Unprecedented Benzoquinone Motifs Reveal Post-Oligomerizational Modification of Proanthocyanidins

Proanthocyanidins (PACs) are complex flavan-3-ol polymers with stunning chemical complexity due to oxygenation patterns, oxidative phenolic ring linkages, and intricate stereochemistry of their heterocycles and inter-flavan linkages. Being promising candidates for dental restorative biomaterials, trace analysis of dentin bioactive cinnamon PACs now yielded novel trimeric (1 and 2) and tetrameric (3) PACs with unprecedented o- and p-benzoquinone motifs (benzoquinonoid PACs). Challenges in structural characterization, especially their absolute configuration, prompted the development of a new synthetic-analytical approach involving comprehensive spectroscopy, including NMR with quantum mechanics-driven 1H iterative functionalized spin analysis (HifSA) plus experimental and computational electronic circular dichroism (ECD). Vital stereochemical information was garnered from synthesizing 4-(2,5-benzoquinone)flavan-3-ols and a truncated analogue of trimer 2 as ECD models. Discovery of the first natural benzoquinonoid PACs provides new evidence to the experimentally elusive PAC biosynthesis as their formation requires two oxidative post-oligomerizational modifications (POMs) that are distinct and occur downstream from both quinone-methide-driven oligomerization and A-type linkage formation. While Nature is known to achieve structural diversity of many major compound classes by POMs, this is the first indication of PACs also following this common theme.

Anti-Microbial Activity of Aliphatic Alcohols from Chinese Black Cardamom (Amomum tsao-ko) against Mycobacterium tuberculosis H37Rv

The fruits of Amomun tsao-ko (Chinese black cardamom; Zingiberaceae) contain an abundance of essential oils, which have previously demonstrated significant antimicrobial activity. In our preliminary search for natural anti-tuberculosis agents, an acetone extract of A. tsao-ko (AAE) exhibited strong antibacterial activity against Mycobacterium tuberculosis H37Rv. Therefore, the aim of this study was to find the principal compounds in an AAE against M. tuberculosis. Nine aliphatic compounds (1−9) including a new compound (1, tsaokol B) and a new natural unsaturated aliphatic diester (6), together with three acyclic terpenoids (10−12), were isolated from an AAE by repetitive chromatography. The structures of the isolates were determined by spectroscopic data analysis. All isolates were evaluated for activity against M. tuberculosis H37Rv. Isolated compounds 1−6, and 11 had MICs ranging from 0.6−89 µg/mL. In contrast, compounds 7 to 10, and 12 had MICs that were >100 µg/mL. Tsaokol A (3) was the most active compound with MICs of 0.6 µg/mL and 1.4 µg/mL, respectively, against replicating and nonreplicating M. tuberculosis. These results are the first to illustrate the potency of tsaokol A (3) as a natural drug candidate with good selectivity for treating tuberculosis.

Design of Novel Phosphopantetheine Adenylyltransferase Inhibitors: a Potential New Approach to Tackle Mycobacterium tuberculosis

BACKGROUND

Tuberculosis (TB) has been a challenging disease worldwide, especially for the neglected poor populations. Presently, there are approximately 2 billion people infected with TB worldwide and 10 million people in the world fell ill with active TB, leading to 1.5 million deaths.

INTRODUCTION

The classic treatment is extensive and the drug and multi drug resistance of Mycobacterium tuberculosis has been a threat to the efficacy of the drugs currently used. Therefore, the rational design of new anti TB candidates is urgently needed.

METHODS

With the aim of contributing to face this challenge, 78 compounds have been proposed based on SBDD (Structure Based Drug Design) strategies applied to target the M. tuberculosis phosphopantetheine adenylyltransferase (MtPPAT) enzyme. Ligand Based Drug Design (LBDD) strategies were also used for establishing structure activity relationships (SAR) and for optimizing the structures. MtPPAT is important for the biosynthesis of coenzyme A (CoA) and it has been studied recently toward the discovery of new inhibitors.

RESULTS

After docking simulations and enthalpy calculations, the interaction of selected compounds with MtPPAT was found to be energetically favorable. The most promising compounds were then synthesized and submitted to anti M. tuberculosis and MtPPAT inhibition assays.

CONCLUSION

One of the compounds synthesized (MCP163), showed the highest activity in both of these assays.

Antimycobacterial Rufomycin Analogues from Streptomyces atratus Strain MJM3502

This study represents a systematic chemical and biological study of the rufomycin (RUF) class of cyclic heptapeptides, which our anti-TB drug discovery efforts have identified as potentially promising anti-TB agents that newly target the caseinolytic protein C1, ClpC1. Eight new RUF analogues, rufomycins NBZ1-NBZ8 (1-8), as well as five known peptides (9-13) were isolated and characterized from the Streptomyces atratus strain MJM3502. Advanced Marfey's and X-ray crystallographic analysis led to the assignment of the absolute configuration of the RUFs. Several isolates exhibited potent activity against both pathogens M. tuberculosis H37Rv and M. abscessus, paired with favorable selectivity (selectivity index >60), which collectively underscores the promise of the rufomycins as potential anti-TB drug leads.

Residual Complexity Does Impact Organic Chemistry and Drug Discovery: The Case of Rufomyazine and Rufomycin

Residual complexity (RC) involves the impact of subtle but critical structural and biological features on drug lead validation, including unexplained effects related to unidentified impurities. RC commonly plagues drug discovery efforts due to the inherent imperfections of chromatographic separation methods. The new diketopiperazine, rufomyazine (6), and the previously known antibiotic, rufomycin (7), represent a prototypical case of RC that (almost) resulted in the misassignment of biological activity. The case exemplifies that impurities well below the natural abundance of ¹³C (1.1%) can be highly relevant and calls for advanced analytical characterization of drug leads with extended molar dynamic ranges of >1:1,000 using qNMR and LC-MS. Isolated from an actinomycete strain, 6 was originally found to be active against Mycobacterium tuberculosis with a minimum inhibitory concentration (MIC) of 2 μg/mL and high selectivity. As a part of lead validation, the dipeptide was synthesized and surprisingly found to be inactive. The initially observed activity was eventually attributed to a very minor contamination (0.24% [m/m]) with a highly active cyclic peptide (MIC ∼ 0.02 μM), subsequently identified as an analogue of 7. This study illustrates the serious implications RC can exert on organic chemistry and drug discovery, and what efforts are vital to improve lead validation and efficiency, especially in NP-related drug discovery programs.

QSAR-driven design, synthesis and discovery of potent chalcone derivatives with antitubercular activity

New anti-tuberculosis (anti-TB) drugs are urgently needed to battle drug-resistant Mycobacterium tuberculosis strains and to shorten the current 6-12-month treatment regimen. In this work, we have continued the efforts to develop chalcone-based anti-TB compounds by using an in silico design and QSAR-driven approach. Initially, we developed SAR rules and binary QSAR models using literature data for targeted design of new heteroaryl chalcone compounds with anti-TB activity. Using these models, we prioritized 33 compounds for synthesis and biological evaluation. As a result, 10 heteroaryl chalcone compounds (4, 8, 9, 11, 13, 17-20, and 23) were found to exhibit nanomolar activity against replicating mycobacteria, low micromolar activity against nonreplicating bacteria, and nanomolar and micromolar against rifampin (RMP) and isoniazid (INH) monoresistant strains (rRMP and rINH) (<1 μM and <10 μM, respectively). The series also show low activity against commensal bacteria and generally show good selectivity toward M. tuberculosis, with very low cytotoxicity against Vero cells (SI = 11-545). Our results suggest that our designed heteroaryl chalcone compounds, due to their high potency and selectivity, are promising anti-TB agents.

Pharmacokinetic Enhancement of the Hepatitis C Virus Protease Inhibitors VX-950 and SCH 503034 by Co-Dosing with Ritonavir

Inhibitors of hepatitis C virus (HCV) protease have shown marked antiviral activity in short-term clinical studies in HCV-infected individuals. The interaction of the investigational HCV protease inhibitors VX-950 and SCH 503034 with ritonavir, a potent inhibitor of cytochrome P450 3A, was studied in vitro and in vivo. In rat and human liver microsomes, the metabolism of VX-950 and SCH 503034 was strongly inhibited by the presence of 4 µM ritonavir. Upon co-dosing either VX-950 or SCH 503034 with ritonavir in rats, plasma exposure of the HCV protease inhibitors was increased by >15-fold, and plasma concentrations 8 h after dosing were increased by >50-fold. A human pharmacokinetic model of VX-950 co-administered with low-dose ritonavir suggested that improved efficacy and/or dosing convenience may be feasible by pharmacokinetic enhancement with ritonavir.

The Generally Useful Estimate of Solvent Systems (GUESS) method enables the rapid purification of methylpyridoxine regioisomers by countercurrent chromatography

The TLC-based Generally Useful Estimate of Solvent Systems (GUESS) method was employed for countercurrent chromatography solvent system selection, in order to separate the three synthetic isomers: 3-O-methylpyridoxine, 4'-O-methylpyridoxine (ginkgotoxin), and 5'-O-methylpyridoxine. The Rf values of the three isomers indicated that ChMWat+2 (chloroform-methanol-water 10:5:5, v/v/v) was appropriate for the countercurrent separation. The isomer separation was highly selective and demonstrated that the TLC-based GUESS method can accelerate solvent system selection for countercurrent separation. Accordingly, the study re-emphasizes the practicality of TLC as a tool to facilitate the rapid development of new countercurrent and centrifugal partition chromatography methods for this solvent system. Purity and structure characterization of all samples was performed by quantitative (1)H NMR.

Quantification of a botanical negative marker without an identical standard: ginkgotoxin in Ginkgo biloba

A new strategy for the analysis of natural products uses a combination of quantitative (1)H NMR (qHNMR) and adsorbent-free countercurrent separation (CS) methodology to establish a quantification method for ginkgotoxin (4'-O-methylpyridoxine) in Ginkgo biloba preparations. The target analyte was concentrated in a one-step CS process using the ChMWat +2 solvent system (CHCl3-MeOH-H2O, 10:5:5) and subsequently assayed by qHNMR. While commercial G. biloba seeds contained 59 μg of ginkgotoxin per seed, the compound was below the limit of detection (9 ppm) in a typical leaf extract. Due to the enrichment potential and loss-free operation of CS, the combination of CS and qHNMR is a generally suitable approach for threshold assays aimed at quantifying target compounds such as botanical negative markers at the low ppm level. As the proof of principle is demonstrated for relatively small CS capacities (20 mL, 1:40 loading) and modest NMR sensitivity (n = 16, 400 MHz, 5 mm RT probe), the approach can be adapted to quantification at the ppb level. The procedure enables the quantification of a botanical negative marker in the absence of identical reference material, which otherwise is a prerequisite for LC-based assays.

A novel indigoid anti-tuberculosis agent

The structure of a novel indigoid component was characterized by X-ray crystallography. This compound exhibited excellent anti-tuberculosis activity against Mycobacterium tuberculosis H37Rv in whole cell culture showing a submicromolar minimum inhibitory concentration (MIC). A synthesis of this molecule was designed and carried out to produce sufficient material for further testing. The in vitro profile, structure, and first synthesis of this indigoid component is reported.

Chlorinated coumarins from the polypore mushroom Fomitopsis officinalis and their activity against Mycobacterium tuberculosis

An EtOH extract of the polypore mushroom Fomitopsis officinalis afforded two new naturally occurring chlorinated coumarins, which were identified as the previously synthesized compounds 6-chloro-4-phenyl-2H-chromen-2-one (1) and ethyl 6-chloro-2-oxo-4-phenyl-2H-chromen-3-carboxylate (2). The structures of the two isolates were deduced by ab initio spectroscopic methods and confirmed by chemical synthesis. In addition, an analogue of each was synthesized as 7-chloro-4-phenyl-2H-chromen-2-one (3) and ethyl 7-chloro-2-oxo-4-phenyl-2H-chromen-3-carboxylate (4). All four compounds were characterized physicochemically, and their antimicrobial activity profiles revealed a narrow spectrum of activity with lowest MICs against the Mycobacterium tuberculosis complex.

Synthesis of Substituted Isatins

Isatins are valuable intermediates for heterocyclic chemistry. Most of the common methods for their production are less than adequate when the number and lipophilicity of substituents on the targeted isatin are increased. Our group desired such molecules and identified an alternative method for their production.

P1-substituted symmetry-based human immunodeficiency virus protease inhibitors with potent antiviral activity against drug-resistant viruses

Because there is currently no cure for HIV infection, patients must remain on long-term drug therapy, leading to concerns over potential drug side effects and the emergence of drug resistance. For this reason, new and safe antiretroviral agents with improved potency against drug-resistant strains of HIV are needed. A series of HIV protease inhibitors (PIs) with potent activity against both wild-type (WT) virus and drug-resistant strains of HIV was designed and synthesized. The incorporation of substituents with hydrogen bond donor and acceptor groups at the P1 position of our symmetry-based inhibitor series resulted in significant potency improvements against the resistant mutants. By this approach, several compounds, such as 13, 24, and 29, were identified that demonstrated similar or improved potencies compared to 1 against highly mutated strains of HIV derived from patients who previously failed HIV PI therapy. Overall, compound 13 demonstrated the best balance of potency against drug resistant strains of HIV and oral bioavailability in pharmacokinetic studies. X-ray analysis of an HIV PI with an improved resistance profile bound to WT HIV protease is also reported.

Identification of proteasome gene regulation in a rat model for HIV protease inhibitor-induced hyperlipidemia

Patients treated with highly active antiretroviral therapy may develop metabolic side effects such as hyperlipidemia, insulin resistance, lipoatrophy and lactic acidosis. The pathophysiology of these metabolic abnormalities is unknown, although some, e.g., lactic acidosis and lipoatrophy, are more associated with nucleoside use while protease inhibitors (PIs) have been shown to contribute to hyperlipidemia and insulin resistance. Identifying new PIs that are not associated with dyslipidemia has been hindered by the lack of mechanistic information and the unavailability of relevant animal models. In order to understand the molecular mechanism behind the hyperlipidemia associated with other protease inhibitors, and to develop a more effective, faster screen for compounds with this liability, we have analyzed expression profiles from PI-treated animals. Previously, we have shown that treatment of rats with ritonavir results in increases in the expression of proteasomal subunit genes in the liver. We show this increase is similar in rats treated with bortezomib, a proteasome inhibitor. In addition, we have treated rats with additional protease inhibitors, including atazanavir, which is associated with lower rates of lipid elevations in the clinic when administered in the absence of ritonavir. Our results indicate a strong correlation between proteasomal induction and lipid elevations, and have allowed us to develop a rapid screen for identifying novel PIs that do not induce the proteasome.

Synthesis and evaluation of inhibitors of cytochrome P450 3A (CYP3A) for pharmacokinetic enhancement of drugs

The HIV protease inhibitor ritonavir (RTV) is also a potent inhibitor of the metabolizing enzyme cytochrome P450 3A (CYP3A) and is clinically useful in HIV therapy in its ability to enhance human plasma levels of other HIV protease inhibitors (PIs). A novel series of CYP3A inhibitors was designed around the structural elements of RTV believed to be important to CYP3A inhibition, with general design features being the attachment of groups that mimic the P2-P3 segment of RTV to a soluble core. Several analogs were found to strongly enhance plasma levels of lopinavir (LPV), including 8, which compares favorably with RTV in the same model. Interestingly, an inverse correlation between in vitro inhibition of CYP3A and elevation of LPV was observed. The compounds described in this study may be useful for enhancing the pharmacokinetics of drugs that are metabolized by CYP3A.

Synthesis and biological characterization of B-ring amino analogues of potent benzothiadiazine hepatitis C virus polymerase inhibitors

Benzothiadiazine inhibitors of the HCV NS5B RNA-dependent RNA polymerase are an important class of non-nucleoside inhibitors that have received considerable attention in the search for novel HCV therapeutics. Research in our laboratories has identified a novel series of tetracyclic benzothiadiazine inhibitors of HCV polymerase bearing a benzylamino substituent on the B-ring. Compounds in this series exhibit low-nanomolar activities in both genotypes 1a and 1b polymerase inhibition assays and subgenomic replicon assays. Optimization of pharmacokinetic properties in rat led to compound 30, which has good oral bioavailability (F = 56%) and a favorable tissue distribution drug profile, with high liver to plasma ratios. Compound 30 is a potent inhibitor in replicon assays, with EC(50) values of 10 and 6 nM against genotypes 1a and 1b, respectively.

Hepatitis C NS5B polymerase inhibitors: 4,4-Dialkyl-1-hydroxy-3-oxo-3,4-dihydronaphthalene-3-yl benzothiadiazine derivatives

4,4-Dialkyl-1-hydroxy-3-oxo-3.4-dihydronaphthalene-3-yl benzothiadiazine derivatives were synthesized and evaluated as inhibitors of genotypes 1a and 1b HCV NS5B polymerase. A number of these compounds exhibited potent activity against genotypes 1a and 1b HCV polymerase in both enzymatic and cell culture activities. A representative compound also showed favorable pharmacokinetics in the rat.

Discovery of imidazolidine-2,4-dione-linked HIV protease inhibitors with activity against lopinavir-resistant mutant HIV

A new series of HIV protease inhibitors has been designed and synthesized based on the combination of the (R)-(hydroxyethylamino)sulfonamide isostere and the cyclic urea component of lopinavir. The series was optimized by replacing the 6-membered cyclic urea linker with an imidazolidine-2,4-dione which readily underwent N-alkylation to incorporate various methylene-linked heterocycle groups that bind favorably in site 3 of HIV protease. Significant improvements compared to lopinavir were seen in cell culture activity versus wild-type virus (pNL4-3) and the lopinavir-resistant mutant virus A17 (generated by in vitro serial passage of HIV-1 (pNL4-3) in MT-4 cells). Select imidazolidine-2,4-dione containing PIs were also more effective at inhibiting highly resistant patient isolates Pt1 and Pt2 than lopinavir. Pharmacokinetic data collected for compounds in this series varied considerably when coadministered orally in the rat with an equal amount of ritonavir (5 mg/kg each). The AUC values ranged from 0.144 to 12.33 microg h/mL.

Practical preclinical model for assessing the potential for unconjugated hyperbilirubinemia produced by human immunodeficiency virus protease inhibitors

A practical preclinical model for the hyperbilirubinemia produced by human immunodeficiency virus protease inhibitors has been developed. Indinavir and atazanavir produced significant hyperbilirubinemia, whereas amprenavir, the negative control, was indistinguishable from the ritonavir booster dose. This model was used to disqualify an exploratory protease inhibitor from development.

Synthesis, antiviral activity, and pharmacokinetic evaluation of P3 pyridylmethyl analogs of oximinoarylsulfonyl HIV-1 protease inhibitors

As a continuation of the recently communicated discovery of oximinoarylsulfonamides as potent inhibitors of HIV-1 aspartyl protease, compounds bearing pyridylmethyl substituents at P3 were designed and synthesized. Potent analogs in this series provided low single-digit nanomolar EC50 values against both wild-type HIV and resistant mutant virus (A17), attenuated some 3- to 12-fold in the presence of 50% human serum. Pharmacokinetic results for compounds in this series showed good to excellent exposure when co-administered orally with an equal amount of ritonavir (5mg/kg each) in the rat, with average AUC >8 microg h/mL. Similar dosing in dog resulted in significantly lower plasma levels (average AUC <2 microg h/mL). The 3-pyridylmethyl analog 30 gave the best overall exposure (rat AUC=7.1 microg h/mL and dog AUC=4.9 microg h/mL), however, this compound was found to be a potent inhibitor of cytochrome P450 3A (Ki=2.4 nM).

Synthesis and activity of N-acyl azacyclic urea HIV-1 protease inhibitors with high potency against multiple drug resistant viral strains

As part of our efforts to identify potent HIV-1 protease inhibitors that are active against resistant viral strains, structural modification of the azacyclic urea (I) was undertaken by incorporating acyl groups as P(1)' ligands. The extensive SAR study has yielded a series of N-acyl azacyclic ureas (II), which are highly potent against both wild-type and multiple PI-resistant viral strains.

Oximinoarylsulfonamides as potent HIV protease inhibitors

The need for a potent HIV protease inhibitor (PI) to combat emerging PI-resistant viruses is anticipated. Analogs formulated from the combination of structural fragments of Ritonavir, Lopinavir, and Amprenavir were synthesized. Analogs containing the oxime pharmacophore were found to have improved activities against both wild type and resistant (A17) viruses. The synthesis and structure-activity relationships (SAR) based upon the in vitro IC50 of this series of compounds are reported.

Synthesis and antiviral activity of P1′ arylsulfonamide azacyclic urea HIV protease inhibitors

A series of novel azacyclic urea HIV protease inhibitors bearing a benzenesulfonamide group at P1' were synthesized utilizing a parallel synthesis method. Structural studies of early analogs bound in the enzyme active site were used to design more potent inhibitors. The effects of substituting the P1' benzenesulfonyl group on antiviral activity and protein binding are described.

Mutations conferring resistance to a potent hepatitis C virus serine protease inhibitor in vitro

BILN 2061 is a novel, specific hepatitis C virus (HCV) NS3 serine protease inhibitor discovered by Boehringer Ingelheim that has shown potent activity against HCV replicons in tissue culture and is currently under clinical investigation for the treatment of HCV infection. The poor fidelity of the HCV RNA-dependent RNA polymerase will likely lead to the development of drug-resistant viruses in treated patients. The development of resistance to BILN 2061 was studied by the in vitro passage of HCV genotype 1b replicon cells in the presence of a fixed concentration of the drug. Three weeks posttreatment, four colonies were expanded for genotypic and phenotypic characterization. The 50% inhibitory concentrations of BILN 2061 for these colonies were 72- to 1,228-fold higher than that for the wild-type replicon. Sequencing of the individual colonies identified several mutations in the NS3 serine protease gene. Molecular clones containing the single amino acid substitution A156T, R155Q, or D168V resulted in 357-fold, 24-fold, and 144-fold reductions in susceptibility to BILN 2061, respectively, compared to the level of susceptibility shown by the wild-type replicon. Modeling studies indicate that all three of these residues are located in close proximity to the inhibitor binding site. These findings, in addition to the three-dimensional structure analysis of the NS3/NS4A serine protease inhibitor complex, provide a strategic guide for the development of next-generation inhibitors of HCV NS3/NS4A serine protease.

Enantioselective synthesis of antiinfluenza compound A-315675

Drug discovery efforts at Abbott Laboratories have led to the identification of influenza neuraminidase inhibitor A-315675 (1) as a candidate for development as an antiinfluenza drug. A convergent, stereoselective synthesis of this highly functionalized pyrrolidine is reported that utilizes pyrrolinone 2 as the key intermediate. The C5, C6 stereochemistry was established through a diastereoselective condensation of chiral imine compound 3 with silyloxypyrrole 4 to give pyrrolinone 2. The stereochemical outcome of this reaction depended critically on the choice of the imine functional group (FG), with tritylsulfenyl and (R)-toluenesulfinyl providing the desired products in good yields as crystalline intermediates. Conversion of pyrrolinone 2 into 1 was accomplished in seven subsequent steps, including Michael addition of cis-1-propenylcuprate at C4 and introduction of a cyano group as a carboxylic acid equivalent at C2.

Total synthesis and antifungal evaluation of cyclic aminohexapeptides

The need for new therapies to treat systemic fungal infections continues to rise. Naturally occurring hexapeptide echinocandin B (1) has shown potent antifungal activity via its inhibition of the synthesis of beta-1,3 glucan, a key fungal cell wall component. Although this series of agents has been limited thus far based on their physicochemical characteristics, we have found that the synthesis of analogues bearing an aminoproline residue in the 'northwest' position imparts greatly improved water solubility (> 5 mg/mL). The synthesis and structure-activity relationships (SAR) based on whole cell and upon in vivo activity of the series of compounds are reported.

Design and preparation of cyclopeptamine antifungal agents

The lack of agents for infections caused by pathogenic fungi has demanded further investigation of a key lead structure which has shown promise, echinocandin B. In recent years, two analogs of this cyclic hexapeptide are proceeding through the clinic exhibiting proof of concept for the target of these drugs. This target, the ss-1,3-glucan synthesis complex, produces the majority of fungal cell wall glucan in many of the most pathogenic fungi such as Candida. A methodical structure-activity relationship review of several major fragments of these highly functionalized molecules is described. This information is useful for determination of the minimum functional/structural requirements for design of an optimal compound in this series. Analogs are presented with their accompanying whole cell antifungal activities.

Synthesis of 9-deoxo-4''-deoxy-6,9-epoxyerythromycin derivatives: novel and acid-stable motilides

In our quest toward the discovery of highly potent and acid-stable motilides, novel 4"-deoxy derivatives of 9-deoxo-6, 9-epoxyerythromycin were designed, synthesized, and evaluated for their gastrointestinal prokinetic activities. These compounds, in their 9R configuration, were more potent than their 6,9-enol ether homologues in inducing well-coordinated smooth muscle contractions in an in vitro rabbit duodenal assay: e.g., (9R), (8S)-9-deoxo-4"-deoxy-3'-N-desmethyl-3'-N-ethyl-6, 9-epoxyerythromycin A (10) and (9R), (8S)-9-deoxo-4"-deoxy-3'-N-desmethyl-3'-N-ethanol-6, 9-epoxyerythromycin A (15) had a pED50 of 8.54 and 8.11 compared to a pED50 of 7.22 for compound 2 (ABT-229). Reduction of the 6,9-enol ether, which was aimed at improving the acid stability, afforded the most stable motilides to date with t1/2 of 5.5 h for 10 and 15. Compounds 10 and 15 bind specifically to rabbit antral smooth muscle motilin receptors with pIC50 values of 8.52 and 8.70.

Cellular accumulation, localization, and activity of a synthetic cyclopeptamine in fungi

A novel synthetic cyclopeptamine, A172013, rapidly accumulated by passive diffusion into Candida albicans CCH442. Drug influx could not be totally facilitated by the membrane-bound target, beta-(1,3)-glucan synthase, since accumulation was unsaturable at drug concentrations up to 10 microg/ml (about 1.6 x 10(-7) molecules/cell), or 25x MIC. About 55 and 23% of the cell-incorporated drug was associated with the cell wall and protoplasts, respectively. Isolated microsomes contained 95% of the protoplast-associated drug, which was fully active against glucan synthesis in vitro. Drug (0.1 microg/ml) accumulation was rapid and complete after 5 min in several fungi tested, including a lipopeptide/cyclopeptamine-resistant strain of C. albicans (LP3-1). The compound penetrated to comparable levels in both yeast and hyphal forms of C. albicans, and accumulation in Aspergillus niger was 20% that in C. albicans. These data indicated that drug-cell interactions were driven by the amphiphilic nature of the compound and that the cell wall served as a major drug reservoir.

Risk factors related to age-associated hearing loss in the speech frequencies

This paper examines the relationship between several risk factors and the development of age-associated hearing loss in the speech frequencies. Hearing loss is defined as an average threshold level of 30 dB HL or greater at the frequencies of 0.5, 1, 2, and 3 kHz. Hearing thresholds from 0.5 to 8 kHz using a pulse-tone tracking procedure were collected on participants of the Baltimore Longitudinal study of Aging since 1965. A proportional hazards regression model was used to study the relationship between several risk factors that have previously been found to be associated with numerous health-related outcomes and the length of follow-up time until the occurrence of unilateral or bilateral hearing loss in a screened group of 531 men. Risk factors considered are age, blood pressure, and alcohol and cigarette consumption. After controlling for age, only systolic blood pressure showed a significant relationship with hearing loss in the speech frequencies (p < .05). Since blood pressure is a modifiable risk factor, these results suggest that preventing hypertension might contribute to an effective program for the prevention of apparent age-associated hearing loss.

Preclinical in vivo efficacy of two 9-dihydrotaxane analogues against human and murine tumours

Two 9-dihydrotaxane analogues were synthesised and tested for in vitro potency and in vivo efficacy against murine and human tumour xenografts in mice. The in vitro potency of 9-dihydrotaxol (9-DH-t) and 10-deacetyl-9-dihydrotaxol (10-DeAc-9-DH-t) was generally less than that of paclitaxel against human and murine tumour cells. However, both analogues were at least 20-fold more soluble than paclitaxel in water. The analogues yielded cure rates > or = 60% against human MX-1 solid tumour xenografts in mice, compared with a cure rate of 10% for mice treated with paclitaxel. Both of the analogues were more effective than paclitaxel for treatment of murine M109 solid tumour in mice. 10-DeAc-9-DH-t was as effective as paclitaxel against murine B16 ascites tumour, while 9-DH-t was less effective. Both 10-DeAc-9-DH-t and 9-DH-t were demonstrably less toxic than paclitaxel. At equal dosages 9-DH-t produced serum concentrations greater than paclitaxel, while 10-DeAc-9-DH-t yielded serum concentrations less than paclitaxel. However, the decrease in toxicity of 9-DH-t and 10-DeAc-9-DH-t allowed a 4-fold increase in daily dosage. These two 9-dihydrotaxane analogues yielded favourable preclinical data and demonstrated good potential for further development.

Synthesis of 4"-deoxy motilides: identification of a potent and orally active prokinetic drug candidate

As an approach to discovering highly potent motilides with oral activity, novel 4"-deoxy derivatives of 8,9-anhydroerythromycin 6,9-hemiacetal were designed, synthesized, and evaluated for their gastrointestinal prokinetic activities. These compounds were orders of magnitude more potent than their 4"-hydroxy analogs in inducing smooth muscle contractions in an in vitro rabbit duodenal assay. Removal of the 12-hydroxy group, which was aimed at improving oral bioavailability, also afforded further potentiation in in vitro activity, leading to the identification of 8,9-anhydro-4"-deoxy-3'-N-desmethyl-3'-N-ethylerythromycin B 6,9-hemiacetal (ABT-229) as a potential prokinetic drug. ABT-229 was > 300,000 times more potent than erythromycin in vitro and had 39% oral bioavailability in dog compared to its 4",12-dihydroxy congener (EM-523), which was only 400 times more potent than erythromycin and had relatively low (1.4%) oral bioavailability.

Antitumor activity of 9(R)-dihydrotaxane analogs

A novel reduced taxane, 13-acetyl-9(R)-dihydrobaccatin III (1) has been isolated from Taxus canadensis. The selective C-13 deacetylation of this isolate has allowed for the preparation of a wide variety of 9(R)-dihydrotaxane analogs. In general, this series has shown greater stability and water solubility than the 9-carbonyl series while retaining antimicrotubule and tumor cell cytotoxicity activities relative to taxol. Placement of polar functionalities at the C-7 position results in loss of activity whereas alkylation or acylation of either C-7 or C-9 hydroxyl groups ameliorate the activity.

Gender differences in a longitudinal study of age-associated hearing loss

Current studies are inconclusive regarding specific patterns of gender differences in age-associated hearing loss. This paper presents results from the largest and longest longitudinal study reported to date of changes in pure-tone hearing thresholds in men and women screened for otological disorders and noise-induced hearing loss. Since 1965, the Baltimore Longitudinal Study of Aging has collected hearing thresholds from 500 to 8000 Hz using a pulsed-tone tracking procedure. Mixed-effects regression models were used to estimate longitudinal patterns of change in hearing thresholds in 681 men and 416 women with no evidence of otological disease, unilateral hearing loss, or noise-induced hearing loss. The results show (1) hearing sensitivity declines more than twice as fast in men as in women at most ages and frequencies, (2) longitudinal declines in hearing sensitivity are detectable at all frequencies among men by age 30, but the age of onset of decline is later in women at most frequencies and varies by frequency in women, (3) women have more sensitive hearing than men at frequencies above 1000 Hz but men have more sensitive hearing than women at lower frequencies, (4) learning effects bias cross-sectional and short-term longitudinal studies, and (5) hearing levels and longitudinal patterns of change are highly variable, even in this highly selected group. These longitudinal findings document gender differences in hearing levels and show that age-associated hearing loss occurs even in a group with relatively low-noise occupations and with no evidence of noise-induced hearing loss.

Synthesis and biological evaluation of C-3'-modified analogs of 9(R)-dihydrotaxol

Taxol (1) is considered a most exciting new drug in cancer chemotherapy. The promising antitumor activity of 9(R)-dihydrotaxol (3) encouraged us to further explore the structure-activity relationship of this new member of the taxane family. Studies indicated that the C-13 side chain of taxol is indispensable for antitumor activity and that the natural substitution pattern of a 2'(R)-hydroxy and a 3'(S)-acylamino group might be optimal. However, relatively little is known about the effects of the 3'-phenyl ring on activity. The synthesis and biological evaluation of analogs of 3 modified at the C-3' position are described. This study revealed that the 3'-phenyl ring was not required for activity and identified several compounds which had equal or greater in vitro and in vivo activity than taxol.