Screening of free radical scavengers from Erigeron breviscapus using on-line HPLC-ABTS/DPPH based assay and mass spectrometer detection

Erigeron breviscapus is a well-known traditional Chinese herbal medicine. In this study, on-line HPLC-ABTS/DPPH assay coupled with MS detection were applied to screen and identify the free radical scavengers in 70% methanol extracts of E. breviscapus. Using on-line HPLC-ABTS-MS and HPLC-DPPH-MS assay, 13 radical scavengers (including 4-O-caffeoylquinic acid (4-CQA) (1), 9-caffeoyl-2,7-anhydro-2-octulosonic acid (9-COA) (2), 3-caffeoyl-2,7-anhydro-3-deoxy-2-octulopyranosonic acid (3-CDOA) (3), erigeside I (4), quercetin-3-O-glucuronide (5), eriodictyol-7-O-glucuronide (6), scutellarin (7), 1,4-di-O-caffeoylquinic acid (1,4-di-CQA) (8), 3,5-di-CQA (9), 1-malonyl-3,5-di-CQA (10), erigoster B (11), 4,5-di-CQA (12) and 4,9-di-CDOA (13)) and 9 radical scavengers (including 1, 4, 7, 8, 9, 10, 11, 12 and 13) were discovered, respectively. Furthermore, the anti-oxidative activities of 4 compounds, including 7, 9, 11 and 12 were evaluated. Reverse anti-oxidative activity order of scutellarin and 3,5-di-CQA was observed in on-line HPLC-ABTS assay and on-line HPLC-DPPH assay. To validate their anti-oxidative activities, the off-line ABTS and DPPH assays were performed. Given sufficient reaction time, 3,5-di-CQA showed higher activity than scutellarin, which was consistent with the order obtained in on-line HPLC-ABTS assay. These results revealed that on-line HPLC-ABTS assay is a more sensitive method for screening and determining free radical scavengers, especially more suitable for those compounds with slower reaction kinetics.     

An aromatic amide C-glycoside and a cyclitol derivative from stem barks of Piper guineense Schum and Thonn (Piperaceae)

Two new compounds, an aromatic amide C-glycoside, 4-C-β-D-glucopyranosyl-3,5-dihydroxy-2-methoxybenzamide (1) and a cyclitol derivative, 4-O-caffeoyl-2-C-methoxycarbonyl-1-C-methyl-2,3,6-trihydroxycyclohexanecarboxylic acid (2), were isolated from the methanol soluble extract of the stem barks of Piper guineense Schum and Thonn, together with four known quinic acids derivatives including 3-O-caffeoyl-1-methylquinic acid (3), 3-O-feruloylquinic acid (4), ethyl-4-O-feruloylquinate (5), and 5-caffeoylquinic acid (6). Their structures were established on the basis of detailed spectroscopic analysis. The radical scavenging activity of the isolates were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay. Five of them were found to have significant radical scavenging activities, while compounds 2 and 3 displayed the highest activities with IC₅₀ values of 8.35 and 7.06 μM, respectively.     

Phytochemicals from the aerial parts of Ligularia thomsonii and their radical scavenging activity

Phytochemical investigation of the aerial parts of Ligularia thomsonii has led to the isolation of three new phenylpropanoid glucosides ligularoside I (1), ligularoside II (2) and ligularoside III (3) along with nine known compounds; cinnamic acid (4), 3-phenylpropanoic acid (5), 3,4,5-trihydroxybenzoic acid (6), 4-hydroxybenzoic acid (7), p-coumaric acid (8), caffeic acid (9), 3,4-dihydroxybenzoic acid (10), kaempferol 3-O-β-d-glucopyranoside (11) and 3,5-di-O-caffeoylquinic acid (12), hitherto unreported from L. thomsonii. Their chemical structures were elucidated by spectroscopic analysis and chemical transformation. All these compounds were tested for antioxidant activity using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. Among them, compounds 9, 10 and 12 showed significant antioxidant activity against DPPH radicals with IC₅₀ of 19.6, 23.3 and 8.9 μm, respectively.     

Distinguishing mammalian sialidases by inhibition kinetics with novel derivatives of 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enonic acid, an unsaturated derivative of N-acetylneuraminic acid.

Kinetic analysis of mammalian sialidases was carried out using analogs of the potent sialidase inhibitor, 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enonic+ ++ acid (1). Substitutents at C-9 in place of the terminal hydroxyl group included a, 4-azido-2-nitrophenylthio group to give 5-acetamido-2,6-anhydro-9-S-(4-azido-2-nitrophenyl)-3,5, 9-trideoxy-9-thio-D-glycero-D-galacto-non-2-enonic acid (2), and an azide group to give 5-acetamido-2,6-anhydro-9-azido-3,5,9-trideoxy-D-glycero-D-galacto-non-2 -enonic acid (3). Competitive inhibition kinetics were observed when 1,2, and 3 were tested with the lysosomal sialidase (cultured fibroblasts) and the plasma membrane sialidase (adenovirus DNA-transformed, human embryonic kidney cells), giving a Ki of about 10 microM for both enzymes with all three compounds. In contrast, only 1 was a potent inhibitor of the microsomal sialidase (rat muscle).     

Free radical scavengers and antioxidants from Tagetes mendocina

Tagetes mendocina (Asteraceae) is a medicinal plant widely used in the Andean provinces of Argentina. Preliminary assays showed free radical scavenging activity in the methanol extract of the aerial parts, measured by the decoloration of a methanolic solution of the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and scavenging of the superoxide anion. Assay-guided isolation led to 4'-hydroxyacetophenone (1), protocatechuic acid (2), syringic acid (3), patuletin (4), quercetagetin 7-O-beta-D-glucoside (5), patuletin 7-O-beta-D-glucoside (6) and axillarin 7-O-beta-D-glucoside (7) as the free radical scavengers and antioxidant compounds from Tagetes mendocina. On the basis of dry starting material, the total phenolic content of the crude drug was 3.00% with 0.372% of flavonoids. The content of compounds 1-7 in the crude drug was 0.008, 0.015, 0.010, 0.029, 0.238, 0.058 and 0.017%, respectively. Quercetagetin 7-O-beta-D-glucoside proved to be the main free radical scavenger of the extracts measured by the DPPH decoloration test as well as for quenching the superoxide anion and inhibition of lipoperoxidation in erythrocytes. In the lipid peroxidation assay the percentual inhibition was related with the number of methoxy groups in the molecule, ranging from 86% for the quercetagetin glucoside to 67% for the monomethoxylated and 31% for the dimethoxylated derivative. The compounds showed low cytotoxicity towards human lung fibroblasts with IC50 > 1 mM for compounds 1-3 and 0.24 to 0.52 mM for the flavonoids 4-7.     

Free radical scavengers from Cymbopogon citratus (DC.) stapf plants cultivated in bioreactors by the temporary immersion (TIS) principle

The biomass production of Cymbopogon citratus shoots cultivated in bioreactors according to the temporary immersion (TIS) principle was assessed under different growth conditions. The effect of gassing with CO2-enriched air, reduced immersion frequency, vessel size and culture time on total phenolic and flavonoid content and free radical scavenging effect of the methanolic extracts was measured. From the TIS-culture of C. citratus, seven compounds were isolated and identified as caffeic acid (1), chlorogenic acid (2), neochlorogenic acid (3), p-hydroxybenzoic acid (4), p-hydroxybenzoic acid 3-O-beta-D-glucoside (5), glutamic acid (6) and luteolin 6-C-fucopyranoside (7). The occurrence of compounds 1-7 and their variability in C. citratus grown under different TIS conditions was determined by HPLC. The free radical scavenging effect of the methanolic extract and compounds was measured by the discoloration of the free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). The main metabolites in 6- and 8-week-old cultures, both in 5 and 10 1 vessels, were chlorogenic acid (2) (100-113 mg%) and neochlorogenic acid (3) (80-119 mg%), while in the cultures with CO2-enriched air and reduced immersion frequency the main compound detected in the extracts was glutamic acid (6) (400 and 670 mg% for the green and white biomass and 619 and 630 mg% for the green and white biomass, respectively). The most active compounds, as free radical scavengers, in the DPPH discoloration assay were caffeic acid (1), chlorogenic acid (2), neochlorogenic acid (3) and the flavonoid luteolin 6-C-fucopyranoside (7).     

On-line identification of the constituents of Buyang Huanwu decoction in pig serum using combined HPLC-DAD-MS techniques

Buyang Huanwu decoction (BYHWD) is a widely used Chinese traditional compound medicine that has proved effective in treating cerebrovascular illnesses; however, its active substances have remained unknown. In this paper, serum chemistry and combined high-performance liquid chromatography (HPLC), photodiode-array detection and mass-spectrometry techniques were used to study the constituents of BYHWD from pig serum after oral administration. A total of 45 characteristic HPLC peaks were detected from serum containing drug. The chemical structures of nine of the peaks were tentatively elucidated as 7,3'-dihydroxy-4'-methoxyisoflavone-7-O-glucuronide (P1), 7-hydroxy-4'-methoxyisoflavone-7-O-glucuronide (P2), 7,2',4'-trihydroxy-3'-methoxyisoflavane-7-O-sulphate (P3), 3-hydroxy-9,10-dimethoxypterocarpan-3-O-glucuronide (P4), 7,2'-dihydroxy-3',4'-dimethoxyisoflavane-7-O-glucuronide (P5), 3-hydroxy-9,10-dimethoxypterocarpane-3-O-sulphate (P6), 4(1H)-quinolinone (P7 or P8), 4-hydroxyquinoline (P8 or P7) and oleic acid (P9). All of the identified peaks, with the exception of P9, were metabolites of the constituents of BYHWD in vivo.     

Protective effects of caffeoylquinic acids on the aggregation and neurotoxicity of the 42-residue amyloid β-protein

Alzheimer’s disease (AD), a neurodegenerative disorder, is characterized by aggregation of 42-mer amyloid β-protein (Aβ42). Aβ42 aggregates through β-sheet formation and induces cytotoxicity against neuronal cells. Aβ42 oligomer, an intermediate of the aggregates, causes memory loss and synaptotoxicity in AD. Inhibition of Aβ42 aggregation by small molecules is thus a promising strategy for the treatment of AD. Caffeoylquinic acid (CQA), a phenylpropanoid found widely in natural sources including foods, shows various biological activities such as anti-oxidative ability. Previously, our group reported that 3,5-di-O-caffeoylquinic acid (3,5-di-CQA) rescued the cognitive impairment in senescence-accelerated-prone mice 8. However, structure–activity relationship of CQA derivatives on the aggregation and neurotoxicity of Aβ42 remains elusive. To evaluate the anti-amyloidogenic property of CQA-related compounds for AD therapy, we examined the effect of CQA and its derivatives on the aggregation and neurotoxicity of Aβ42. In particular, 4,5-di-O-caffeoylquinic acid (4,5-di-CQA) and 3,4,5-tri-O-caffeoylquinic acid (3,4,5-tri-CQA) strongly inhibited the aggregation of Aβ42 in a dose-dependent manner. Structure–activity relationship studies suggested that the caffeoyl group in CQA is essential for the inhibitory activity. These CQAs also suppressed the transformation into β-sheet and cytotoxicity against human neuroblastoma cells of Aβ42. Furthermore, 3,4,5-tri-CQA blocked the formation of Aβ42 oligomer. These results indicate that 3,4,5-tri-CQA could be a potential agent for the prevention of AD.     

Acylated flavonoids and phenol glycosides from Veronica thymoides subsp. pseudocinerea

A new acylated flavone glucoside, 3'-hydroxyscutellarein 7-O-(6'-O-protocatechuoyl)-beta-glucopyranoside (1), and a new phenol glucoside, 3,5-dihydroxyphenethyl alcohol 3-O-beta-glucopyranoside (6) were isolated from Veronica thymoides subsp. pseudocinerea together with seven known flavone, phenol and lignan glycosides; 3'-hydroxyscutellarein 7-O-(6'-O-trans-feruloyl)-beta-glucopyranoside (2), 3'-hydroxy, 6-O-methylscutellarein 7-O-beta-glucopyranoside (3), luteolin 7-O-beta-glucopyranoside (4), isoscutellarein 7-O-(6'-O-acetyl)-beta-allopyranosyl (1' --> 2')-beta-glucopyranoside (5), 3,4-dihydroxyphenethyl alcohol 8-O-beta-glucopyranoside (7), benzyl alcohol 7-O-beta-xylopyranosyl (1" --> 2')-beta-glucopyranoside (8), and (+)-syringaresinol 4'-O-beta-glucopyranoside (9). Compounds 2, 3 and 7-9 were reported for the first time in the genus Veronica. The structures of the isolates were determined by means of spectroscopic (UV, IR, 1D and 2D NMR, HR ESI-MS) methods. Isolated compounds (1-7) exhibited potent radical scavenging activity against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical.     

Isolation and characterization of two new phenolic acids from cultured cells of Saussurea involucrata

Two new phenolic acids, 1, 5-O-dicaffeoyl-3-O-(4-maloyl)-quinic acid (1) and 3, 5-di-O-caffeoyl-1-O-(2-O-caffeoyl-4-maloyl)-quinic acid (2), were isolated from cultured cells of Saussurea involucrata. Their structures were elucidated using 2D NMR spectroscopy and MS. Further in vitro bioactive investigations demonstrated that 3, 5-di-O-caffeoyl-1-O-(2-O-caffeoyl-4-maloyl)-quinic acid (2) had significant scavenging activities against radicals 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) and 2, 2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS).     

Geranylated phenolic constituents from the fruits of Artocarpus nobilis

Chemical investigation of the combined dichloromethane and ethyl acetate extracts of the fruits of Artocarpus nobilis, furnished four new geranylated phenolic constituents, 2,4,4'-trihydroxy-3-[(2E)-5-methoxy-3,7-dimethylocta-2,6-dienyl]chalcone (4), 1-(3,4-dihydro-3,5-dihydroxy-2-methyl-2-(3-methyl-2-butenyl)-2H-1-benzopyran-6-yl-3-(4-hydroxyphenyl)-2(E)-propen-1-one (5), 8-geranyl-3',4',7-trihydroxyflavone (8), 3'-geranyl-4',5,7-trihydroxyflavanone (9), together with known related compounds, xanthoangelol (1), xanthoangelol B (2), 3-geranyl-2,3',4,4'-tetrahydroxychalcone (3), lespeol (6), 8-geranyl-4',7-dihydroxyflavanone (7), and isonymphaeol-B (10). Compounds 3, 8 and 10 showed strong antioxidant activity against DPPH radical by spectrophotometric method.     

3,4-anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose and 4,5-Anhydro-1,2-O-isopropylidene-beta-D-fructopyranose

3,4-Anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose (8) and 4,5-anhydro-1,2-O-isopropylidene-beta-D-fructopyranose (10) have been prepared by treatment of 3,5-di-O-acetyl-1,2-O- isopropylidene-4-O-toluene-p-sulfonyl-beta-D-fructopyranose with methanolic sodium methoxide. The structures of 8 and 10 were assigned by 1H and 13C NMR spectroscopy and that of 10 by X-ray crystallography; both exist in half-chair conformations. Compounds 8 and 10 interconvert in aqueous sodium hydroxide, giving a ratio of 1:2 at equilibrium. The monoacetates of 8 and 10 (5-O-acetyl-3,4-anhydro-1,2-O-isopropylidene-beta-D-tagatopyranose and 3-O-acetyl-4,5-anhydro-1,2-O-isopropylidene-beta-D-fructopyranose) undergo stereospecific epoxide ring opening in 80% acetic acid to give mainly the axial monoacetates 5-O-acetyl-1,2-O-isopropylidene-beta-D-fructopyranose and 4-O-acetyl-1,2-O-isopropylidene-beta-D-tagatopyranose, respectively.     

Oxidation of 3-C-(2-amino-2-deoxy-D-glucopyranosyl)-1-propene compounds and the structure of 3-C-(2-amino-2-deoxy-D-glucopyranosyl)-1,2-propanediol derivatives for a synthesis of 2,3-didehydro-2,7-dideoxy-N-acetylneuraminic acid

Oxidation of 5-acetamido-4,8-anhydro-1,2,3,5-tetradeoxy-D-glycero-D-ido-non-1-enitol [3-C-(2-amino-2-deoxy-beta-D-glucopyranosyl)-1-propene] was studied to search for preparative routes to aminodeoxy didehydro nonulosonic acid derivatives. Since only moderate chiral induction was observed with osmium tetroxide dihydroxylation as well as with peracid epoxidation, the catalytic asymmetric dihydroxylation conditions were applied to give the stereocontrolled formation of 1,2-propanediol derivatives. The structures of these diastereoisomeric 1,2-propanediol derivatives were determined by X-ray crystallographic analyses. The formation of diastereoisomeric 1,2-propanediols also varied with the nature of 2-substituent on the aminodoexy glycosyl moiety. Thus 5-acetamido-4,8-anhydro-3,5-dideoxy-D-erythro-L-ido-nonitol [(2S)-3-C-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-1,2-propanediol] was obtained predominantly up to 70% from 3-C-(2-acetamido-2-deoxyglycosyl)-1-propene by the use of ADmixbeta reagent. The (2S)-propanediol derivative was transformed in a five-step reaction sequence to 2,3-didehydro-2,7-dideoxy-N-acetylneuraminic acid.     

Reaction of methylated urates with 1,1-diphenyl-2-picrylhydrazyl

The kinetics of the reaction between the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and methylated urates was studied. Urates that had methyl groups on the 1,3,9, or on the 1 and 3 or 1 and 9 nitrogens reacted with DPPH 15 to 77% faster than uric acid. Urates substituted with methyl groups on the 7 nitrogen or on both the 3 and 9 nitrogens reacted with DPPH at rates that were less than 0.1 that of uric acid. 3,7,9-Trimethyluric acid and 1,3,7,9-tetramethyluric acid reacted with DPPH at barely detectable rates. DPPH reacted with uric acid, the monomethylated urates, and some of the dimethylated urates in a ratio of 2:1. DPPH reacted with other dimethylated and trimethylated urates in a ratio of 1:1. Semiempirical MNDO calculations indicate that the most stable radical of uric acid is formed by hydrogen abstraction from the 3, 7 or 9 position. The most stable species resulting from loss of a second hydrogen lack hydrogens at the 3 and 7 positions or the 7 and 9 positions. For maximum reactivity with DPPH, methylated uric acid derivatives must have a hydrogen at nitrogen 7 and one of the hydrogens at either the 3 or 9 position.     

灯盏花 chi 的克隆及其生物信息学分析

查尔酮异构酶（CHI）是调控黄酮生物合成的关键酶,分离和克隆这一酶的功能基因,对利用转基因技术进行灯盏花黄酮生物合成的调控具有重要意义。本研究采用RT-PCR和RACE技术,获得了chi cDNA全序列,GenBank登录号为GU208823.1,序列全长996 bp,开放阅读框为594 bp,编码197个氨基酸,3-Race有一个多聚腺苷酸加尾信号。应用软件预测该基因编码蛋白分子量约为21.6 kD,理论等电点为4.78。该基因编码的蛋白无跨膜结构域,其二级结构的主要构件为α-螺旋和随机卷曲。对其三级结构进行了建模,表明其结构与苜蓿chi的三级结构相似。同时根据灯盏花chi N端序列变化的特征,提出了灯盏乙素的合成可能与chi在细胞亚结构的定位及其与合成代谢相关酶形成复合酶的特异性有关。研究为利用基因工程定向改变灯盏花黄酮代谢产物奠定了基础。     

Enantioseparation properties of (1-->6)-alpha-D-glucopyranan and (1-->6)-alpha-D-mannopyranan tris(phenylcarbamate)s as chiral stationary phases in HPLC

Synthetic polysaccharides, (1-->6)-alpha-D-glucopyranan (3a) and (1-->6)-alpha-D-mannopyranan (3b), were prepared by the cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-beta-D-glucopyranose (1a) and 1,6-anhydro-2,3,4-O-6-allyl-beta-D-mannopyranose (1b), followed by the cleavage of the allyl ether linkage of 2,3,4-tri-O-allyl-(1-->6)-alpha-D-glucopyranan (2a) and 2,3,4-tri-O-allyl-(1-->6)-alpha-D-mannopyranan (2b), respectively. 2,3,4-Tris-O-(3,5-dimethylphenylcarbamoyl)- and 2,3,4-tris-O-(3,5-dichlorophenylcarbamoyl)-(1-->6)-alpha-D-glucopyranan (CSP-1 and CSP-2, respectively) and 2,3,4-tris-O-(3,5-dimethylphenylcarbamoyl)- and 2,3,4-tris-O-(3,5-dichlorophenylcarbamoyl)-(1-->6)-alpha-D-mannopyranan (CSP-3 and CSP-4, respectively) were prepared by the reaction of 3 with the corresponding 3,5-disubstituted phenylisocyanates and the chiral recognition abilities of CSP-1-4 as chiral stationary phases (CSPs) in high-performance liquid chromatography (HPLC) were evaluated. Racemic compounds such as trans-cyclopropanedicarboxylic acid dianilide (9), 1,2,2,2-tetraphenylethanol (10), flavanone (11), Tr?ger's base (12), benzoin (13), and cobalt(III) tris(acetylacetonate) (14) were efficiently resolved using CSP-1-4. For comparison among CSPs, the chiral recognition properties of the (1-->6)-alpha-D-glucopyranan CSPs were different from that of the (1-->6)-alpha-D-mannopyranan CSPs, and CSP-4 exhibited the highest chiral recognition ability among the CSPs. The resolution factors of 12 and 14 were 0.42 and 0.56 for CSP-1, 0.32 and 2.16 for CSP-2, 1.80 and 0.84 for CSP-3, and 2.31 and 8.26 for CSP-4, respectively.     

拟细羽束梗孢发酵菌丝体中自由基清除活性成分分析

用二苯基苦基苯肼(DPPH)自由基法,首次对拟细羽束梗孢(Isaria gracilioides RCEF3 279)菌丝体的不同溶剂提取物进行了自由基清除活性的定性定量分析,发现其甲醇提取物具有较强的清除自由基活性,当菌丝浓度为10 g/L时,其甲醇提取物的自由基清除率达到了92.4％±0.3％.DPPH自显影-薄层...     

Coumarin Schiff-bases: as antioxidant and possibly anti-inflammatory agents

Coumarin Schiff-bases (CSB) possessing different substituents on the 4-methyl-2-substituted phenyl imino-2H-chromene-7-ol molecule were evaluated for their in-vitro antioxidant and plausible anti-inflammatory potential. The antioxidant studies of selected CSB were carried out by determining their reducing power, OH* radical scavenging activity, scavenging of stable 2,2-diphenyl-l-picrylhydrazine (DPPH*) radical and inhibition of the polyphenol oxidase (PPO) enzyme. The assessment of possible anti-inflammatory potential was performed by trypsin inhibition assay and inhibition of beta-glucuronidase. All the CSBs under study showed significant reducing effects. The majority of the tested CSB were found to be effective scavengers of DPPH* radical with moderate to low OH* scavenging ability and significantly inhibited the activity of PPO. With few exceptions, results from the inhibition assay of trypsin and beta-glucuronidase were not encouraging, however they may be helpful in defining structure-activity relationships in further optimization of the lead molecules.     

Determination of rate constants for the reaction of hydroxyl radicals with some purines and pyrimidines using sunlight

Sunlight mediated hydroxyl radical production from aqueous ferric perchlorate at low pH has been investigated using deoxyribose-thiobarbituric acid assay. The rate of production of hydroxyl radical was found to be dependent on the time of irradiation. Hydroxyl radical scavengers can compete with deoxyribose for hydroxyl radicals produced in the system leading to a decreased yield of thiobarbituric acid chromogen. The second-order rate constants of the added scavengers can be determined using a simple competition kinetic method. The rate constants for the reaction of hydroxyl radical with a number of purine and pyrimidine derivatives were determined using this method. The rate constants obtained (1-7 x 10(9) dm(3) mol(-1) s(-1)) were found to be in good agreement with those reported using pulse radiolysis technique. The rate constants of dimethyluracil, xanthosine, amino and methyl substituted pyrimidines, cytidine monophosphate and uridine monophosphate were also determined by this method. It is proposed that sunlight mediated production of hydroxyl radical coupled with deoxyribose-thiobarbituric acid assay is a simple and efficient method for the determination of rate constants for the reaction of hydroxyl radical with a wide range of biomolecules.     

A new and efficient strategy for the synthesis of shimofuridin analogs: 2'-O-(4-O-stearoyl-alpha-L-fucopyranosyl)thymidine and -uridine

Two shimofuridin analogs: 2'-O-(4-O-stearoyl-alpha-L-fucopyranosyl)thymidine (2) and -uridine (3) have been synthesized using D-arabinose, L-fucose, thymine, uracil, and stearoyl chloride as the starting materials. The synthetic procedures involve the facile preparation of 1-(3,5-di-O-benzyl-beta-D-ribofuranosyl)thymine (9) and -uracil (10) by coupling of 1,2-anhydro-3,5-di-O-benzyl-alpha-D-ribofuranose (8) with silylated thymine and uracil, and then stereoselective formation of the 1,2-cis (alpha) interglycoside bonds through condensation of the nucleoside derivatives 9 and 10 with 2-(2,3-di-O-benzyl-4-O-stearoyl-beta-L-fucopyranosylsulfonyl) pyrimidine (18). The 1,2-anhydro-3,5-di-O-benzyl-alpha-D-ribofuranose (8) was prepared by an improved procedure from D-arabinose.