Inhibiting protein–amyloid interactions with small molecules: A surface chemistry approach

This paper presents a surface-based approach to inhibit the binding of proteins to Alzheimer's-related beta-amyloid (Abeta) fibrils with small molecules. It reports the idea of using an intracellular, disease-related fibril as a material whose surface can be coated with small molecules. Using an ELISA-based assay, molecular surface coatings with thioflavin T are shown to inhibit 65+/-10% of the binding of two different anti-Abeta IgGs to Abeta fibrils. A molecular surface coating with 3,6-diamino acridine was able to inhibit 76+/-10% of the binding of an anti-Abeta IgG to Abeta fibrils. Maximal inhibition of these protein-amyloid interactions appears in the low to mid-micromolar range of small molecule. This demonstration that molecular surface coatings can be used to attenuate the interaction of proteins with these fibrils suggests a potentially new strategy for therapeutics in neurodegenerative amyloid diseases.

Synthesis and Structure−Activity Relationships of 3-[(2-Methyl-1,3-thiazol-4-yl)ethynyl]pyridine Analogues as Potent, Noncompetitive Metabotropic Glutamate Receptor Subtype 5 Antagonists; Search for Cocaine Medications

Recent genetic and pharmacological studies have suggested that the metabotropic glutamate receptor subtype 5 (mGluR5) may represent a druggable target in identifying new therapeutics for the treatment of various central nervous system disorders including drug abuse. In particular, considerable attention in the mGluR5 field has been devoted to identifying ligands that bind to the allosteric modulatory site, distinct from the site for the primary agonist glutamate. Both 2-methyl-6-(phenylethynyl)pyridine (MPEP) and its analogue 3-[(2-methyl-4-thiazolyl)ethynyl]pyridine (MTEP) have been shown to be selective and potent noncompetitive antagonists of mGluR5. Because of results presented in this study showing that MTEP prevents the reinstatement of cocaine self-administration caused by the presentation of environmental cues previously associated with cocaine availability, we have prepared a series of analogues of MTEP with the aim of gaining a better understanding of the structural features relevant to its antagonist potency and with the ultimate aim of investigating the effects of such compounds in blunting the self-administration of cocaine. These efforts have led to the identification of compounds showing higher potency as mGluR5 antagonists than either MPEP or MTEP. Two compounds 19 and 59 exhibited functional activity as mGluR5 antagonists that are 490 and 230 times, respectively, better than that of MTEP.

Bioactive natural and semisynthetic latrunculins

Marine-derived macrolides latrunculins A and B, of the Red Sea sponge Negombata magnifica, are the first marine natural products that have been found to reversibly bind to actin monomers and to disrupt its organization. Latrunculins are structurally related to many antimicrobial and antiangiogenic macrolides. Several grams of latrunculin B (1), together with a new latrunculin named latrunculin T (2), were isolated from a recent collection of N. magnifica. Semisynthetic modifications of 1, including acetylation, acetalization, and N-hydroxymethylation, afforded four new (4, 5, 7, 8) and two known (6 and 9) semisynthetic analogues. Specifically, 15-O-methyllatrunculin B (6) showed a promising antiangiogenic activity in a chick chorioallantoic membrane assay and antimigratory activity in Boyden's chamber assay. Moreover, latrunculin B (1) and the new N-acetyllatrunculin B (4) displayed potent antimigratory activity in a wound-healing assay. Natural and semisynthetic latrunculins showed potent antimicrobial activity against Candida albicans, Saccharomyces cerevisiae, Staphylococcus aureus, and Bacillus cereus. Latrunculins are potential leads that can be developed as anticancer and antimicrobial agents.

N-(Aryl)-4-(azolylethyl)thiazole-5-carboxamides: Novel potent inhibitors of VEGF receptors I and II

Novel potent derivatives of N-(aryl)-4-(azolylethyl)thiazole-5-carboxamides are described as inhibitors of vascular endothelial growth factor receptor II (VEGFR-2). Several compounds display VEGFR-2 inhibitory activity reaching IC(50)<100 nM in both enzymatic and cellular assays. The compounds also inhibit the related tyrosine kinase, VEGFR-1. By controlling the substitution pattern on the 5-carboxamido pharmacophore, both dual and specific VEGFR-2 thiazoles were identified.

Thiazole orange, a DNA-binding photosensitizer with flexible structure, can inactivate pathogens in red blood cell suspensions while maintaining red cell storage properties

BACKGROUND

Development of a robust pathogen reduction system for red cells (RBCs) utilizing photosensitive dyes has been constrained by hemolysis, usually mediated by reactive oxygen species emanating from dye free in solution as well as dye bound to the RBC membrane. The RBC binding properties of thiazole orange (TO), a flexible nucleic acid intercalating cyanine dye that predominantly acts as a photosensitizer only when bound, were assessed along with its virucidal, bactericidal, and light-induced hemolytic activities.

STUDY DESIGN AND METHODS

Leukodepleted 20% hematocrit RBCs suspended in Erythrosol (RAS-2) were oxygenated, inoculated with test organisms, incubated with TO, and illuminated. Control and treated samples were analyzed by appropriate assay. Identically prepared, but uncontaminated samples were phototreated, concentrated to 45% hematocrit, and assayed for potassium leakage, hemolysis, and ATP during storage.

RESULTS

Approximately 21 percent TO bound to RBCs. Phototreatment inactivated from 5.4 to 7.1 log(10) of 5 tested viruses and from 2.3 to greater than 7.0 log(10) of 8 tested bacteria. Phototreated RBCs exhibited only slightly increased hemolysis, moderately elevated potassium efflux, and similar levels of ATP compared to controls.

CONCLUSION

TO can photoinactivate several model viruses and pathogens in RBCs under conditions that produce limited hemolysis without the addition of quenchers or competitive inhibitors.

Nonfibrous β-structured aggregation of an Aβ model peptide (Ad-2α) on GM1/DPPC mixed monolayer surfaces

Adsorption and aggregation of transformed peptides and proteins onto the cell membrane surface is commonly associated with forms of amyloidosis such as Alzheimer's disease and prion disease. To address dynamic features of these pathological phenomena molecularly, the in situ Ad-2alpha model peptide deposition on glycolipid-containing monolayers was studied by using a 9 MHz quartz-crystal microbalance (QCM). The Ad-2alpha peptide has two amphiphilic alpha-helix segments, each modified with a 1-adamantanecarbonyl group at the N-terminal as a hydrophobic defect. The peptide folds in a 2alpha-helix structure in the bulk solution. In the presence of mixed monolayers of glycolipids (GM1, asialo-GM1, GM3, or LacCer) and/or dipalmitoyl phosphatidylcholine (DPPC) laminated on the QCM plate, the peptide deposition and the conformational change to beta-structure on the monolayers were accelerated. The adsorption kinetics and the amount of Ad-2alpha were dependent on the sort and contents of the glycolipid in the DPPC matrix. Although the Ad-2alpha peptide adsorbs onto most of the glycolipid membranes as monolayer coverage, it adsorbed largely onto the GM1/DPPC (30/70 mol%) mixed monolayer with characteristic kinetic behaviors. The accumulation of beta-structured nonfibrous aggregations was confirmed by AFM and fluorescence microscopy with Thioflavin T (ThT).

Mutagenesis of the central hydrophobic cluster in Abeta42 Alzheimer's peptide. Side-chain properties correlate with aggregation propensities

Protein misfolding and deposition underlie an increasing number of debilitating human disorders. Alzheimer's disease is pathologically characterized by the presence of numerous insoluble amyloid plaques in the brain, composed primarily of the 42 amino acid human beta-amyloid peptide (Abeta42). Disease-linked mutations in Abeta42 occur in or near a central hydrophobic cluster comprising residues 17-21. We exploited the ability of green fluorescent protein to act as a reporter of the aggregation of upstream fused Abeta42 variants to characterize the effects of a large set of single-point mutations at the central position of this hydrophobic sequence as well as substitutions linked to early onset of the disease located in or close to this region. The aggregational properties of the different protein variants clearly correlated with changes in the intrinsic physicochemical properties of the side chains at the point of mutation. Reduction in hydrophobicity and beta-sheet propensity resulted in an increase of in vivo fluorescence indicating disruption of aggregation, as confirmed by the in vitro analysis of synthetic Abeta42 variants. The results confirm the key role played by the central hydrophobic stretch on Abeta42 deposition and support the hypothesis that sequence tunes the aggregation propensities of polypeptides.

Detection of oncoprotein platelet-derived growth factor using a fluorescent signaling complex of an aptamer and TOTO

There have recently been advances in the application of aptamers, a new class of nucleic acids that bind specifically with target proteins, as protein recognition probes for biomedical study. The development of a signaling aptamer with the capability of simple and rapid real-time detection of disease-related proteins has attracted increasing interest. We have recently reported a new protein-detection strategy using a signaling aptamer based on a DNA molecular light-switching complex, [Ru(phen)2(dppz)]2+. In this work we have used the commercially available DNA-intercalating dye, TOTO, to replace [Ru(phen)2(dppz)]2+ for detection of oncoprotein platelet-derived growth factor BB (PDGF-BB), a potential cancer marker. Taking advantage of the high affinity of the aptamer to PDGF-BB and the sensitive fluorescence change of the aptamer-TOTO signaling complex on protein binding, PDGF-BB was detected in physiological buffer with high selectivity and sensitivity. The detection limit was 0.1 nmol L(-1), which was better than that of other reported aptamer-based methods for PDGF-BB, including that using [Ru(phen)2(dppz)]2+. The method is very simple with no need for covalent labeling of the aptamer or probe synthesis. It facilitates wide application of the signaling mechanism to the analysis and study of cancer markers and other proteins.

Novel inhibitors of hepatitis C virus RNA-dependent RNA polymerases

Hepatitis C virus (HCV) is a major cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma worldwide-and is the main cause of adult liver transplants in developed nations. We have identified a class of novel and specific inhibitors of HCV NS5B RNA-dependent RNA polymerase (RdRp) activity in vitro. Characterization of two such inhibitors, COMPOUND1 (5-(4-chlorophenylmethylene)-3-(benzenesulfonylamino)-4-oxxo-2-thionothiazolidine) and COMPOUND2 (5-(4-bromophenylmethylene)-3-(benzenesulfonylamino)-4-oxxo-2-thionothiazolidine), is reported here. With IC(50) values of 0.54muM and 0.44muM, respectively, they are reversible and non-competitive with nucleotides. Biochemical and structural studies have suggested that these compounds can inhibit the initiation of the RdRp reaction. Interestingly, these inhibitors appear to form a reversible covalent bond with the NS5B cysteine 366, a residue that is not only conserved among all HCV genotypes and a large family of viruses but also required for full NS5B RdRp activity. This may reduce the potential resistance of the viruses to this class of inhibitors.

Chemoenzymatic approaches for streamlined detection of active site modifications on thiotemplate assembly lines using mass spectrometry

For the direct interrogation of peptides harboring covalently modified serines in nonribosomal peptide synthetases, streamlined methodologies described here employ proteolysis and reporter-coenzyme A analogues of four types. The chromophoric and fluorescent coenzyme A analogues pyrene-maleimidyl-S-CoA and BODIPY-FL-N-(2-aminoethyl)maleimidyl-S-CoA were enzymatically loaded onto the active site serines harbored in the ArCP, PCP1, and PCP2 thiolation domains of PchE and PchF, the nonribosomal peptide synthetases responsible for the biosynthesis of the siderophore pyochelin. During the chromatographic separation of cyanogen bromide digests, observation of the absorbance (at 338 and 504 nm) or fluorescence (after irradiation at 365 nm) enabled the selective detection of peptides containing each active site serine. This resulted in quick detection of each active site peptide by Fourier transform mass spectrometry in the fully reconstituted pyochelin system. The loading of short acyl chain reporters in equimolar quantities permitted further insights into digestion heterogeneity and side reactions by virtue of a mass shift signature on each active site peptide. The chromatographic shift of the reporter-loaded peptides relative to peptides carrying on pathway intermediates was 2 min at 7 kDa, providing a general strategy for efficient localization of "carrier" peptides in complex digests of thiotemplate enzymes. Also, the use of the affinity reporter, biotin-maleimidyl-S-coenzyme A, permitted the isolation of intact synthetases at high purity via removal of contaminating Escherichia coli proteins.

Detection of homocysteine and cysteine

At elevated levels, homocysteine (Hcy, 1) is a risk factor for cardiovascular diseases, Alzheimer's disease, neural tube defects, and osteoporosis. Both 1 and cysteine (Cys, 3) are linked to neurotoxicity. The biochemical mechanisms by which 1 and 3 are involved in disease states are relatively unclear. Herein, we describe simple methods for detecting either Hcy or Cys in the visible spectral region with the highest selectivity reported to date without using biochemical techniques or preparative separations. Simple methods and readily available reagents allow for the detection of Cys and Hcy in the range of their physiologically relevant levels. New HPLC postcolumn detection methods for biological thiols are reported. The potential biomedical relevance of the chemical mechanisms involved in the detection of 1 is described.

Catalytic conjugate additions of carbonyl anions under neutral aqueous conditions

The conjugate addition of carbonyl anions catalyzed by thiazolium salts that is fully operative under neutral aqueous conditions has been accomplished. The combination of alpha-keto carboxylates and thiazolium-derived zwitterions produces reactive carbonyl anions in a buffered protic environment that readily undergo conjugate additions to substituted alpha,beta-unsaturated 2-acyl imidazoles. The scope of the reaction has been examined and found to accommodate various alpha-keto carboxylates and beta-aryl substituted unsaturated 2-acyl imidazoles. The optimal precatalyst for this process is the commercially available thiazolium salt 5, a simple analogue of thiamin diphosphate. In this process, no benzoin products from carbonyl anion dimerization are observed. The corresponding 1,4-dicarbonyl compounds can be efficiently converted into esters and amides by way of activation of the N-methylimidazole ring via alkylation.

A novel strategy for oligosaccharide synthesis via temporarily deactivated S-thiazolyl glycosides as glycosyl acceptors

A new glycosylation strategy that allows chemoselective activation of the S-thiazolyl (STaz) moiety of a glycosyl donor over the temporarily deactivated glycosyl acceptor, bearing the same anomeric group, has been developed. This deactivation is achieved by engaging of the STaz moiety of the glycosyl acceptor into a stable palladium(II) complex. Therefore, obtained disaccharides are then released from the complex by simple ligand exchange. [reaction: see text]

Ni(II) Tol-BINAP-catalyzed enantioselective Michael reactions of beta-ketoesters and unsaturated N-acylthiazolidinethiones

The enantioselective addition of beta-ketoesters to unsaturated N-acylthiazolidinethiones catalyzed by Ni(II) Tol-BINAP Lewis acid complexes is reported. Notable features of this reaction are its operation simplicity, the obviated need for the addition of an external base, and the ease with which the adducts are converted into a range of potentially useful derivatives. In particular, the dihydropyrone adducts are versatile scaffolds for further stereoselective elaboration.

Potent 4-Arylalkyl-Substituted 3-Isothiazolol GABAA Competitive/Noncompetitive Antagonists: Synthesis and Pharmacology

The GABA(A) agonists muscimol (1), 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP, gaboxadol, 3), and the partial GABA(A) agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL, 6a) and their respective 3-isothiazolol analogues thiomuscimol (2), thio-THIP (4), and thio-4-PIOL (7a) are ligands at the GABA(A) orthosteric (recognition) site. The structure-activity relationships (SARs) between these structures are key elements of a 3D-pharmacophore model for GABA(A) agonists and competitive antagonists [Frølund, B.; Jørgensen, A. T.; Tagmose, L.; Stensbøl, T. B.; Vestergaard, H. T.; Engblom, C.; Kristiansen, U.; Sanchez, C.; Krogsgaard-Larsen, P.; Liljefors, T. J. Med. Chem. 2002, 45, 2454-2468]. Prompted by this model, we now report the synthesis and SAR of a series of analogues of 7a, in which the 4-position of the 3-isothiazolol was substituted by alkyl or bulky aromatic groups such as naphthylmethyl and diphenylalkyl groups (7b-h). The compounds have been pharmacologically characterized using receptor binding assays and two-electrode voltage-clamped Xenopus oocytes expressing alpha1beta3gamma2S- and alpha4beta3delta-containing receptors. The compounds show SARs comparable with those of 6b-h but are generally 5-15 times more potent. The 2-naphthylmethyl, the 1-bromo-2-naphthylmethyl, and the 3,3-diphenylpropyl analogues, compounds 7e, 7f, and 7h, respectively, show affinity in the low-nanomolar range (K(i) 2-10 nM). Interestingly, 7e and 7h exhibited a mixed antagonist profile consisting of a noncompetitive component in the picomolar range and a competitive component at concentrations above 1 nM. This unique profile was shown not to be due to either use dependence or kinetic effects. This antagonist profile of 7e and 7h was particularly pronounced at alpha4beta3delta-containing GABA(A) receptors, which showed three- and 10-fold selectivity for 7h and 6h, respectively.

Predicting the efficiencies of 2-mercaptobenzothiazole collectors used as chelating agents in flotation processes: a density-functional study

In recent years, several new chelating reagents have been synthesized and tested for their collecting power in sulfide and non-sulfide minerals flotation. Many researchers have indicated that chelating reagents have the advantage of offering better selectivity and specificity as flotation collectors. Therefore, density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level were performed to investigate the observed activities of 2-mercaptobenzothiazole, 6-methyl-2-mercaptobenzothiazole and 6-methoxy-2-mercaptobenzothiazole as the most popular flotation collectors. The molecular properties and activity relationships were determined by the HOMO localizations, the HOMO energies, Mulliken charges and the electrostatic potentials at the thioamide functional group, which is the key site in the forming efficiency of the collectors studied. It is concluded that these quantities can be used successfully for understanding the collecting abilities of 2-mercaptobenzothiazoles. The results obtained theoretically are consistent with the experimental data reported in the literature.

Development of novel amyloid imaging agents based upon thioflavin S

To date, small-molecule amyloid-imaging agents for in vivo detection and quantitation of amyloid deposits in Alzheimer's disease (AD) have been developed and successfully applied to human subjects. Preliminary studies have indicated that these amyloid-imaging agents were accumulated in the AD brains in a pattern that is relatively consistent with AD pathology, at least in the regions of amyloid-rich grey matter. These studies have also proven the concept that amyloid dyes, normally too hydrophilic to enter the brain, can be chemically modified to enhance brain permeability, binding affinity, as well as improve binding specificity for amyloid deposits. Related studies have suggested that structurally different agents can be developed that bind to different sites on amyloid deposits. In fact, in vivo cross-referencing studies based upon different amyloid-imaging agents may permit better characterization of AD pathology. But more importantly, novel amyloid imaging agents are required that will allow direct correlation between the results of animal models and human subjects based upon identical imaging modalities. Thus far, amyloid stains such as Congo red and thioflavin T have been extensively studied. However, another widely used amyloid dye, thioflavin S, has not been previously explored. This is in part due to the fact that thioflavin S exists as a mixture, not a pure chemical entity, albeit that the major component has been characterized. We hypothesized that neutral analogs, based upon the major component, could be developed as novel amyloid imaging agents, that exhibit complementary binding properties and pharmacokinetic profiles compatible with potential human studies.

Total Synthesis of Apratoxin A

[reaction: see text]. We have achieved a total synthesis of apratoxin A in which thiazoline formation was accomplished from the moCys containing amide 4 using PPh3(O)/Tf2O. Deprotection of the Troc and allyl ester in 17, coupling with tripeptide 3, and deprotection of the allyl ester and the Fmoc, followed by macrolactamization provided apratoxin A (1).

Spontaneity in the patellamide biosynthetic pathway

Post-translationally modified ribosomal peptides are unusual natural products and many have potent biological activity. The biosynthetic processes involved in their formation have been delineated for some, but the patellamides represent a unique group of these metabolites with a combination of a macrocycle, small heterocycles and d-stereocentres. The genes encoding for the patellamides show very low homology to known biosynthetic genes and there appear to be no explicit genes for the macrocyclisation and epimerisation steps. Using a combination of literature data and large-scale molecular dynamics calculations with explicit solvent, we propose that the macrocyclisation and epimerisation steps are spontaneous and interdependent and a feature of the structure of the linear peptide. Our study suggests the steps in the biosynthetic route are heterocyclisation, macrocyclisation, followed by epimerisation and finally dehydrogenation. This study is presented as testable hypothesis based on literature and theoretical data to be verified by future detailed experimental investigations.

Synthesis, X-ray crystallographic analysis, and antitumor activity of N-(benzothiazole-2-yl)-1-(fluorophenyl)-O,O-dialkyl-alpha-aminophosphonates

Alpha-aminophosphonates containing benzothiazole and fluorine moiety, 4a-4m, were synthesized by Mannich-type addition in ionic liquid media with high yield and short reaction time. Their structures were established by IR, (1)H NMR, (13)C NMR, and elemental analysis. The X-ray crystallographic data of compounds 4j and 4m were provided. The newly synthesized compounds were evaluated for their anticancer activities against PC3, A431, A375, and Bcap37 cells in vitro by the MTT method. Compound 4c is highly effective against PC3 cells and moderate to A431 cells. Hence, further study is necessary to find out the potential antitumor activities.

Acidity constants of cefetamet, cefotaxime and ceftriaxone; the effect of the substituent at C3 position

Ionization constants of three cephalosporin antibiotics, cefetamet (CEF), cefotaxime (CFX) and ceftriaxone (CFTR) are determined using pH-potentiometric titrations at I=0.1 M (NaCl) and t=25 degrees C. Cefetamet and cefotaxime have three ionization groups: carboxylic, amide and aminothiazole. Besides those three, ceftriaxone possesses an hydroxytriazinone group as new and additional ionization center. In acid medium two overlapping acid-base processes are occurring with acidity constants being: pK1 2.93 (COOH) and pK2 3.07 (aminothiazole) for cefetamet, and pK1 2.21 (COOH) and pK2 3.15 (aminothiazole) for cefotaxime. In the case of ceftriaxone the situation is even more complicated, three overlapping processes coexist with pK1 2.37 (COOH), pK2 3.03 (aminothiazole) and pK3 4.21 (hydroxytriazinone). Protolysis of amide group is happening in the alkaline medium as completely separated process from those in acid medium. The acidity constants which correspond to amide group are pK3 10.65 (CEF), pK3 10.87 (CFX) and pK4 10.74 (CFTR). The influence of the C3 substituent on the dissociation process of the neighboring ionization group, particularly carboxylic group, was considered. The differences in acidity of CEF, CFX and CFTR (pK1: 2.93, 2.21 and 2.37, respectively) are likely to be caused by the stereoelectronic properties of substituents in the beta-position to the carboxylic group due to the combined inductive, hyperconjugative and resonance effects.

Benzisothiazoles and beta-adrenoceptors: synthesis and pharmacological investigation of novel propanolamine and oxypropanolamine derivatives in isolated rat tissues

In an attempt to examine the ability of benzisothiazole-based drugs to interact with beta-adrenoceptors, a series of 1,2-benzisothiazole derivatives, which were substituted with various propanolamine or oxypropanolamine side chains in the 2 or 3 position, were synthesised and tested. The pharmacological activity of these compounds at the beta-adrenoceptors was examined using isolated rat atria and small intestinal segments, which preferentially express the beta1- and beta3-adrenoceptor-mediated responses, respectively. None of these products showed any beta-adrenoceptor agonistic activity. In contrast, the 2- and 3-substituted isopropyl, tert-butyl, benzyl, and piperonyl derivatives 2a-d and 3a-d elicited surmountable inhibition of the isoprenaline-induced chronotropic effects in the atria, suggesting competitive antagonism at the beta1-recognition site. The pA2 values revealed tert-butyl 3b and the isopropyl substituted piperonyl derivatives 3a to be the most effective. Remarkably, many of the 2-substituted propanolamines were less active than the corresponding 3-substituted oxypropanolamines. With the exception of compound 3b, none of these drugs antagonised the muscle relaxant activity of isoprenaline in the intestine, suggesting no effect on the beta3-adrenoceptors. These results confirm the ability of the benzisothiazole ring to interact with the beta-adrenoceptors, and demonstrate that 2-substitution with propanolamine or 3-substitution with oxypropanolamine groups yields compounds with preferential antagonistic activity at the cardiac beta1-adrenoceptors. The degree of antagonism depends strongly on both the nature of the substituent and its position on the benzisothiazole ring.

Unprecedented chemical structure and biomimetic synthesis of erucalexin, a phytoalexin from the wild crucifer Erucastrum gallicum

The isolation, structure determination, total synthesis and antifungal activity of erucalexin, a novel phytoalexin produced by the wild crucifer dog mustard are described. Erucalexin is a structurally unique plant alkaloid, representing the first example of a spiro[2H-indole-2,5'(4'H)-thiazol]-3-one, likely derived from a C-3-C-2 carbon migration in a 3-substituted indolyl nucleus.

Solution structures of thiopeptide antibiotics

A detailed NMR study of the thiopeptide amythiamicin D establishes its solution conformation and the presence of a single intramolecular hydrogen bond involving NH13 and O28, and also provides the first evidence for self-association of thiopeptides in solution.