Two antimycin A analogues from marine-derived actinomycete Streptomyces lusitanus.

Two new antimycin A analogues, antimycin B1 and B2 (1-2), were isolated from a spent broth of a marine-derived bacterium, Streptomyces lusitanus. The structures of 1 and 2 were established on the basis of spectroscopic analyses and chemical methods. The isolated compounds were tested for their anti-bacterial potency. Compound 1 was found to be inactive against the bacteria Bacillus subtilis, Staphyloccocus aureus, and Loktanella hongkongensis. Compound 2 showed antibacterial activities against S. aureus and L. hongkongensis with MIC values of 32.0 and 8.0 µg/mL, respectively.

Metabolism of intravenous methylnaltrexone in mice, rats, dogs, and humans.

Methylnaltrexone (MNTX), a selective mu-opioid receptor antagonist, functions as a peripherally acting receptor antagonist in tissues of the gastrointestinal tract. This report describes the metabolic fate of [(3)H]MNTX or [(14)C]MNTX bromide in mice, rats, dogs, and humans after intravenous administration. Separation and identification of plasma and urinary MNTX metabolites was achieved by high-performance liquid chromatography-radioactivity detection and liquid chromatography/mass spectrometry. The structures of the most abundant human metabolites were confirmed by chemical synthesis and NMR spectroscopic analysis. Analysis of radioactivity in plasma and urine showed that MNTX underwent two major pathways of metabolism in humans: sulfation of the phenolic group to MNTX-3-sulfate (M2) and reduction of the carbonyl group to two epimeric alcohols, methyl-6alpha-naltrexol (M4) and methyl-6beta-naltrexol (M5). Neither naltrexone nor its metabolite 6beta-naltrexol were detected in human plasma after administration of MNTX, confirming an earlier observation that N-demethylation was not a metabolic pathway of MNTX in humans. The urinary metabolite profiles in humans were consistent with plasma profiles. In mice, the circulating and urinary metabolites included M5, MNTX-3-glucuronide (M9), 2-hydroxy-3-O-methyl MNTX (M6), and its glucuronide (M10). M2, M5, M6, and M9 were observed in rats. Dogs produced only one metabolite, M9. In conclusion, MNTX was not extensively metabolized in humans. Conversion to methyl-6-naltrexol isomers (M4 and M5) and M2 were the primary pathways of metabolism in humans. MNTX was metabolized to a higher extent in mice than in rats, dogs, and humans. Glucuronidation was a major metabolic pathway in mice, rats, and dogs, but not in humans. Overall, the data suggested species differences in the metabolism of MNTX.

Suitability of tetrahydofuran as a dopant and the comparison to other existing dopants in dopant-assisted atmospheric pressure photoionization mass spectrometry in support of drug discovery.

In this paper, we investigated the suitability of tetrahydofuran (THF) as a dopant and compared it against other common dopants for atmospheric pressure photoionization mass spectrometry (APPI-MS). In a systematic analysis of 37 drug standards and 100 Wyeth proprietary drug candidates, THF was found to increase ionization efficiency as high as 33-fold when introduced through a syringe pump at a flow rate of 20 microL/min, and as high as 114-fold when introduced through the mobile phase at 100 microL/min. As a dopant, THF is as effective as acetone, better than anisole, and slightly less effective than toluene for the majority of the test compounds. The increase in ionization efficiency by THF was found to be compound-dependent. THF was more effective in facilitating the ionization of polar compounds than of non-polar compounds. With THF, toluene and acetone as dopants, a single type of molecular ion ([M+H](+) or M(+*)) is produced for analyte molecules. However, anisole can cause the formation of an ion cluster for polar analytes. The cluster contains [M-2H+H](+), M(+*), and [M+H](+) ions with varied ratios. This complexity may make interpretation of spectra difficult for unknown compounds when complimentary data are not available. Our findings indicate that THF is a suitable dopant in the daily usage for increasing ionization efficiency, especially when THF is used as the mobile phase or as an organic modifier in the mobile phase.

Discovery of a new series of monoamine reuptake inhibitors, the 1-amino-3-(1H-indol-1-yl)-3-phenylpropan-2-ols.

A novel series of monoamine reuptake inhibitors, the 1-amino-3-(1H-indol-1-yl)-3-phenylpropan-2-ols, have been discovered by combining virtual and focused screening efforts with design techniques. Synthesis of the two diastereomeric isomers of the molecule followed by chiral resolution of each enantiomer revealed the (2R,3S)-isomer to be a potent norepinephrine reuptake inhibitor (IC(50)=28 nM) with excellent selectivity over the dopamine transporter and 13-fold selectivity over the serotonin transporter.

Normal-phase automated mass-directed HPLC purification of a pyrrolobenzodiazepine library with vasopressin agonist activity.

A 23-member library of pyrrolobenzodiazepine derivatives with vasopressin agonist activity was purified on a 100-mg per injection scale using normal-phase (NP) automated mass-directed HPLC. Analytical NP APCI-LC/MS on an experimental monolith silica CN column utilizing gradients of methanol in ethoxynonafluorobutane (hexane-like solvent) was used to provide data on chromatographic purity and ionization of the solutes. The analytical data collected were used to program a preparative LC/MS instrument for "smart" fraction collection based on the protonated molecular ion of the component of interest. Preparative HPLC was carried out on a preparative cyano column with gradients of polar organic solvents in heptane containing n-propylamine as a basic additive. Flow rates twice as high as conventional ones were used for purification of library compounds. Small aliquots of the preparative flow were mixed with makeup solvent and introduced into an APCI source of a quadrupole mass spectrometer, which triggered collection of solutes. Two methods with fixed instrument parameters were used for purification. The system utilized commercially available instrumentation and software, which provided excellent recovery and purity of the library components and appeared to be useful as a fast and efficient alternative to traditional purification technologies based on reversed-phase LC/MS.

Unexpected rearrangement of enantiomerically pure 3-aminoquinuclidine as a simple way of preparing diastereomeric octahydropyrrolo[2,3-c]pyridine derivatives.

Reaction of (S)- or (R)-3-aminoquinuclidine with 2-chloropyrimidine or 2-bromopyrimidine led to an unexpected formation of both cis- and trans-octahydropyrrolo [2,3]pyridine derivatives. A single-step synthesis of two of the four stereoisomers of these octahydropyrrolo[2,3]pyridine derivatives provides a convenient way of generating stereochemically defined isomers. Optimization of reaction conditions was carried out by (1)H NMR monitoring. The relative and absolute stereochemistry of all four stereoisomers was determined by a combination of (1)H, (13)C, and (15)N NMR spectroscopy and vibrational circular dichroism spectroscopy.

Integrity profiling of high throughput screening hits using LC-MS and related techniques.

Integrity profiling of HTS hits is valuable for verification of the hit identity and purity. This provides early discovery researchers with more confident SAR theories. Methodology for integrity profiling of HTS hits must be high throughput, consume little material, and selectively provide structure-based data. Analytical techniques that can be utilized for integrity profiling methods are reviewed for their appropriateness in sample preparation, component separation, detection, purity quantitation, identity confirmation, and follow-up.

Enhanced chromatographic resolution of amine enantiomers as carbobenzyloxy derivatives in high-performance liquid chromatography and supercritical fluid chromatography.

The carbobenzyloxy (cbz) protecting group is evaluated for it's potential to enhance the resolution of chiral amine enantiomers using high-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC). A series of cbz derivatives of commercially available racemates was prepared and analyzed by enantioselective chromatography using a variety of mobile phases and polysaccharide and Pirkle-type chiral stationary phases (CSPs). The cbz-derivatized product consistently demonstrated enhanced chiral resolution under HPLC and SFC conditions. Improved selectivity and resolution combined with an automated preparative HPLC or SFC system can lead to the rapid generation of highly purified enantiomers of desirable starting materials, intermediates or final products.

Optimization of a higher throughput microsomal stability screening assay for profiling drug discovery candidates.

Metabolic stability plays an important role in the success of drug candidates. First-pass metabolism is one of the major causes of poor oral bioavailability and short half-life. Traditionally, metabolic stability was evaluated at a later stage of drug discovery and required laborious manual manipulations. With the advance of high-throughput screening, combinatorial chemistry, and early profiling of drug-like properties, automated and rapid stability assays are needed to meet the increasing demand of throughput, speed, and reproducibility at earlier stages of drug discovery. The authors describe optimization of a simple, robust, high-throughput microsomal stability assay developed in a 96-well format. The assay consists of 2 automated components: robotic sample preparation for incubation and cleanup and rapid liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) analysis to determine percent remaining of the parent compound. The reagent solutions and procedural steps were optimized for automation. Variables affecting assay results were investigated. The variability introduced by microsome preparations from different sources (various vendors and batches) was studied and indicates the need for careful control. Quality control and normalization of the stability results are critical when applying the screening data, generated at different times or research sites, to discovery projects.

Simulated moving columns technique for chiral liquid chromatography.

Enantioselectivity of chiral selectors is often relatively low in chiral HPLC. For difficult chiral separations, often only partial resolution is obtained rather quickly by column and mobile phase screening, and, by trial-and-error, additional method optimization is required to achieve complete resolution. This paper describes the development of a novel column-switching technique called "simulated moving columns" (SMC) to quickly achieve complete chiral resolution on columns with limited enantioselectivity. The simulated moving columns (SMC) technique uses two (2) or three (3) short chiral HPLC columns connected in series, and forces the unresolved enantiomers to recycle exclusively through the columns until sufficient resolution is attained. In effect, SMC helps to achieve chiral resolution by virtually multiplying the column length, thus enhancing separation efficiency and resolution, without increasing backpressure. Comparison of the standard non-SMC approach with SMC, and selected applications of chiral separations of pharmaceutical drug molecules are presented. Through measurement and calculation, evaluation of off-column band broadening resulting from a two-column SMC system is provided. The results clearly indicate that SMC eliminates the significant band broadening that is inevitable in the closed-loop recycling techniques currently used in preparative chromatography. Furthermore, SMC is not only useful to enhance resolution for analytical and preparative chiral separation, but also has great potential to enhance recovery and purity for difficult chiral preparative chromatography.

Rapid method development for chiral separation in drug discovery using multi-column parallel screening and circular dichroism signal pooling.

A novel strategy for rapid chiral method development has been developed using multi-column parallel screening and circular dichroism (CD) signal pooling. Described is the first use of a customized HPLC system that integrates an HPLC auto-sampler, one pump and five divided channels with five columns and five UV detectors to screen five chiral stationary phases (CSPs) simultaneously in parallel. A high-pressure semi-prep on-line pre-filter, a six-port manifold and five individually adjusted backpressure restrictors were installed in the system which allowed the sample and mobile phase to be evenly distributed over the five columns and UV detectors. The five CSPs, namely Chiralpak AD and AS, Chiralcel OJ and OD and Whelk-O1, were screened. The system guarantees a five-fold increase in speed for chiral column scouting compared with the widely used automated sequential column switching approach, and does not have the limitations of the coupled column screening approach for enantiomers whose elution order could be reversed on CSPs. Furthermore, the five channels after the UV detectors were recombined using a reversed flow splitter into a CD detector. The pooled CD signal from the five channels was recorded to track the elution order of the resolved enantiomers and to determine their sign, positive or negative. The signal pooling allows for the effective use of a single CD detector for multiple columns since unresolved racemate has little CD signal, and observing the sign of CD signal for one of the two enantiomer UV peaks is sufficient for tracking the enantiomeric elution order.

Rapid, automated screening method for enzymatic transformations using a robotic system and supercritical fluid chromatography.

An automated screening method was developed for enzymatic transformations using a robotic system and rapid chiral supercritical fluid chromatography (SFC) analysis with a run time of 1.5 min. The method accelerates the enzyme selection process for screening biocatalysts, where a large number of enzymes are evaluated for activity and enantioselectivity. Kinetic resolution of secondary alcohols by enzymatic transesterification was used as a prototype for method development. The rapid automated method can be used effectively for screening enzymes and optimizing reaction conditions in biocatalysis.

Pharmaceutical profiling method for lipophilicity and integrity using liquid chromatography-mass spectrometry.

A method is described for the simultaneous profiling of sample lipophilicity, integrity, and purity. The method is rapid and is applicable to high throughput profiling of pharmaceutical properties in drug discovery. A short Polaris C(18) column is used with a rapid, wide-polarity mobile phase gradient, UV detection, and MS analysis. The lipophilicity of each component is estimated from a calibration curve using six drug or organic compounds and plotting their respective measured retention time versus LogD(7.4) (literature). The correlation of LogD(7.4) (literature) to LogD(7.4) (HPLC) for 60 structurally diverse drugs has a correlation coefficient r(2) of 0.89. The method is applicable to compounds with MW>200 and retention time>1.5 min for rapid, initial pharmaceutical profiling in drug discovery.

Determination of rat oral bioavailability of soy-derived phytoestrogens using an automated on-column extraction procedure and electrospray tandem mass spectrometry.

In recent years, consumption of herbal supplements as an alternative to pharmaceutical drug therapy has increased. For example, with the health claims labeling which describes the link between soy-protein and a reduced risk of coronary heart disease (CHD), the consumption of soy and soy-derived phytoestrogens has increased dramatically. That being said, the oral bioavailability of only a few soy phytoestrogens such as Daidzein and Genestein have been previously estimated. In this paper, we present the calculated percent of rat oral bioavailability of five soy-derived phytoestrogens (Genistein, Daidzein, Biochanin A, Coumestrol, and Zearalenone) in male Sprague-Dawley rats. The plasma quantitation required for the bioavailability calculation is performed by using a rapid on-line plasma extraction procedure for the quantitative analysis. To further speed up the analysis the rats were dosed using the 'n-in-one' (cassette) protocol. The rapid on-line extraction/quantitation methodology coupled to the cassette dosing analysis of phytoestrogens is the key point of this paper. The limit of quantitation (LOQ) for each compound was 1-1000 ng/ml with each plasma sample analysis taking less than 2 min. In general the percent oral bioavailability was determined to be between 11 and 28%.

High throughput artificial membrane permeability assay for blood-brain barrier.

The recent advances in high throughput screening for biological activities and combinatorial chemistry have greatly expanded the number of drug candidates. Rapid screening for BBB penetration potential early in drug discovery programs provides important information for compound selection and guidance of synthesis for desirable CNS properties. In this paper, we discuss a modification of the parallel artificial membrane permeation assay (PAMPA) for the prediction of blood-brain barrier penetration (PAMPA-BBB). The assay was developed with 30 structurally diverse commercial drugs and validated with 14 Wyeth Research compounds. The PAMPA-BBB assay has the advantages of: predicting passive blood-brain barrier penetration with high success, high throughput, low cost, and reproducibility.

Relative hydrophobicity and lipophilicity of drugs measured by aqueous two-phase partitioning, octanol-buffer partitioning and HPLC. A simple model for predicting blood-brain distribution.

Relative hydrophobicity and lipophilicity of 63 compounds with known permeability through the blood-brain barrier (BBB) was examined by partitioning in aqueous dextran-poly(ethylene glycol) two-phase system and octanol-buffer system, and by gradient RP-HPLC at pH 7.4. Combination of the relative hydrophobicity estimates, N(CH(2)) obtained by aqueous two-phase partitioning and the lipophilicity (logD(exp) or logD(HPLC)) values obtained by the shake-flask technique or HPLC technique allows one to differentiate between compounds capable of crossing the BBB and those that cannot. A simple model for predicting blood-brain distribution is proposed.

Brain and plasma exposure profiling in early drug discovery using cassette administration and fast liquid chromatography-tandem mass spectrometry.

A method using reverse phase liquid chromatography-tandem mass spectrometry and cassette administration was developed for in vivo brain and plasma exposure profiling to assist early CNS drug discovery programs. Three to four compounds were grouped in cassettes for dosing and analysis. Compounds in the cassettes were selected to minimize possible analytical interference from each other, as well as from their potential metabolites. In order to improve the confidence of cassette administration, an analogue of the study compounds, with well-established brain penetration data, was included in each cassette as a "biological internal standard". Compounds were administered to rats by intraperitoneal injection and extracted from plasma or brain homogenate by simple protein precipitation. Fast chromatographic separation was achieved by using a short narrow-bore column at a flow rate of 1.0ml/min with a fast gradient. The brain penetration of the compounds was evaluated by comparing their C(max) and AUC values in brain and plasma. This approach rapidly provided early brain penetration and plasma exposure information, thus making more of this data available to teams. Comparing the brain exposures to the EC(50) values (i.e. in vitro potency) of series compounds in the same discovery program provided another dimension of information to select lead compounds for future in vivo assessment. The method described here has been used for providing early brain penetration information in several CNS exploratory and discovery programs.

Integrated high capacity solid phase extraction-MS/MS system for pharmaceutical profiling in drug discovery.

A method is described for use in analysis of samples from pharmaceutical profiling of early drug discovery compounds. The method consists of a high capacity autosampler which injects samples into one of two solid phase extraction columns operated in parallel for alternating trapping, washing and elution into a tandem quadrupole mass spectrometer operated in multiple reaction monitoring (MRM) MS/MS mode. A primary method, which is useful for 80-90% of compounds, and a secondary method, which is useful for a majority of the remaining compounds, are described. No analytical HPLC column is used and the analysis rate is approximately 50 samples/h. Specificity is obtained using MRM analysis. Application of the method for high capacity analysis of metabolic stability samples is described.

Microbiota of healthy corals are active against fungi in a light-dependent manner.

Coral reefs are intricate ecosystems that harbor diverse organisms, including 25% of all marine fish. Healthy corals exhibit a complex symbiosis between coral polyps, endosymbiotic alga, and an array of microorganisms, called the coral holobiont. Secretion of specialized metabolites by coral microbiota is thought to contribute to the defense of this sessile organism against harmful biotic and abiotic factors. While few causative agents of coral diseases have been unequivocally identified, fungi have been implicated in the massive destruction of some soft corals worldwide. Because corals are nocturnal feeders, they may be more vulnerable to fungal infection at night, and we hypothesized that the coral microbiota would have the capability to enhance their defenses against fungi in the dark. A Pseudoalteromonas sp. isolated from a healthy octocoral displayed light-dependent antifungal properties when grown adjacent to Penicillium citrinum (P. citrinum) isolated from a diseased Gorgonian octocoral. Microbial MALDI-imaging mass spectrometry (IMS) coupled with molecular network analyses revealed that Pseudoalteromonas produced higher levels of antifungal polyketide alteramides in the dark than in the light. The alteramides were inactivated by light through a photoinduced intramolecular cyclization. Further NMR studies led to a revision of the stereochemical structure of the alteramides. Alteramide A exhibited antifungal properties and elicited changes in fungal metabolite distributions of mycotoxin citrinin and citrinadins. These data support the hypothesis that coral microbiota use abiotic factors such as light to regulate the production of metabolites with specialized functions to combat opportunistic pathogens at night.