Phenolic acid glycosides from Parmentiera cereifera Seem. (Candle tree)

Two new phenolic acid glycosides, parmentins A (1) and B (2) were isolated from the methanolic extract of the leaves and stems of candle tree (Parmentiera cereifera Seem). These compounds were accompanied by a mixture of β-sitosterol and stigmasterol (3), β-sitosterol glucoside (4), isovanillic acid (5), vanillic acid (6), and p-hydroxybenzoic acid (7). The structures of the isolated compounds were determined on the basis of physical and spectroscopic analyses, including 1D and 2D NMR (¹H, ¹³C, COSY, HSQC and HMBC) and mass spectrometry (HR-ESI-MS).     

A 13c-n.m.r. study of a di- and a tri-saccharide containing the α-d-galactopyranosyl group

The ¹³C-n.m.r. spectra of methyl 4-O-α-d-galactopyranosyl-α-d-galactopyranoside (1) and methyl 4-O-[4-O-(α-d-galactopyranosyl)-β-d-galactopyranosyl]-β-d-glucopyranoside (2) in D₂O were recorded. Comparison of these spectra with the spectra of methyl α-d-galactopyranoside (4) and methyl β-lactoside (5) provided substantial confirmation of the structures of 1 and 2.     

Interactions of five- and six-membered cyclic esters with α-chymotrypsin: Kinetic evidence for covalent enzyme intermediates

Interactions of α-chymotrypsin with 2-coumaranone (I), 3,4-dihydrocoumarin (II), o-hydroxy-α-toluenesulfonic acid sultone (III), and β-o-hydroxyphenylethanesulfonic acid sultone (IV) were studied in the presence of 14% acetonitrile at pH 7.0 by means of the proflavin displacement technique and by inhibition of N-acetyl-l-tryptophan ethyl ester (ATrEE) hydrolysis. Under saturating conditions of either I, II, or III, an enzyme intermediate was shown to accumulate using either the proflavin displacement technique or the ATrEE activity assay. The intermediates have characteristics of covalent enzyme-substrate compounds and are believed to decompose simultaneously by two pathways, one to give free enzyme and hydrolyzed cyclic ester, and the other to give the original cyclic ester and free enzyme. With α-chymotrypsin and III the observed first-order rate constant for decomposition of the intermediate by the two pathways was 0.19 ± 0.04 min^?1, while the rate constant for the hydrolytic pathway alone was 0.013 ± 0.0009 min^?1. These results indicate that the covalent-like intermediate with this sultone is not only capable of reverting to starting cyclic ester but prefers this pathway over hydrolysis. Sultone IV was found to bind to enzyme; but in contrast to the behavior of esters I–III, the binding did not result in accumulation of a covalent-like intermediate.     

Eudistomidin G,a new β-carboline alkaloid from the Okinawan marine tunicate Eudistoma glaucus and structure revision of eudistomidin B

A new β-carboline alkaloid, eudistomidin G (1), has been isolated from the Okinawan marine tunicate Eudistoma glaucus, and the structure was elucidated from spectroscopic data. Furthermore, the structure of eudistomidin B (2), which has been isolated from the same tunicate, was revised from 2a to 2b by detailed analyses of spectroscopic data. Asymmetric synthesis of the revised structure (2b) of eudistomidin B (2) and its (1S,10S)-diastereomer (2c) has been accomplished with the Noyori catalytic asymmetric hydrogen-transfer reaction. The absolute configuration of eudistomidin B (2) was confirmed to be 2b possessing (1R,10S)-configuration, from comparison of the ¹H NMR data, CD spectra, [α]_D values, and HPLC analysis of 2b, 2c, and natural eudistomidin B.     

Proline-glutamate chimera’s side chain conformation directs the type of β-hairpin structure

Our aim was to study the impact of two proline chimeras, containing a glutamic acid side chain in cis- or trans-configuration, on secondary structure formation. We further investigated to what extent the configuration of the side chain contributes to the overall peptide conformation. We used a 10 residue peptide (IYSNPDGTWT) that forms a β-hairpin in water. The turn-forming proline was substituted with either a cis- or trans-proline-glutamic acid chimera, resulting in the peptides IYSNP ^{cis -E} DGTWT (P1_P ^cis-E ) and IYSNP ^{trans -E} DGTWT (P1_P ^trans-E ). We studied the conformation of the modified peptides by circular dichroism (CD) and NMR-spectroscopy, and SEC/static light scattering (SLS) analysis. NMR analysis reveals that the modified peptides maintain the β-hairpin conformation in aqueous solution. At 5 °C and pH 4.3, the peptide (P1_P ^cis-E ) was found to adopt two coexisting β-hairpin conformations (2:2 β-hairpin, and 3:5 β-hairpin). In contrast to that, the peptide (P1_P ^trans-E ) adopts a 2:2 β-hairpin that exists in equilibrium with a 4:4 β-hairpin conformation. The adoption of ordered β-hairpin structures for both modified peptides could be confirmed by CD spectroscopy, while SEC/SLS analysis showed a monomeric oligomerization state for all three investigated peptides. With the combination of several NMR methods, we were able to elucidate that even small alterations in the side chain conformation of the proline-glutamate chimera (cis or trans) can significantly influence the conformation of the adopted β-hairpin.     

Structural studies of β-hairpin peptidomimetic antibiotics that target LptD in Pseudomonas sp.

We report structural studies in aqueous solution on backbone cyclic peptides that possess potent antimicrobial activity specifically against Pseudomonas sp. The peptides target the β-barrel outer membrane protein LptD, which plays an essential role in lipopolysaccharide transport to the outer membrane. The peptide L27-11 contains a 12-residue loop (T¹W²L³K⁴K⁵R⁶R⁷W⁸K⁹K¹⁰A¹¹K¹²) linked to a DPro–LPro template. Two related peptides were also studied, one with various Lys to ornithine or diaminobutyric acid substitutions as well as a DLys⁶ (called LB-01), and another containing the same loop sequence, but linked to an LPro–DPro template (called LB-02). NMR studies and MD simulations show that L27-11 and LB-01 adopt β-hairpin structures in solution. In contrast, LB-02 is more flexible and importantly, adopts a wide variety of different backbone conformations, but not β-hairpin conformations. L27-11 and LB-01 show antimicrobial activity in the nanomolar range against Pseudomonas aeruginosa, whereas LB-02 is essentially inactive. Thus the β-hairpin structure of the peptide is important for antimicrobial activity. An alanine scan of L27-11 revealed that tryptophan side chains (W²/W⁸) displayed on opposite faces of the β-hairpin represent key groups contributing to antimicrobial activity.     

Synthesis of guanine nucleosides by fusion,and a mechanistic aspect of the reaction

N²-Acetylguanine (1) was condensed by fusion with the fully acetylated derivatives of the following sugars: β-D-ribofuranose (2), β-D-ribopyranose (3), α-D-xylopyranose (4), β-D-xylopyranose (5), α-D-glucopyranose (6), and β-D-gluco-pyranose (7). The reaction of 1 with either 2 or 3 gave a mixture of 7-β, 9-α, and 9-β isomers, whereas only the 7-β and 9-β isomers, and virtually no 9-α isomer, were obtained when 4, 5, 6, and 7 were used. When each isomeric acetylated ribofuranosylguanine was heated in the presence of an acidic catalyst, a mixture of 7-β, 9-α, and 9-β nucleosides was formed. Close examination of the product ratios showed that the ratio of 7:9 isomers remained unchanged throughout the reactions, but the anomeric nature of the 9-substituted nucleoside was dependent on the sugar used.     

Mariannamides A and B,new cyclic octapeptides isolated from Mariannaea elegans NBRC102301

Two new cyclic octapeptides, mariannamides A (1) and B (2), have been isolated from Mariannaea elegans NBRC102301, a Pinus densiflora-derived filamentous fungus. Their structures were elucidated to be cyclo-(l-Leu¹-l-Pro¹-l-Pro²-l-Leu²-l-Ile¹-l-Pro³-l-Val¹-l-Ile²) and cyclo-(l-Leu¹-l-Pro¹-l-Pro²-l-Leu²-l-Ile¹-l-Pro³-l-Val¹-l-Val²) based on spectroscopic data and Marfey’s method. Mariannamide A (1) promoted mRNA expression of sirtuin 1 (SIRT1) in C2C12 cells, a mouse skeletal muscle myoblast cell line, and showed the antimicrobial activity against Escherichia coli and Cryptococcus neoformans.     

Callyaerins A–F and H,new cytotoxic cyclic peptides from the Indonesian marine sponge Callyspongia aerizusa

Bioassay guided fractionation of the EtOAc fraction of the sponge Callyspongia aerizusa yielded seven new cytotoxic cyclic peptides callyaerins A–F (1–6) and H (8). Their structures were determined using extensive 1D (¹H, ¹³C and DEPT) and 2D (COSY, HMQC, HMBC, TOCSY, and ROESY) NMR and mass spectral (ESI and HRESI-TOF) data. All compounds were cyclic peptides containing ring systems of 5–9 amino acids and side chains of 2–5 amino acids in length. An unusual (Z)-2,3-diaminoacrylic acid unit provided the template for ring closure and afforded the linkage to the peptidic side chain which was always initiated with a proline moiety. All peptides contained three or more proline residues and the remaining residues were predominantly hydrophobic residues with all amino acids present in the l form. Callyaerins A–F (1–6) and H (8) showed biological activity in antibacterial assays and in various cytotoxicity assays employing different tumour cell-lines (L5178Y, HeLa, and PC12). Callyaerins E (5) and H (8) exhibited strong activity against the L5178Y cell line with ED₅₀ values of 0.39 and 0.48 μM, respectively. On the other hand, callyaerin A (1) showed strong inhibitory properties towards C. albicans.     

Synthesis and diazomethane-catalysed 1→2 acyl migration of the l-arabinosyl esters of N-acylamino acids

The fully benzylated α- and β-l-arabino-pyranosyl (1 and 2) and -furanosyl esters (3 and 4) of N-acetyl-d-alanine and N-tert-butoxycarbonyl-l-phenylalanine have been synthesised. Catalytic hydrogenation of 3 and 4 gave both anomers of 1-O-(N-tert-butoxycarbonyl-l-phenylalanyl)-l-arabino-pyranose (5) and -furanose (6), which were characterised as the triacetates 7 and 8, respectively. Treatment of the cis-oriented β-anomers of 5 and 6 with 0.5 equiv. of diazomethane at 0° for 1 h led to the 1→2 acyl rearrangement, with pyranose—furanose interconversion and anomerisation, to give, upon acetylation, a mixture of 1,3,4- and 1,3,5-tri-O-acetyl-2-O-(N-tert-butoxycarbonyl-l-phenylalanyl)-α,β-l-arabino-pyranose and -furanose, the structures of which were determined by ¹H- and ¹³C-n.m.r. spectroscopy. The 1→2 acyl-migration step in the l-arabino series is immediately followed by isomerisation into the four possible forms.     

Reaktionen der glucuronsäure : 7. Mitt. Oxidationen an d-glucofuranosidurono-6,3-lactonen

Methyl α-D- (1) and methyl β-D-glucofuranosidurono-6,3-lactone (5) were oxidized at C-2 or C-5, 1,2-O-isopropylidene-α-D- (10) and 1,2-O-cyclohexylidene-α-D-glucofuranurono-6,3-lactone (11) at C-5 by various methods to the corresponding D-arabino- or D-xylo-hexulofuranosiduronolactones. In contrast to the starting materials 5, 10, and 11, the 5-uloses 15, 17, and 18 do not exhibit reducing power in alkaline Cu²⁺ solutions. Methyl 5-O-benzyl-α-D- and methyl 5-O-benzyl-β-D-arabino-2-hexulofuranosidurono-6,3-lactone reduce Benedict solution at room temperature.     

Acetolysis of Leuconostoc mesenteroides NRRL B-1299 Dextran. Isolation and characterization of tetrasacharrides containing secondary linkages from the borate-insoluble fraction

Fractionation of the deacetylated acetolyzate of the borate-insoluble fraction of the dextran elaborated by Leuconostoc mesenteroides NRRL B-1299 gave five tetrasaccharide fractions, isolated after chromatography on charcoal—Celite, paper chromatography, and paper electrophoresis. Examination of partial acid hydrolyzates of the tetrasaccharide fractions and their corresponding alditols, the relation between the logarithm of their partition functions (α') and molecular size, and methylation studies, showed them to be (a) 2³-α-d-glucosyl-nigerotriose (1), (b) a mixture of 6-α-nigerotriosyl-d-glucose (2) and 6¹-α-d-glucosyl-nigerotriose (3) and/or 6²-α-d-glucosyl-nigerotriose (4), (c) a mixture of 2¹-α-nigerosyl-isomaltose (5) and 3²-α-isomaltosyl-kojibiose (6) and/or 6²-α-nigerosyl-kojibiose (7), (d) 2-α-nigerotriosyl-d-glucose (8) and (e) nigerotetraose (9).     

Synthése,conformation et méthanolyse des chlorures de 2,3,4-tri-O-chlorosulfonyl-β- et α-L-fucopyranosyle

Treatment of α-L-fucose with sulfuryl chloride at low temperature gave mainly 2,3,4-tri-O-chlorosulfonyl-β-L-fucopyranosyl chloride (1) and a small proportion of the α-anomer (2). Both compounds adopt a ¹C₄ chair conformation. Methanolysis of 1 in the presence of silver carbonate and anhydrous calcium sulfate gave methyl 2,3,4-tri-O-chlorosulfonyl-α-L-fucopyranoside (the β-anomer being only present in small proportion), further converted into methyl α-L-fucopyranoside by treatment with a basic resin and a catalytic amount of sodium iodide. Methanolysis of 1 in the presence of sodium iodide gave directly methyl α-L-fucopyranoside, in a more rapid but less stereoselective way. Methanolysis of 2 in the presence of silver carbonate is very slow and gave, after removal of the chlorosulfonyl groups, methyl β-L-fucopyranoside with a rather poor stereoselectivity.     

Syntheses stereoselectives de 1-thioglycosides

2,3,4,6-Tetra-O-acetyl-β-d-mannopyranosyl chloride (2) was obtained in 70% yield by the action of lithium chloride on 2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl bromide (1) in hexamethylphosphoric triamide. p-Nitrobenzenethiol reacted with 1 and 2 as well as with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide (9) or its β-d-chloro analog (10), giving exclusively and in good yield the corresponding p-nitrophenyl 1-thioglycosides of inverted anomeric configuration. The 1,2-cis-d-manno and -glucop-nitrophenylglycosides were likewise prepared. α-d-Glucopyranosyl 1-thio-α-d-glucopyranoside was similarly obtained by the action of the sodium salt of 1-thio-α-d-glucopyranose on the β-chloride 10 in hexamethylphosphoric triamide, or by treatment of 10 with sodium sulfide, with subsequent deacetylation. Analogous procedures allowed the preparation of β-d-mannopyranosyl 1-thio-β-d-mann opyranoside, the corresponding α,β anomer and α-d-glucopyranosyl 1-thio-α-d-mannopyranoside, starting from bromide 1, 1-thio-α-d-mannopyranose (8),and chloride 10, respectively. When acetone was used as solvent, the reaction between 1 and 8 led instead to the α,α anomer. The thio disaccharides that are interglycosidic 4-thio analogs of methyl 4-O-(β-d-galactopyranosyl)-α-d-galactopyranoside, methyl α-cellobioside, and methyl α-maltoside, respectively, were obtained by way of the peracetates of methyl 4-thio-α-d-galactopyranoside and -glucopyranoside by reaction of the corresponding thiolates with tetra-O-acetyl-α-d-galactopyranosyl bromide, bromide 9, or chloride 10, respectively, in hexamethylphosphoric triamide. These 1-thioglycosides, and (1→1)- and (1→4)-thiodisaccharides, were characterized by ¹H- and ^{1 3}C-n.m.r. spectroscopy. Correlations were established between the polarity of the sulfur atom and certain proton and carbon chemical-shifts in the 1-thioglycosides in comparison with the O-glycosyl analogs; these correlations permitted in particular the unambigous attribution of anomeric configuration.     

Development of covalent antagonists for β1- and β2-adrenergic receptors

The selective covalent tethering of ligands to a specific GPCR binding site has attracted considerable interest in structural biology, molecular pharmacology and drug design. We recently reported on a covalently binding noradrenaline analog (FAUC37) facilitating crystallization of the β₂-adrenergic receptor (β₂AR^H2.64C) in an active state. We herein present the stereospecific synthesis of covalently binding disulfide ligands based on the pharmacophores of adrenergic β₁- and β₂ receptor antagonists. Radioligand depletion experiments revealed that the disulfide-functionalized ligands were able to rapidly form a covalent bond with a specific cysteine residue of the receptor mutants β₁AR^I2.64C and β₂AR^H2.64C. The propranolol derivative (S)-1a induced nearly complete irreversible blockage of the β₂AR^H2.64C within 30 min incubation. The CGP20712A-based ligand (S)-4 showed efficient covalent blocking of the β₂AR^H2.64C at very low concentrations. The analog (S)-5a revealed extraordinary covalent cross-linking at the β₁AR^I2.64C and β₂AR^H2.64C mutant while retaining a 41-fold selectivity for the β₁AR wild type over β₂AR. These compounds may serve as valuable molecular tools for studying β₁/β₂ subtype selectivity or investigations on GPCR trafficking and dimerization.     

Structure and biological evaluation of new cyclic and acyclic laxaphycin-A type peptides

Five new laxaphycins were isolated and fully characterised from the bloom forming cyanobacteria Anabaena torulosa sampled from Moorea, French Polynesia: three acyclic laxaphycin A-type peptides, acyclolaxaphycin A (1), [des-Gly¹¹]acyclolaxaphycin A (2) and [des-(Leu¹⁰-Gly¹¹)]acyclolaxaphycin A (3), as well as two cyclic ones, [l-Val⁸]laxaphycin A (4) and [d-Val⁹]laxaphycin A (5). The absolute configuration of the amino acids, established using advanced Marfey’s analysis for compounds 2–5, highlights a conserved stereochemistry at the Cα carbons of the peptide ring that is characteristic of this family. To the best of our knowledge, this is the first report of acyclic analogues within the laxaphycin A-type peptides. Whether these linear laxaphycins with the aliphatic β-amino acid on the N-terminal are biosynthetic precursors or compounds obtained after enzymatic hydrolysis of the macrocycle is discussed. Biological evaluation of the new compounds together with the already known laxaphycin A shows that [l-Val⁸]laxaphycin A, [d-Val⁹]laxaphycin A and [des-Gly¹¹]acyclolaxaphycin induce cellular toxicity whereas laxaphycin A and des-[(Leu¹⁰-Gly¹¹)]acyclolaxaphycin A do not affect the cellular viability. An analysis of cellular death shows that the active peptides do not induce apoptosis or necrosis but instead, involve the autophagy pathway.     

Cyclic diarylheptanoids as Na+-glucose cotransporter (SGLT) inhibitors from Acer nikoense

Two cyclic diarylheptanoids, acerogenins A (1) and B (2) have been isolated from the bark of Acer nikoense as inhibitors of Na⁺-glucose cotransporter (SGLT). Acerogenins A (1) and B (2) inhibited both isoforms, SGLT1 and SGLT2. Structure–activity relationship of acerogenin derivatives on inhibitory activity of SGLT as well as conformational analysis of 1 and 2 on the basis of J-resolved HMBC spectra and X-ray analysis were discussed.     

Proton and C-13 nuclear magnetic resonance spectra of some benzoylated aldohexoses

Chemical shifts and coupling constants of ¹H-n.m.r. spectra of the perbenzoates of α-d-glucopyranose (1), β-d-glucopyranose (2), α-d-galactopyranose (3), α-d-mannopyranose (4), β-d-mannopyranose (5), and α-d-galactofuranose (6) are reported. The ¹³C-n.m.r. chemical shifts of compounds 1-3 and 6, and of penta-O-benzoyl-β-d-galactofuranose (7) are given. Mass spectra were used to differentiate the furanoses 6 and 7 from the pyranose 3.     

Preparation,structure and spectroscopic studies of the palladium mercaptides Pd8(S-nPr)16 and Pd6(S-nPr)12

Various palladium salts react with n-propane thiol to form a mixture of the cyclic mercaptides Pd₈(S-nPr)₁₆ (I) and the known Pd₆(S-nPr)₁₂ (II). I is described as an octagonal toroid, containing a planar ring of palladium atoms, each being bridged by four mercapto groups in approximately square planar geometry. The pendant n-propyl groups radiate outward in approximately axial and equatorial orientations with respect to the ring, which was also observed in solution by ¹H and ¹³C NMR. Crystal data: space group C2/c, a=22.251(15), b=27.623(6), c=14.621(17) Å, β=116.35°(4), V=8053(4) ų. Least-squares refinement based on 3103 observed reflections led to an R value of 0.078. I and II failed to complex any appropriate guest species, as evidenced by the UV-Vis spectra. I was found to have a reversible oxidation wave at E/2= 0.77 V, and a irreversible oxidation wave of 1.09 V. II displayed two irreversible peak potentials at 0.77 and 1.09 V. In each case, the waves were one electron processes, in which the reversibility was not enhanced at low temperatures.     

Enzymatic synthesis of dimaltosyl-beta-cyclodextrin via a transglycosylation reaction using TreX, a Sulfolobus solfataricus P2 debranching enzyme

Di-O-α-maltosyl-β-cyclodextrin ((G2)₂-β-CD) was synthesized from 6-O-α-maltosyl-β-cyclodextrin (G2-β-CD) via a transglycosylation reaction catalyzed by TreX, a debranching enzyme from Sulfolobus solfataricus P2. TreX showed no activity toward glucosyl-β-CD, but a transfer product (1) was detected when the enzyme was incubated with maltosyl-β-CD, indicating specificity for a branched glucosyl chain bigger than DP2. Analysis of the structure of the transfer product (1) using MALDI-TOF/MS and isoamylase or glucoamylase treatment revealed it to be dimaltosyl-β-CD, suggesting that TreX transferred the maltosyl residue of a G2-β-CD to another molecule of G2-β-CD by forming an α-1,6-glucosidic linkage. When [¹⁴C]-maltose and maltosyl-β-CD were reacted with the enzyme, the radiogram showed no labeled dimaltosyl-β-CD; no condensation product between the two substrates was detected, indicating that the synthesis of dimaltosyl-β-CD occurred exclusively via transglycosylation of an α-1,6-glucosidic linkage. Based on the HPLC elution profile, the transfer product (1) was identified to be isomers of 6¹,6³- and 6¹,6⁴-dimaltosyl-β-CD. Inhibition studies with β-CD on the transglycosylation activity revealed that β-CD was a mixed-type inhibitor, with a K_i value of 55.6 μmol/mL. Thus, dimaltosyl-β-CD can be more efficiently synthesized by a transglycosylation reaction with TreX in the absence of β-CD. Our findings suggest that the high yield of (G2)₂-β-CD from G2-β-CD was based on both the transglycosylation action mode and elimination of the inhibitory effect of β-CD.