The influence of cisplatin on the gas-phase dissociation of oligonucleotides studied by electrospray ionization tandem mass spectrometry

cis-Diamminedichloroplatinum(II) (cisplatin, DDP) is a cornerstone of anticancer therapy and has become one of the most widely used drugs for the treatment of various epithelial malignancies. The cytotoxicity of cisplatin is mainly based upon its affinity to adjacent guanines in nucleic acids, resulting in the formation of 1,2-intrastrand adducts. In this study the gas-phase dissociation of DNA- and RNA-cisplatin adducts is investigated by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). The fundamental mechanistic aspects of fragmentation are elucidated to provide the basis for the tandem mass spectrometric determination of binding motifs and binding sites of this important anticancer drug. It is shown that the binding of cisplatin to vicinal guanines drastically alters the gas-phase fragmentation behavior of oligonucleotides. The 3′-C-O bond adjacent to the GG base pair is preferentially cleaved, leading to extensive formation of the corresponding w-ion. This observation was even made for oligoribonucleotides, which usually tend to form c- and y-ions under CID conditions. The absence of complementary ions of equal abundance indicates that oligonucleotide-cisplatin adducts are following more than one dissociation pathway in the gas-phase. Several mechanisms that explain the increased cleavage of the 3′-C-O bond and the lack of the complementary a-ion are proposed. Results of additional MS/MS experiments on methylphosphonate-oligodeoxynucleotides confirm the proposed mechanisms.     

Synthesis and Anti-Hepatitis B Virus Activity of Glucosylated 2-O-Ethyluracils

Summary.  2-O-Ethyluracils were silylated with HMDS and condensed in the presence of TMS-triflate with β-D-glucose pentaacetate to give the corresponding β-nucleosides. Alternatively, these could be synthesized by nucleoside coupling of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide with the sodium salts of 2-O-ethyluracils, which were deprotected with saturated ammonia in methanol. 6′-O-Tosylate nucleoside derivatives were prepared by treating of the latter with tosyl chloride in anhydrous pyridine. The compounds thus obtained were treated with sodium azide in anhydrous DMF to afford the corresponding 6′-azido nucleoside derivatives, which can also be prepared by treatment with sodium azide in the presence of carbon tetrabromide and triphenylphosphine in anhydrous DMF. Nucleophilic displacement of the 6′-tosyloxy group by morpholine gave 6′-deoxy-6′-morpholino nucleosides. The reduction of the azido group of the 6′-azido nucleosides using triphenylphosphine in pyridine afforded the 6′-amino analogues. Glucosylated 2-O-ethyluracils showed moderate activity against HBV. E-mail: adelnassar63@hotmail.com Received September 16, 2002; accepted (revised) October 15, 2002 Published online April 24, 2003     

Ellagic acid glycosides from the stem bark of <Emphasis Type="Italic">Aphananthe aspera</Emphasis>

Five ellagic acid glycosides were isolated from Aphananthe aspera and their structures were identified as 3-O-methylellagic acid-4′-O-α-L-rhamnopyranoside (1), 3-O-methylellagic acid-4′-O-β-D-xylopyranoside (2), 3,3′-di-O-methylellagic acid-4′-O-β-D-xylopyranoside (3), 3,3′, 4-tri-O-methylellagic acid-4′-O-β-D-glucopyranoside (4), and 3,3′-di-O-methylellagic acid-4′-O-α-L-rhamnopyranoside (5) on the basis of spectroscopic analysis. Compound 1 is new, and all the compounds were isolated for the first time from the title plant. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 458–459, September–October, 2007.     

2′-O-Lysylaminohexyladenosine modified oligonucleotides

Abstract  

Development of therapeutically active oligonucleotides for sequence-specific gene knockdown relies on chemical modifications that confer high stability and target affinity and ideally enable cellular uptake. 2′-O-Lysylaminohexyluridine-containing antisense and siRNA oligonucleotides have been shown to be well suited for gene knockdown. They are highly resistant to enzymatic degradation while having good affinity for the targeted RNA strand and efficiently down-regulate their target in cell culture tumor models. The 2′-O-lysylaminohexyl modification was expanded to adenosine nucleosides. The corresponding phosphoramidite building block was prepared in a straightforward procedure comprising six steps starting from adenosine. After 2′-O-alkylation with N-(6-bromohexyl)phthalimide and removal of the N-protecting group, the protected lysine was specifically attached to the alkylamino group. Incorporation of 2′-O-lysylaminohexyladenosine nucleotides in a test sequence confirmed that the cationic chains lead only to minor duplex destabilization and do not disturb the duplex structure. Results further emphasize the advantageous properties of 2′-O-lysylaminohexyl modified oligonucleotides for therapeutic applications.     

A new cerebrogalactoside from <Emphasis Type="Italic">Juglans mandshurica</Emphasis>

A new cerebrogalactoside, Juglans cerebroside A (1), together with five known compounds, quercetin-3-O-β-D-galactopyranoside (2), myricetin-3-O-β-D-galactopyranoside (3), 2″E-quercetin-3-O-β-D-(6″″-O-[3″(4′″-hydroxyphenyl) propylene acyl]) glucopyranoside (4), gallic acid (5), and 2-methyl-1-hexadecanol (6) were isolated from the leaves of Juglans mandshurica Maxim. The structures of these compounds were determined by 1D, 2D NMR, and MS techniques.     

Ellagic acid derivatives from the stem bark of <Emphasis Type="Italic">Dipentodon sinicus</Emphasis>

Ellagic acid derivatives were isolated from Dipentodon sinicus and their structures were identified as 3,3′,4′-tri-O-methylellagic acid (1), 3,3′-di-O-methylellagic acid (2), 4,4′-di-O-methylellagic acid (3), 3,3′-di-O-methylellagic acid-4′-O-α-L-rhamnopyranoside (4), 3,3′,4′-tri-O-methylellagic acid-4′-O-β-D-glucopyranoside (5), 3,3′-di-O-methylellagic acid-4′-O-β-D-glucopyranoside (6), and ellagic acid (7). All the compounds were isolated for the first time from the title plant. Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 106–107, March–April, 2007.     

Features of photolytic transformation of [4-(2-methyl-5-t-butyl-cyclohexadiene-1,5-dion-3,4-yl)-3-methyl-6-<Emphasis Type="Italic">tert</Emphasis>-butyl-catecholato]triphenylantimony(V)

Photolysis of [4-(2-methyl-5-tert-butyl-cyclohexadiene-1,5-dion-3,4-yl)-3-methyl-6-t-butyl-catecholato] triphenylantimony(V) in toluene by irradiation with the light of wavelength 546 nm leads to excitation of the molecule of parent compound which reacts with a molecule of Ph3SbCatQ affording 4,4′-di-(3-methyl-6-tert-butyl-o-benzoquinone) and 4,4′-di[(3-methyl-6-tert-butyl-catecholato)triphenylantimony(V)]. The formed compounds react with each other returning the system into the initial state. Action of light of wavelength 313 and 405 nm on the initial reaction mixture leads to the formation of carbon monoxide, Ph3SbCatCatSbPh3 and the products of photolytic transformation of 4,4′-di(3-methyl-6-tert-butyl-o-benzoquinone).     

The synthesis ofN-acetyl-β-l-fucosamine-1-phosphate and uridine 5′-diphospho-N-acetyl-β-l-fucosamine

Uridine 5′-(2-acetamido-2,6-dideoxy-β-l-galactopyranosyl) diphosphate (uridine 5′-diphospho-N-acetyl-β-l-fucosamine) was synthesized. The key intermediate, 3,4-di-O-acetyl-2-azido-2,6-dideoxy-β-l-galactopyranosyl dibenzyl phosphate, was prepared by a previously unknown reaction of cesium dibenzyl phosphate with the corresponding α-glycosyl nitrate and was then converted into theN-acetylated glycosyl phosphate and nucleoside diphosphate sugarsvia 3,4-di-O-acetyl-2-amino-2,6-dideoxy-β-l-galactopyranosyl phosphate using mildN-acetylation andO-deacetylation as the last synthetic steps. Published inIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 1919–1923, November, 2000.     

A new stilbene glycoside from the <Emphasis Type="Italic">n</Emphasis>-butanol fraction of <Emphasis Type="Italic">Veratrum dahuricum</Emphasis>

A new stilbene glycoside, 5-methylresveratrol-3,4′-O-β-D-diglucopyranoside (1), was isolated from the n-butanol fraction of the rhizomes of Veratrum dahuricum, together with five known stilbenoids: resveratrol-3-O-β-D-glycoside (2), 4′-methylresveratrol-3-O-β-D-glycoside (3), oxyresveratrol-4′-O-β-D-glycoside (4), oxyresveratrol-3-O-β-D-glycoside (5), and oxyresveratrol-3,4′-O-β-D-diglycoside (6), and found for the first time in the investigated plant. The structures of six isolates were identified on the basis of 1D and 2D NMR data. Compounds 1–6 showed platelet aggregation inhibition, and compound 1 had an IC₅₀ value of 383.6 μM against platelet aggregation induced by AA. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 279–282, May–June, 2009.     

Regioselective Heterocyclization of 3-(Cyclohex-2′-enyl)-4-hydroxy-6-methylpyran-2-one

Summary.  Regioselective heterocyclization of 3-(cyclohex-2′-enyl)-4-hydroxy-6-methyl pyran-2-one with various reagents afforded different heterocycles. With N-iodosuccinimide in acetonitrile at 0–5°C it gave 6-methyl-9′-iodo-2′-oxabicyclo[3.3.1]nonano[3,2-c]pyran-2-one, with C₅H₅NHBr₃ or C₆H₁₂N₄HBr₃ in CHCl₃ at 0–5°C it furnished 6-methyl-9′-bromo-2′-oxabicyclo[3.3.1]nonano[3,2-c]pyran-2-one. Cold concentrated H₂SO₄ lead to 6-methyl-2′-oxabicyclo[3.3.1]nonano[3,2-c]pyran-2-one, whereas PdCl₂(PhCN)₂ in C₆H₆ at 80°C afforded 9-methyl benzofuro[3,2-c]pyran-2-one. Corresponding author. E-mail: kcm@klyuniv.ernet.in Received December 27, 2001. Accepted (revised) March 1, 2002     

Isoflavone glycosides from the bark of Amorpha fruticosa

Four known isoflavone glucosides have been isolated from the bark of Amorpha fruticosa, which is a traditional remedy plant, for the first time. They were elucidated as 3′-hydroxy-4′-methoxyisoflavone-7-O-β-D-glucopyranoside (1), 4′,6-dimethoxyisoflavone-7-O-β-D-glucopyranoside (2), 4′-methoxyisoflavone-7-O-β-D-glucopyranoside (3), and 3′,5-dihydroxy-4′-methoxyisoflavone-7-O-β-D-glucopyranoside (4), based on the UV, FT-IR, EIMS, FABMS, HREIMS, and NMR (¹H and ¹³C, DEPT, COSY, NOESY, HMQC, and HMBC) data. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 336–338, July–August, 2006.     

Azines and azoles: CXXVII. Glycosylation of 5,7-dihydro-4 H -pyrano-[2,3- d :6,5- d′ ]dipyrimidine-4,6(3 H )-dione and its 5-phenyl-substituted analog

Glycosylation of 5-phenylpyrano[2,3-d:6,5-d′]dipyrimidine-4,6-diones through the corresponding di-O-trimethylsilyl derivative with excess 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose gives a mixture of 3-mono-and 3,7-bis(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)-5-phenylpyrano[2,3-d:6,5-d′]dipyrimidines; in the reaction with equimolar amounts of the reactants, only the monoriboside is formed. Isomeric N,N′-disubstituted pyranodipyrimidines, as well as mixtures of their mono-and disubstituted derivatives can be separated by fractional crystallization. The alkylation of pyrano[2,3-d:6,5-d′]dipyrimidine-4,6-dione and its 5-phenyl-substituted derivative with 2-oxabutane-1,4-diyl diacetate provides an efficient procedure for the synthesis of acyclic analogs of glycosides based on pyrano[2,3-d:6,5-d′]dipyrimidines. Original Russian Text ? E.V. Fedorova, V.V. Kvasha, E.P. Studentsov, A.V. Moskvin, B.A. Ivin, 2007, published in Zhurnal Obshchei Khimii, 2007, Vol. 77, No. 4, pp. 630–636. For communication CXXVI, see [1].     

Two new myricetin glycosides from pine needles of <Emphasis Type="Italic">Cedrus deodara</Emphasis>

Two new myricetin glycosides, myricetin-3-O-(6″-O-E-p-coumaroyl)-α-D-glucocopyranoside (1) and 3′,5′-di-O-methylmyricetin-3-O-(6″-O-acetyl)-α-D-glucopyranoside (2), and three known flavonoids, myricetin (3), cedrin (4), and 2R,3R-dihydromyricetin (5), were isolated from the pine needles of Cedrus deodara. Their structures were elucidated on the basis of extensive spectroscopic analysis and chemical evidence.     

A new flavone glucoside from Stachys aegyptiaca

In addition to 5,7,3′-trihydroxy-6,4′-dimethoxyflavone, 5,7,3′-trihydroxy-6,8,4′-trimethoxyflavone, isoscutellarein, luteolin, and luteolin-7-O-glucoside, the methanol extract of the aerial parts of Stachys aegyptiaca yielded a new flavone identified as luteolin 3′,4′-dimethylether-7-O-β-D-glucoside on the basis of chemical and spectroscopic methods. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 444–445, September–October, 2007.     

Reaction of several resveratrol glycoside derivatives with hypochlorites in various media

The reactions of pterostilbenoside (trans-3,5-dimethoxystilben-4′-O-β-D-glucoside) and Ar–O–Tr derivatives of resveratroloside (3,5-dihydroxystilben-4′-O-β-D-glucoside) and pinostilbenoside (3-methoxy-5-hydroxystilben-4′-O-β-D-glucoside) with NaOCl and t-BuOCl in the presence of the stable nitroxyl radical TEMPO were studied in various media. It was found that the principal product of pterostilbenoside transformation was its 2,6-dichloroderivative, a part of which was oxidized to form 2,6-dichloropterostilbene glucuronide. Trityl ethers of resveratroloside and pinostilbenoside reacted with the hypochlorites to form mixtures of products.     

Stereoselective synthesis of the polar part of mycestericins E and G

5-O-(t-Butyldimethylsilyl)-3-deoxy-3-C-hydroxymethyl-1,2-O-isopropylidene-3-(methoxycarbonylamino)-α-d-xylofuranose IV has been proved to be an appropriate building block in the stereoselective synthesis of methyl (4S)-4-[(1′R)-1′-acetoxy-4′-oxobutyl]-3-benzyl-2-oxooxazolidine-4-carboxylate III representing the polar part of the naturally occurring mycestericins E and mycestericins G.     

A novel chromone-substituted trimeric dihydroflavonol from <Emphasis Type="Italic">Anogeissus pendula</Emphasis>

A new chromone-substituted dihydrotriflavonol, (2S,3S)[6-{(3S) 3″,5″-dihydroxy-6″-methoxydihydrochromone}5,3′,4′,5′-tetrahydroxy-7-methoxy-3-O-8-dihydroflavone]₂ 3-O-8[6-{(3S) 3″,5″-dihydroxy-6″methoxydihydrochromone}3,5,3′,4′,5′-pentahydroxy-7-methoxydihydroflavonol] was isolated from the leaves of Anogeissus pendula. The structure was determined by UV, ¹H NMR, ¹³C NMR, HMBC, and CD data.     

X-ray diffraction study of 1,5-bis-(4′,4′,4′-trifluoro-1′-methyl-3′-oxo-but-1′-enylamino)-3-oxapentane

Specific features of the molecular and crystal structures of 1,5-bis-(4′,4′,4′-trifluoro-1′-methyl-3′-oxo-but-1′-enylamino)-3-oxapentane are determined by single crystal XRD.     

Fragmentation of <Emphasis Type="Italic">α</Emphasis>-radical cations of arginine-containing peptides

Fragmentation pathways of peptide radical cations, M^+·, with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of Co^III(salen)-peptide complexes [salen=N,N′-ethylenebis (salicylideneiminato)]. Subsequent hydrogen abstraction from the β-carbon of the side-chain followed by C_α-C_β bond cleavage results in the loss of a neutral side chain and formation of an α-radical cation with the radical site localized on the α-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of arginine-containing α-radicals, suggesting that for these systems radical migration precedes fragmentation. In contrast, proton-driven fragmentation dominates CID spectra of α-radicals produced via the loss of the arginine side chain. Radical-driven fragmentation of large M^+· peptide radical cations is dominated by side-chain losses, formation of even-electron a-ions and odd-electron x-ions resulting from C_α-C bond cleavages, formation of odd-electron z-ions, and loss of the N-terminal residue. In contrast, charge-driven fragmentation produces even-electron y-ions and odd-electron b-ions.     

A novel compound from <Emphasis Type="Italic">Flos carthami</Emphasis> and its bioactivity

A novel compound, 4-{1′-hydroxy-1′-mercapto-1′-[1′′-2′′(N→O)-isoquinolyl]}yl-1-benzoic acid (1), together with six known compounds, 6-hydroxykaempferol-3-O-β-D-glucopyranoside (2), rutin (3), quercetin-3-O-β-D-glucopyranoside (4), kaempferol-3-O-β-D-glucopyranoside (5), cartormin (6), hydroxysafflor yellow A (7), were isolated by chromatography from the n-BuOH fraction of 50% ethanol extraction of Flos carthami. Their structures were elucidated on the basis of spectral analysis and comparison with published data. Among them, compound 1 was shown to possess a weak protective effect against cerebral ischemic damage in rats. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 339–341, May–June, 2009.