenient method for separation of thiol compounds by using a micropipette tip. A 200µL micropipette tip containing 10µL of hydrophilic cross-linked agarose beads attached to Zn(2+)-cyclen moieties was prepared. All steps for thiol-affinity separation (binding, washing, and eluting) are conducted using aqueous buffers at room temperature. The entire separation protocol requires less than 15min per sample. We demonstrate practical example separations of cysteine-containing molecules. This micropipette tip method would be used preferentially as an alternative to existing tools for reliable enrichment of thiol-containing molecules.

[Increase in lipophilicity of enalaprilat by complexation with copper(II) or zinc(II) Ions].

Enalaprilat (H2L), which is the active metabolite of the pro-drug enalapril, is an angiotensin-converting enzyme inhibitor. Some side effects such as neurodegeneration and taste disorder can be related to copper or zinc deficiency, which would be caused by the metal complex formation of dianionic elalaprilat (L(2-)). For a better understanding of this phenomenon, we investigated the solution species of enalaprilat in the presence of copper(II) or zinc(II) ions by pH titration analysis with I=0.10 M (NaCl) at 25℃. The 1:1 complex formation constants (KML=[ML]/[M(2+)][L(2-)] M(-1)) of 10(7.4) for CuL and 10(4.4) for ZnL complexes were evaluated, indicating the presence of those complexes at a physiological pH. Furthermore, partition experiments with a two-phase system of 1-butanol/water at 25℃ disclosed that copper(II) and zinc(II) complexes of enalaprilat were partially extracted into the organic layer. In the absence of those metal ions, enalaprilat was not soluble in the 1-butanol phase. The increase in lipophilicity of enalaprilat by metal complexation suggests that the long-term administration of enalapril could be a possible risk factor for the disrupted distribution of those metal ions in biological systems.