Polyhydroxylated pyrrolidine and pyrrolizidine alkaloids from Hyancinthoides non-scripta and Scilla campanulata

Aqueous ethanol extracts from the immature fruits and stalks of bluebell (Hyacinthoides non-scripta) were subjected to various ion-exchange column chromatographic steps to give 1,4-dideoxy-1,4-imino-D-arabinitol (1),2(R),5(R)-bis(hydroxymethyl)-3(R),4(R)-dihydroxypyrrolidine (DMDP) (2), 6-deoxy-6-C-(2,5-dihydroxyhexyl)-DMDP (3),2,5-dideoxy-2,5-imino-DL-glycero-D-manno-heptitol (homoDMDP)(4),homoDMDP-7-O-apioside (5), homoDMDP-7-O-beta-D-xylopyranoside (6), (1S*,2R*,3R*,5R*,7aR*)-1,2-dihydroxy-3,5- dihydroxymethylpyrrolizidine (7), and (1S*,2R*,3R*,5R*,6R*,7R*,7aR*)-3-hydroxymethyl-5-methyl-1,2,6,7 tetrahydroxypyrrolizidine (8). Bulbs of Scilla campanulata (Hyacinthaceae) yielded (1S*,2R*,3R*,5S*,7aR*)-1,2-dihydroxy-3,5-dihydroxy-methylpyrrol izidine (9) in addition to compounds 1-7. Compounds 3,6,7,8, and 9 are new natural products. Compound 4 is a potent competitive inhibitor with K(i) values of 1.5 microM for Caldocellum saccharolyticum beta-glucosidase and 2.2 microM for bovine liver beta-galactosidase. The 7-O-beta-D xyloside 6 was a stronger competitive inhibitor than 4 of C saccharolyticum beta-glucosidase and rat intestinal lactase, with K(i) values of 0.06 and 0.07 microM, respectively, but a weaker inhibitor of bovine liver beta-galactosidase. Furthermore, compound 4 is also a competitive inhibitor (K(i) = 1.8 microM) of porcine kidney trehalase, but 6 was inactive against this enzyme.

X-ray absorption spectroscopy of cadmium phytochelatin and model systems

Higher plants, algae and some yeasts respond to potentially toxic heavy metals such as cadmium by synthesizing phytochelatins and related cysteine-rich polypeptides. We have used X-ray absorption spectroscopy to study the nature of cadmium binding in such peptides isolated from maize (Zea mays) exposed to low levels of cadmium, and in two synthetic cadmium-peptide complexes, Cd-(gamma-Glu-Cys)3Gly and Cd-(alpha-Glu-Cys)3Gly. We have used the synthetic ions [Cd(SPh)4]2-, [Cd4(SPh)10]2- and [S4Cd10(SPh)16]4-as crystallographically defined models for the cadmium site. The Cd K-edge extended X-ray absorption fine structure (EXAFS) data, together with the Cd K, LI, LII and LIII near-edge spectra, reveal a predominantly tetrahedral coordination of cadmium by sulfur in both the phytochelatin and synthetic peptide complexes. In particular, the Cd LIII-edge lacks a peak at 3534.9 e V which was found to be prominent for oxygen- or nitrogen-coordinated species. The Cd-S distance in the phytochelatin complex is 2.54 A. The Cd K-edge EXAFS does not show any isolated, well-defined Cd-Cd interactions; however, contrary to the conclusion of previous work, their absence is not necessarily indicative of isolated cadmium-thiolate ligation. Evidence from other studies suggests that high static disorder, combined with a large vibrational component, serve to effectively wash out this contribution to the EXAFS. The sulfur K-edge, moreover, shows a low-energy feature both in the phytochelatin and in the synthetic cadmium-peptide complexes which is consistent with sulfide bound in a cluster with cadmium as found for [S4Cd10(SPh)16]4-. This feature strongly suggests the presence of a polynuclear cadmium cluster in maize phytochelatin.

Solution structure of methionine-oxidized amyloid beta-peptide (1-40). Does oxidation affect conformational switching?

The solution structure of Abeta(1-40)Met(O), the methionine-oxidized form of amyloid beta-peptide Abeta(1-40), has been investigated by CD and NMR spectroscopy. Oxidation of Met35 may have implications in the aetiology of Alzheimer's disease. Circular dichroism experiments showed that whereas Abeta(1-40) and Abeta(1-40)Met(O) both adopt essentially random coil structures in water (pH 4) at micromolar concentrations, the former aggregates within several days while the latter is stable for at least 7 days under these conditions. This remarkable difference led us to determine the solution structure of Abeta(1-40)Met(O) using 1H NMR spectroscopy. In a water-SDS micelle medium needed to solubilize both peptides at the millimolar concentrations required to measure NMR spectra, chemical shift and NOE data for Abeta(1-40)Met(O) strongly suggest the presence of a helical region between residues 16 and 24. This is supported by slow H-D exchange of amide protons in this region and by structure calculations using simulated annealing with the program XPLOR. The remainder of the structure is relatively disordered. Our previously reported NMR data for Abeta(1-40) in the same solvent shows that helices are present over residues 15-24 (helix 1) and 28-36 (helix 2). Oxidation of Met35 thus causes a local and selective disruption of helix 2. In addition to this helix-coil rearrangement in aqueous micelles, the CD data show that oxidation inhibits a coil-to-beta-sheet transition in water. These significant structural rearrangements in the C-terminal region of Abeta may be important clues to the chemistry and biology of Abeta(1-40) and Abeta(1-42).

Solution structure of amyloid beta-peptide(1-40) in a water-micelle environment. Is the membrane-spanning domain where we think it is?

The three-dimensional solution structure of the 40 residue amyloid beta-peptide, Abeta(1-40), has been determined using NMR spectroscopy at pH 5.1, in aqueous sodium dodecyl sulfate (SDS) micelles. In this environment, which simulates to some extent a water-membrane medium, the peptide is unstructured between residues 1 and 14 which are mainly polar and likely solvated by water. However, the rest of the protein adopts an alpha-helical conformation between residues 15 and 36 with a kink or hinge at 25-27. This largely hydrophobic region is likely solvated by SDS. Based on the derived structures, evidence is provided in support of a possible new location for the transmembrane domain of Abeta within the amyloid precursor protein (APP). Studies between pH 4.2 and 7.9 reveal a pH-dependent helix-coil conformational switch. At the lower pH values, where the carboxylate residues are protonated, the helix is uncharged, intact, and lipid-soluble. As the pH increases above 6. 0, part of the helical region (15-24) becomes less structured, particularly near residues E22 and D23 where deprotonation appears to facilitate unwinding of the helix. This pH-dependent unfolding to a random coil conformation precedes any tendency of this peptide to aggregate to a beta-sheet as the pH increases. The structural biology described herein for Abeta(1-40) suggests that (i) the C-terminal two-thirds of the peptide is an alpha-helix in membrane-like environments, (ii) deprotonation of two acidic amino acids in the helix promotes a helix-coil conformational transition that precedes aggregation, (iii) a mobile hinge exists in the helical region of Abeta(1-40) and this may be relevant to its membrane-inserting properties and conformational rearrangements, and (iv) the location of the transmembrane domain of amyloid precursor proteins may be different from that accepted in the literature. These results may provide new insight to the structural properties of amyloid beta-peptides of relevance to Alzheimer's disease.

Homonojirimycin isomers and N-alkylated homonojirimycins: structural and conformational basis of inhibition of glycosidases

A series of natural epimers of alpha-homonojirimycin and its N-alkylated derivatives have been prepared to investigate the contribution of the different chiral centers and conformation of the specificity and potency of inhibition of glycosidases. These epimers and N-alkylated derivatives are alpha-homonojirimycin (1), beta-homonojirimycin (2), alpha-homomannojirimycin (3), beta-homomannojirimycin (4), alpha-3,4-di-epi-homonojirimycin (5), beta-4,5-di-epi-homonojirimycin (6), N-methyl-alpha-homonojirimycin (7), and N-butyl-alpha-homonojirimycin (8). Compound 1 was a potent inhibitor of a range of alpha-glucosidases with IC50 values of 1 to 0.01 microM. Compounds 2, 3, and 4 were surprisingly inactive as inhibitors of beta-glucosidase and alpha- and beta-mannosidases but were moderately good as inhibitors of rice and some mammalian alpha-glucosidases. Compound 4 was active in the micromolar range toward all alpha-glucosidases tested. Furthermore, compound 4, which superimposes well on beta-l-fucose, was a 10-fold more effective inhibitor of alpha-l-fucosidase than 1-deoxymannojirimycin (12) and 3, with a Ki value of 0.45 microM. Only compounds 5 and 6 showed inhibitory activity toward alpha- and beta-galactosidases (6with an IC50 value of 6.4 microM against alpha-galactosidase). The high-resolution structure of 1 has been determined by X-ray diffraction and showed a chair conformation with the C1 OH (corresponding to the C6 OH in 1-deoxynojirimycin) predominantly equatorial to the piperidine ring in the crystal structure. This preferred (C1 OH equatorial) conformation was also corroborated by 1H NMR coupling constants. The coupling constants for 7 suggest the axial orientation of the C1 OH, while in 8 the C1 OH axial conformation was not observed. The C1 OH axial conformation appears to be responsible for more potent inhibition toward processing alpha-glucosidase I than alpha-glucosidase II. It has been assumed that the anti-HIV activity of alkaloidal glycosidase inhibitors results from the inhibition of processing alpha-glucosidase I, but 1, 7, and 8 were inactive against HIV-1 replication at 500 microg/mL as measured by inhibition of virus-induced cytopathogenicity in MT-4 cells. In contrast, the EC50 value for N-butyl-1-deoxynojirimycin (11), which also inhibits processing alpha-glucosidase I, was 37 microg/mL. Compound 7 has been shown to be a better inhibitor of alpha-glucosidase I than 1 and 8 both in vitro and in the cell culture system. These data imply that inhibition of HIV by glycosidase inhibitors can be due to factors other than simply inhibition of processing alpha-glucosidase I.

Nitrogen-containing furanose and pyranose analogues from Hyacinthus orientalis

Aqueous methanol extracts from the bulbs of Hyacinthusorientalis were subjected to various ion-exchange column chromatographic steps to give 2(R),5(R)-bis(hydroxymethyl)-3(R),4(R)-dihydroxypyrrolidine (DMDP) (1), 2,5-dideoxy-2,5-imino-dl-glycero-d-manno-heptitol (homoDMDP) (2), 2,5-imino-2,5,6-trideoxy-d-manno-heptitol (6-deoxy-homoDMDP) (3), 2,5-imino-2,5,6-trideoxy-d-gulo-heptitol (4), 1-deoxynojirimycin (5), 1-deoxymannojirimycin (6), alpha-homonojirimycin (7), beta-homonojirimycin (8), alpha-homomannojirimycin (9), beta-homomannojirimycin (10), and 7-O-beta-d-glucopyranosyl-alpha-homonojirimycin (MDL 25,637) (11). The structures of the new natural products 3 and 4 were determined by spectroscopic analysis, including extensive 1D and 2D NMR studies. Compound 2 was found to be a potent inhibitor of bacterial beta-glucosidase, mammalian beta-galactosidases, and mammalian trehalases, while 3 was a potent inhibitor of rice alpha-glucosidase and rat intestinal maltase. Compound 4 was observed to be a good inhibitor of alpha-l-fucosidase.

The effects of calystegines isolated from edible fruits and vegetables on mammalian liver glycosidases

The polyhydroxylated nortropane alkaloids called calystegines occur in many plants of the Convolvulaceae, Solanaceae, and Moraceae families. Certain of these alkaloids exhibit potent inhibitory activities against glycosidases and the recently demonstrated occurrence of calystegines in the leaves, skins, and sprouts of potatoes (Solanum tuberosum), and in the leaves of the eggplant (S. melongena), has raised concerns regarding the safety of these vegetables in the human diet. We have surveyed the occurrence of calystegines in edible fruits and vegetables of the families Convolvulaceae, Solanaceae, and Moraceae by GC-MS. Calystegines A3, B1, B2, and C1 were detected in all the edible fruits and vegetables tested; sweet and chili peppers, potatoes, eggplants, tomatoes, Physalis fruits, sweet potatoes, and mulberries. Calystegines B1 and C1 were potent competitive inhibitors of the bovine, human, and rat beta-glucosidase activities, with Ki values of 150, 10, and 1.9 microM, respectively for B1 and 15, 1.5, and 1 microM, respectively, for C1. Calystegine B2 was a strong competitive inhibitor of the alpha-galactosidase activity in all the livers. Human beta-xylosidase was inhibited by all four nortropanes, with calystegine C1 having a Ki of 0.13 microM. Calystegines A3 and B2 selectively inhibited the rat liver beta-glucosidase activity. The potent inhibition of mammalian beta-glucosidase and alpha-galactosidase activities in vitro raises the possibility of toxicity in humans consuming large amounts of plants that contain these compounds.

Enzymatic synthesis of the glycosides of calystegines B1 and B2 and their glycosidase inhibitory activities

Several glycosides of calystegines B1 and B2 were synthesized by use of rice alpha-glucosidase and the whole cells of Rhodotorula lactosa, and their glycosidase inhibitory activities were investigated. Incubation of mixture of calystegine B1 and maltose with rice alpha-glucosidase gave 3-O-alpha-D-glucopyranosylcalystegine B1 (2, 11.3%). An enzymatic beta-transglucosylation reaction of calystegines B1 or B2 with cellobiose using the whole cells of R. lactosa gave 3-O-beta-D-glucopyranosylcalystegine B1 (1) (0.9%) or 4-O-beta-D-glucopyranosylcalystegine B2 (3, 11.2%), respectively, while similar beta-transgalactosylation of calystegine B2 from lactose gave 4-O-beta-D-galactopyranosylcalystegine B2 (4, 10.1%). The glycosylation of calystegines B1 and B2 markedly decreased or abolished their inhibition against beta-glucosidase, alpha- or beta-galactosidase. Compound 4 however retained more or less the potency of calystegine B2 against trehalase. Interestingly, compound 1 was a noncompetitive inhibitor of rice alpha-glucosidase, with a Ki value of 0.9 +/- 0.1 microM.

Identification of a gene, pilF, required for type 4 fimbrial biogenesis and twitching motility in Pseudomonas aeruginosa

Many bacterial pathogens produce a class of surface structures called type 4 fimbriae. In Pseudomonas aeruginosa these fimbriae are responsible for adhesion and translocation across host epithelial surfaces. We have identified a novel gene involved in the complex process of type 4 fimbrial biogenesis. This gene, termed pilF, is located on SpeI fragment S at 30 min on the P. aeruginosa genomic map, which is the sixth region on the chromosome shown to contain a fimbrial-associated gene. The PilF protein has a predicted M(r) of 22402, and together with a highly homologous upstream ORF shares a chromosomal arrangement similar to that found in Haemophilus influenzae. A pilF mutant is blocked in the export/assembly of the fimbrial subunit PilA, and accumulates this protein in the membrane fraction. Complementation studies indicate that the cloned pilF gene is able to restore the expression of surface fimbriae, twitching motility and susceptibility to fimbrial-specific bacteriophage.

Calystegine B4, a novel trehalase inhibitor from Scopolia japonica

GLC-MS analysis has been developed for screening plants of the family Solanaceae for new calystegines. GLC-MS analyses of the extract of Scopolia japonica showed the presence of a new tetrahydroxy-nor-tropane alkaloid in addition to the known calystegines A3, A5, B1, B2, B3, and C1. We gave this new alkaloid the trivial name calystegine B4. The structure of calystegine B4 was determined as 1 alpha, 2 beta, 3 alpha, 4 alpha-tetrahydroxy-nor-tropane from a variety of NMR spectral data. Calystegines B1, B2, and C1 are potent competitive inhibitors with Ki values ranging from 10(-6) to 10(-7) M for almond beta-glucosidase, while calystegine B4 inhibited this enzyme in a competitive manner, with a Ki value of 7.3 microM. Calystegine B2 is also a potent inhibitor of green coffee bean alpha-galactosidase, whereas calystegine B4 exhibited no significant activity for this enzyme. Among rat intestinal glycosidases, only trehalase was potently inhibited by calystegine B4, with an IC50 value of 9.8 microM. Furthermore, calystegine B4 potently inhibited pig kidney trehalase in a competitive manner, with a Ki value of 1.2 microM, but it was almost inactive against yeast and fungal trehalases.

Functional expression of heterologous type 4 fimbriae in Pseudomonas aeruginosa

Type 4 fimbriae are surface organelles produced by a wide range of bacterial pathogens. In Pseudomonas aeruginosa they are associated with a form of surface translocation known as twitching motility and have also been implicated as the receptor for a number of fimbrial-specific bacteriophages. The infrastructural machinery required for type 4 fimbrial biogenesis appears to be conserved as heterologous subunits from other species can be expressed in P. aeruginosa. All of these studies have, until now, been performed in non-functional Pseudomonas host strains which lack twitching motility. We have constructed isogenic mutants of two commonly studied wild-type P. aeruginosa strains, PAK and PAO1, by replacing the entire pilA gene which encodes the fimbrial subunit. Fimbrial expression and twitching motility were restored by complementation in trans with either the homologous or heterologous subunits from these strains, as well as that from another type 4 fimbriate species, Dichelobacter nodosus. The expression of different subunits allowed us to investigate the precise role that the individual subunit proteins contribute to bacteriophage infection by several fimbrial-specific bacteriophages. Sensitivity to bacteriophages B3cts and D3112cts was restored by the expression of any fimbrial subunit in both PAO1 and PAK cells, indicating that infection by these bacteriophages is fimbrial dependent but not fimbrial specific. In contrast, while sensitivity to the PAK-specific bacteriophage PO4 was restored by the expression of any fimbrial subunit in PAK cells, this did not occur in PAO1 cells except when expressing the PAK subunit. In all cases, the presence of fimbriae was absolutely required to allow a productive bacteriophage infection to occur.

Fimbrial biogenesis genes of Pseudomonas aeruginosa: pilW and pilX increase the similarity of type 4 fimbriae to the GSP protein-secretion systems and pilY1 encodes a gonococcal PilC homologue

Type 4 fimbriae of Pseudomonas aeruginosa are surface filaments involved in host colonization. They mediate both attachment to host epithelial cells and flagelia-independent twitching motility. Four additional genes, pilW, pilX, pilY1 and pilY2, are located on Spel fragment E in the 5 kb intergenic region between the previously characterized genes pilV and pilE, which encode prepilin-like proteins involved in type 4 fimbrial biogenesis. The phenotypes of a transposon insertion and other mutations constructed by allelic exchange show that these genes are involved in the assembly of type 4 fimbriae. The PilW and PilX proteins are membrane located, possess the hydrophobic N-terminus characteristic of prepilin-like proteins, and appear to belong to the GspJ and GspK group of proteins that are required for protein secretion in a wide range of Gram-negative bacteria. These findings increase the similarities between the fimbrial biogenesis and the Gsp-based protein-secretion supersystems. PilY1 is a large protein with C-terminal homology to the PilC2 protein of Neisseria gonorrhoeae, thought to be a fimbrial tip-associated adhesin, and which, like PilY1, is involved in fimbrial assembly. PilY1 appears to be located in both the membrane and the external fimbrial fractions. PilY2 is a small protein that appears to play a subtle role in fimbrial biogenesis and represents a new class of protein.

Construction of improved vectors for protein production in Pseudomonas aeruginosa

We report the construction of two cloning vectors that are based on the Pseudomonas-Escherichia shuttle vector, pUCP19. The new vectors, pUCPKS and pUCPSK, contain a significantly expanded multiple cloning site (MCS) with an adjacent T7 promoter sequence. In conjunction with specifically engineered host strains encoding an inducible T7 RNA polymerase, these vectors allow the controlled production of plasmid-encoded proteins in both Escherichia coli and Pseudomonas aeruginosa to analyse the spectrum of products encoded by cloned segments of DNA. The usefulness of these vectors was demonstrated by expressing the chloramphenicol acetyltransferase (CAT)-encoding gene.

Characterization of a five-gene cluster required for the biogenesis of type 4 fimbriae in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa produces type 4 fimbriae which promote adhesion to epithelial cells and are associated with a form of surface translocation called twitching motility. Transposon mutagenesis was used to identify loci required for fimbrial assembly or function by screening for mutants that lack the spreading colony morphology characteristic of twitching motility. Six mutants were isolated that contain transposon insertions upstream of the previously characterized gene pilQ. This region contains four genes: pilM-P, which encode proteins with predicted sizes of 37.9, 22.2, 22.8 and 19.0 kDa, respectively. pilM-P appear to form an operon and to be expressed from a promoter in the intergenic region between pilM and the divergently transcribed upstream gene ponA. PilM-P were found to be required for fimbrial biogenesis by complementation studies using twitching motility and sensitivity to fimbrial-specific phage as indicators of the presence of functional fimbriae. This was confirmed by electron microscopy. PilO and PilP did not have homologues in the sequence databases, but the predicted PilN amino acid sequence displayed similarity to XpsL from Xanthamonas campestris, a protein required for protein secretion. PilP contained a hydrophobic leader sequence characteristic of lipoproteins, while PilN and PilO have long internal hydrophobic domains which may serve to localize them to the cytoplasmic membrane. PilM has shared sequence motifs with the cell division protein FtsA from Bacillus subtilis and Escherichia coli, as well as the rod-shape-determining protein MreB from E. coli. These motifs are also conserved in eukaryotic actin, in which they are involved in forming an ATPase domain. Deletion mutants of pilM and pilQ displayed a dominant negative phenotype when transformed into wild-type cells, suggesting that these genes encode proteins involved in multimeric structures.

Chiral Heterocyclic Ligands. VIII. Syntheses and Complexes of New Chelating Ligands Derived From Camphor

The syntheses of 23 new chelating ligands are described. Most of these ligands are derived from the chiral pyrazole (1) which has been linked to a variety of heterocycles , namely pyridine, pyrimidine, pyridazine, isoxazole , benzimidazole, thiophen and furan. In certain cases the parent achiral analogues have also been prepared. Preliminary studies of the coordination chemistry of these ligands with selected transition metals have been carried out. The X-ray crystal structures of palladium complexes of isoxazole- and thiophen-containing ligands have also been determined.

Chiral Heterocyclic Ligands. II. Synthesis and Palladium(II) Complexes of Chiral Pyrazolylmethyl-Pyridines and Pyrazolylmethyl-Pyrazoles

The syntheses of the pyrazolylmethylpyridines (5a-c), their chiral derivatives (7) and (8), and the chiral methylenebisindazoles (9)-(11) are reported. These bidentate ligands form stable 1 : 1 complexes with PdCl2. A single-crystal X-ray structure determination of dichloro [(4S,7R)-7,8,8-trimethyl-2-(pyridin-2-ylmethyl)-4,5,6,7-tetrahydro-4,7-methano-2H-indazole]palladium(II),(16), is also reported.

A study of stab wounds

A study was made of patients with stab wounds who attended the Accident and Emergency Department of Glasgow Royal Infirmary during 1978 and 1983. There were 318 patients. The majority, 304 (96%), were males. A total of 87 (27%) were teenagers. The most common sites of the wounds were the chest (143 patients) and the abdomen (113 patients). The features of the patients and their wounds are compared with those of a previous study carried out at the same hospital in the early 1960s (Batey & MacBain, 1967). The post-mortem reports of 25 fatal stab injury cases occurring in Glasgow between 1971 and 1978 are also reviewed. Some aspects of diagnosis, management and prevention of stab wounds are discussed.

Magnesium, potassium, sodium and calcium in post-mortem vitreous humour from humans

Levels of magnesium, potassium, sodium and calcium in post-mortem vitreous humour from human controls, fire fatalities and drowning victims have been determined. The effects of time-related internal changes, external environmental parameters and different causes of death are evaluated. Despite the positive correlation and marked increase of potassium and, to a lesser extent, of magnesium and calcium with the length of the post-mortem interval, individual biological variability severely limits the usefulness of predictions of post-mortem interval based on electrolyte metal data. At best, there is only a 2/3 chance of a prediction being within 12 h of the true value. Vitreous humour metal concentrations are affected by external influences, such as the elevated temperatures of fires which increase the rate of release of intracellular magnesium and potassium. In cases where drowning is suspected, establishment or exclusion of this cause of death is not possible on the basis of vitreous humour electrolyte metal data because of possible post-immersion diffusion across the permeable membrane of the eyeball. It appears, however, that magnesium in salt-water cases and sodium in fresh-water cases are related, albeit erratically, to the length of the immersion period.