O-acetyl Derivatives Research Articles

New peptaibols from Mycogone cervina.

From cultures of Mycogone cervina, a mycophilic fungus growing on the fruit bodies of ascomycete Paxina acetabulum, two new peptaibols (cervinin, N-Ac-Leu-Aib-Pro-Aib-Leu-Aib-Pro-Ala-Aib-Pro-Val-red-Leu (1) and the red-Leu O-acetylated derivative 2) were isolated. The structures of 1 and 2 were elucidated by spectroscopic techniques. They exhibited weak antibacterial as well as cytotoxic activities. They are the first secondary metabolites described from M. cervina.

Remote control of enzyme selectivity: the case of stevioside and steviolbioside

The remote control of lipase PS site- and regioselectivity by substrate modification has been observed in the acetylation of stevioside ( 1 ) and steviolbioside ( 2 ): deglucosylation at position C-19 changed the acylation site of the sophorose moiety linked at C-13. In fact, while esterification of 1 gave mainly the corresponding 6″- O-acetylated derivative, acylation of 2 gave exclusively the 6′- O-monoester. A possible rationale has been suggested, based on the conformational behavior of the substrates in different simulated solvents.

A novel synthesis of acyclonucleosides via allylation of 3-[1-(phenylhydrazono)- l- threo-2,3,4-trihydroxybut-1-yl]quinoxalin-2(1 H)one

The allylation of 3-[1-(phenylhydrazono)- l -threo-2,3,4-trihydroxybut-1-yl]quinoxalin-2(1 H)one ( 1) gave, in addition to the anticipated 1- N-allyl derivative ( 2), a dehydrative cyclized product, 1- N-allyl-3-[5-(hydroxymethyl)-1-phenylpyrazol-3-yl]quinoxalin-2-one ( 4) and its isomeric O-allyl derivative 3. The O-allyl group in 3 underwent acetolysis under acetylation conditions, in addition to the acetylation of the hydroxyl group, to afford 2-acetoxy-3-[5-(acetoxymethyl)-1-phenylpyrazol-3-yl]quinoxaline ( 8) instead of the O-acetyl derivative of 3. Allylation of the tri- O-acetyl derivative of 1 caused the elimination of a molecule of acetic acid in addition to N-allylation to give 1 -N-allyl-3-[3,4-di- O-acetyl-2-deoxy-1-(phenylhydrazono)but-2-en-1-yl]quinoxalin-2-one ( 11). Hydroxylation of the allyl group gave a glycerol-1-yl acyclonucleoside which can be alternatively obtained by a displacement reaction of the tosyloxy group in 2,3- O-isopropylidene-1- O-( p-tolylsulfonyl)glycerol ( 14), followed by deisopropylidenation. 1- N-(2,3-Dibromopropyl)-3-[5-(hydroxymethyl)-1-(4-bromophenyl)pyrazol-3-yl]quinoxalin-2-one ( 15) underwent azidolysis to give a 2,3-diazido derivative. The assigned structures were based on spectral analysis. The activity of compounds 2, 4, 6, and 15 against hepatitis B virus was studied.

Synthesis and conformational analysis of the repeating units of bacterial spore peptidoglycan

Deprotection of the fully blocked disacharide allyl O-(2-amino-4,6- O-benzylidene-3- O-[( R)-1-carboxyethyl]-2-deoxy-β- d-glucopyranosyl-1′,2-lactam)-(1→4)-2-acetamido-3,6-di- O-benzyl-2-deoxy-β- d-glucopyranoside by selective de-O-allylation and parallel removal of the benzylidene and O-benzyl groups is described. The resulting β-muramyl lactam-(1→4)-GlcNAc disaccharide is characterised as the per- O-acetylated derivative by 1H and 13C NMR spectroscopy and X-ray structure analysis. Conformational analysis about glycosidic bond of repeating units of bacterial spore cortex is based on experimental data and molecular modelling.

3-Hydroquinolylquinolines and Bisquinolyl-annelated Oxepin as Unexpected Products from the Reaction of p-Benzoquinone and N-Acetyl-1,4-dihydroquinolines

4-Substituted N-acyl-1,4-dihydroquinolines (la, b) have been yielded by regioselective 4-arylation/alkylation via quinolinium intermediates. Acid-catalysed reaction of la, b with p-benzoquinone leads to unexpected 3-hydroquinolylquinolines (5a, b). The structure of compounds (5a, b) has been confirmed by spectroscopical data and additionally by formation of both O-acetyl derivatives (7a, b). Bisquinolyl-annelated oxepin (9a) was found as side product. Formation and stereochemistry of the spectroscopically characterized compound (9a) are discussed.

Catalytic Asymmetric Synthesis of O-Acetylcyanohydrins from Potassium Cyanide, Acetic Anhydride, and Aldehydes, Promoted by Chiral Salen Complexes of Titanium(IV) and Vanadium(V)

The utility of the chiral [Ti(μ-O)(salen)]2 complexes (R)- and (S)-1 (H2salen was prepared from (R,R)- or (S,S)-cyclohexane-1,2-diamine and 3,5-di(tert-butyl)-2-hydroxybenzaldehyde) as catalysts for the asymmetric addition of KCN and Ac2O to aldehydes to produce O-acetylcyanohydrins was investigated. It was shown that the complexes were active at a substrate/catalyst ratio of 100 : 1 and produced the O-protected cyanohydrins with ee in the range of 60–92% at −40°. Other complexes, [Ti2(AcO)2(μ-O)(salen)2] ((R)-4) and [Ti(CF3COO)2(salen)] ((R)-5), were prepared from (R)-1 by treatment with different amounts of Ac2O and (CF3CO)2O, and their catalytic activities were tested under the same conditions. The efficiency of (R)-4 was found to be even greater than that of (R)-1, whereas (R)-5 was inactive. The synthesis of the corresponding salen complexes of VIV and VV, [V(O)(salen)] ((R)-2) and [V(O)(salen)(H2O)] [S(O)3OEt] ((R)-3), was elaborated, and their X-ray crystal structures were determined. The efficiency of (R)-3 was sufficient to produce O-acetyl derivatives of aromatic cyanohydrins with ee in the range of 80–91% at −40°.

Calopins and Cyclocalopins − Bitter Principles fromBoletus calopus and Related Mushrooms

Boletus calopus and closely related mushrooms of the Boletus section Calopodes are characterized by their bitter taste, which is caused mainly by O-acetylcyclocalopin A (6a), a member of a series of unique δ-lactone derivatives. Besides the simple lactone calopin (1b) and its O-acetyl derivative 1a, the more complex cyclocalopins 6−12 have been isolated and their structures elucidated. Cyclocalopin D (10a) is an unprecedented α-glucoside in which the sugar residue is bound to an enolic hydroxy group. The chemical conversion of 6b into 1a established the same stereochemistry for the calopin and cyclocalopin types of metabolites. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Lewis Acid Catalyzed Synthesis of 4-Aminopyrrolo[1,2-a]quinolin-5-ol Derivatives from 2-(1-Pyrrolyl)benzaldehyde and Isocyanides

Abstract Reaction of 2-(1-pyrrolyl)benzaldehyde with isocyanides in the presence of a catalytic amount of boron trifluoride diethyl etherate was followed by treatment with acetic anhydride in pyridine to give the corresponding O-acetyl derivatives of 4-alkyl(or aryl)aminopyrrolo[1,2-a]quinolin-5-ols in moderate yields.

Movement to bark and metabolism of xylem cytokinins in stems of Lupinus angustifolius

Zeatin riboside ( 1 R=ribofuranosyl) and dihydrozeatin riboside move rapidly from the xylem to bark tissues where a complex of cytokinin metabolites is present including O-acetyl and O-methyl derivatives.

1H and 13C NMR structure determination of new sesquiterpene glycosides isolated from Pittosporum viridiflorum viridiflorum

AbstractThe acetone extract of fresh leaves of Pittosporum viridiflorum viridiflorum afforded new sesquiterpene glycosides, 4‐O‐β‐D‐glucopyranosylgermacra‐1(10),5‐diene and its 6′‐O‐acetyl and 2′‐O‐acetyl derivatives, the structures of which were elucidated by NMR methods. Copyright © 2001 John Wiley & Sons, Ltd.

Molecular and crystal structures of N-(β- d-galactopyranosyl)pyridinium bromide and its per- O-acetylated derivative

1H NMR spectroscopy and X-ray diffraction data are described for N-(2,3,4,6-tetra- O-acetyl-β- d-galactopyranosyl)pyridinium bromide and N-(β- d-galactopyranosyl)pyridinium bromide. X-ray crystallography revealed that the O-acetylated salt crystallizes with two molecules of water and one molecule of ethanol.

Asymmetric synthesis of (S)- and (R)-α-methylserine based on the chiral recyclable reagent (S)-N-(2-benzoyl-phenyl)-1-benzylpyrrolidine-2-carboxamide

Both enantiomers of α-methylserine were synthesized with the use of NiII complexes based on the chiral recyclable reagent (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide. Intermediate diastereomeric complexes were separated by crystallization of their O-acetyl derivatives.

Cu, Pt, and Pd complexes of the 3-deoxy-1,2-bis(thiosemicarbazone) derived from d-glucose

3-Deoxy- d- erythro-hexos-2-ulose bis(thiosemicarbazone) ( 1) acts as a tetradentate ligand of the N 2S 2 type which forms stable coordination complexes with metal(II) cations. The Cu(II), Pt(II), and Pd(II) chelates ( 2, 4, and 6, respectively) of 1 were synthesized and characterized by elemental analysis and NMR spectroscopy. The NMR spectra of the Pt complex ( 4) showed the coupling of H-1 and C-1, C-2 of the bis(thiosemicarbazone) with 195Pt (33.7% naturally occurring), which supports the structure proposed for the chelate. The complexes 2, 4, and 6 were acetylated to give the corresponding tri- O-acetyl derivatives 3, 5, and 7. Elimination of Cu(II) from 3 with hydrogen sulfide afforded 8, the tri- O-acetyl derivative of 1. Preliminary studies have shown antiviral activity of chelates 2, 4, and 6 against poliovirus type 1.

Preparation of sucrose heptaesters unsubstituted at the C-1 hydroxy group of the fructose moiety via selective O-desilylation

Selective O-desilylation of 6,1′,6′-tri- O- tert-butyldiphenylsilyl-2,3,4,3′,4′-penta- O-benzoylsucrose with hydrofluoric acid in acetonitrile led to the 1′- O- tert-butyldiphenylsilyl derivative (96% yield), which was further perbenzoylated and deprotected at OH-1′ with tetrabutylammonium fluoride (86%). An analogous sequence with the corresponding O-acetylated sucrose derivative and tetrabutylammonium fluoride as desilylating agent resulted in a lower yield of the C-1′ hydroxy derivative.

Electrophilic properties of patulin. Adduct structures and reaction pathways with 4-bromothiophenol and other model nucleophiles.

The mycotoxin patulin (PAT) is believed to exert its cytotoxic and chromosome-damaging effects by forming covalent adducts with essential cellular thiols. Since the chemical structures of such adducts are unknown to date, we have studied the reaction of PAT and its O-acetylated derivative with the monofunctional thiol model compound 4-bromothiophenol (BTP), which was chosen due to analytical advantages. By means of analytical and preparative high-performance liquid chromatography, 16 adducts of PAT and 3 adducts of acetyl-PAT were isolated and their chemical structures elucidated by (1)H and (13)C NMR, IR, and UV spectroscopy. Time course studies and analysis of daughter product formation from isolated intermediate adducts led to a detailed scheme for the reaction of PAT with BTP. The structures of adducts of PAT formed with other model nucleophiles, e. g., the aliphatic thiol 2-mercaptoethanol and the aromatic amine 4-bromoaniline, were also elucidated and found to corroborate the reaction scheme. In addition, one further reaction pathway was observed with 2-mercaptoethanol, which appears to be independent from those found for BTP. Our study with model nucleophiles provides insights into the electrophilic reactivity of PAT and proved to be useful for the structure elucidation of PAT adducts with biological nucleophiles of toxicological relevance, as will be reported by Fliege and Metzler [(2000) Chem. Res. Toxicol. 13, 373-381].

6-Hydroxyluteolin-7- O-(1′′-α-rhamnoside) from Vriesea sanguinolenta Cogn. and Marchal (Bromeliaceae)

The isolation of 6-hydroxyluteolin-7- O-(1′′-α-rhamnoside) from the Central American epiphyte Vriesea sanguinolenta Cogn. and Marchal (Bromeliaceae) is described here. Its stereostructure was established by spectroscopic methods and an X-ray structure analysis of its hepta- O-acetyl derivative. This flavonoid glycoside had previously been reported from some Teucrium species (Labiatae), yet without sufficient physical data and spectroscopic evidence.

Synthesis of 4-cyanophenyl and 4-nitrophenyl 2-azido-2-deoxy-1,5-dithio-β- d-arabino- and -β- d-lyxopyranosides possessing antithrombotic activity

Tri- O-acetyl-5-thio- d-ribopyranosyl bromide was converted into 3,4-di- O-benzoyl-1,5-anhydro-5-thio- d- erythro-pent-1-enitol (3,4-di- O-benzoyl-5-thio- d-ribal), the azidonitration of which afforded an unstable mixture of 2-azido-3,4-di- O-benzoyl-2-deoxy-1- O-nitro-5-thio- d-pentopyranoside isomers. This was converted without separation into the corresponding 1- O-acetyl derivatives from which an α,β anomeric mixture of the 1- O-acetyl-2-azido-3,4-di- O-benzoyl-2-deoxy-5-thio- d-arabinopyranose isomers could be isolated in high yield. Glycosidation of this mixture with 4-cyano- or 4-nitrobenzenethiol, using trimethylsilyl triflate or boron trifluoride etherate, respectively, as promoters gave the corresponding β anomers exclusively. Zemplén debenzoylation afforded 4-cyanophenyl as well as 4-nitrophenyl 2-azido-2-deoxy-1,5-dithio-β- d-arabinopyranoside, respectively. When 1- O-acetyl-2-azido-3,4-di- O-benzoyl-2-deoxy-5-thio- d-lyxopyranose was used as glycosyl donor only the corresponding β anomers, i.e., 4-cyanophenyl as well as 4-nitrophenyl 2-azido-2-deoxy-1,5-dithio-β- d-lyxopyranosides, could be isolated after Zemplén debenzoylation in high yield. All four 1,5-dithioglycosides possess significant oral antithrombotic activity.

Synthesis and structure of 6-amino-2,3,6-trideoxy- d- erythro-hexono-1,6-lactam and 6-amino-3,6-dideoxy- d- xylo-hexono-1,6-lactam

Solid-state conformations of 6-amino-2,3,6-trideoxy- d- erythro-hexono-1,6-lactam ( 3a) and 6-amino-3,6-dideoxy- d- xylo-hexono-1,6-lactam ( 7a) were determined using X-ray diffraction. Conformations of the compounds 3a, 7a, and their per- O-acetyl derivatives 4,5-di- O-acetyl-6-amino-2,3,6-trideoxy- d- erythro-hexono-1,6-lactam ( 3b) and 2,4,5-tri- O-acetyl-6-amino-3,6-dideoxy- d- xylo-hexono-1,6-lactam ( 7b) in solutions were deduced from the analysis of NMR spectra using a modified Karplus equation and compared with the results of circular dichroism measurement of lactams 3a and 7a. Conformation 4 C 1,N was revealed for solid lactams 3a and 7a and for lactams 7a and 7b in solution, while lactams 3a and 3b in solution exist in the ∼1:1 equilibrium of the conformers 4 C 1,N and 1,N C 4.

Laccase-catalyzed oxidation of 1-(3,4-dimethoxyphenyl)-1-propene using ABTS as mediator

The fungal laccases catalyzed oxidation of 1-(3,4-dimethoxyphenyl)-1-propene ( 2) with dioxygen in acetate buffer (pH 4.5) producing 1-(3,4-dimethoxyphenyl)propane-1,2-diol ( 4) and its 1- O-acetyl and 2- O-acetyl derivatives 5 and 6, and 3,4-dimethoxybenzaldehyde ( 7). However, in phosphate buffer (pH 5.9), the same reaction produced only 4 and 7. When 4 was treated in the same fashion in the phosphate buffer, it was converted into 7 with more than 95 mol% yield. This, together with the formation of 5 and 6 in the acetate buffer, showed that 2 is converted into 3– 5 via 1-(3,4-dimethoxyphenyl)propane-1,2-epoxide ( 3) in the acetate buffer in the presence of ABTS. The major reaction of fungal laccase-catalyzed oxidation of 2 with dioxygen in the presence of ABTS is epoxidation of the double bond conjugated to the aromatic ring.

Down-regulation of GD3 ganglioside and its O-acetylated derivative by stable transfection with antisense vector against GD3-synthase gene expression in hamster melanoma cells: effects on cellular growth, melanogenesis, and dendricity.

The expression of gangliosides in hamster melanoma cells is closely related to cellular growth and degree of differentiation, with slow-growing, highly differentiated melanotic melanoma cells expressing GM3 and fast-growing, undifferentiated amelanotic Ab melanoma cells having a preponderance of GD3 and O-acetyl-GD3. We recently showed that down-regulation of O-acetyl-GD3 expression in hamster melanoma cells by introducing the influenza C virus O-acetylesterase cDNA into the cells resulted in induction of dendricity, with a concomitant increased expression of GD3. To examine the effect of the increased GD3 expression in the plasma membrane on the dendricity of the AbC-1 cells, we first established the cDNA coding for hamster GD3-synthase. We then targeted the sialyltransferase gene expression by the antisense knockdown experiment, and the results showed that inhibition of the expression of gangliosides GD3 and O-acetyl-GD3 induced dendricity in the hamster melanoma AbC-1 cell line. These GD3- and O-acetyl-GD3-depleted cells also demonstrated a decreased rate of cell growth, but their melanogenic potential was not affected. These results rule out the possibility that GD3 may serve as an active molecule for dendrite outgrowth in this cell line and suggest that the enhanced expression of O-acetyl-GD3 ganglioside may stimulate cellular growth and suppress certain differentiated phenotypes such as dendrite formation, but not melanogenesis, in our system.