Synthesis and spectral studies of 2-alkoxystearic acid — II

Seven 2-alkoxystearic acids containing different functional groups in the O-alkyl chain and a new dehydration product were prepared by dehydrohalogenation of 2-iodostearic acid in the presence of different alcohols. Two of the alkoxyacids can be used as intermediates for the preparation of 1-O-(1′-alkyl)glycerols.     

Prenylated flavonoids from seeds of Calopogonium mucunoides

The seeds of Calopogonium mucunoides furnished 7-O-γ,γ-dimethylallyl-8-methoxy-3′,4′-dioxymethylene-isoflavone, 7-O-γ,γ-dimethylallyl-3′-hydroxy-4′-methoxyisoflavone, 7-O-γ,γ-dimethylallyl-3′,4′-dimethoxyisoflavone and 2S-di[6′',6′'-dimethylpyrano (2′',3′':7,8;2′',3′':4′,3′)]-flavanone whose structures were established by spectroscopic means involving the use of 400 MHz ¹H NMR with double irradiation and INDOR techniques.     

Three flavonoid glycosides containing acetylated allose from stachys recta

By means of ¹³C and ¹H NMR spectroscopy three flavone glycosides, obtained from Stachys recta, were identified as 7-O-(2″-O-6″′-O-acetyl-β-D-allopyranosyl-β-D-glucopyranosides) of 4′-O-methylisoscutellarein, isoscutellarein and 3′-hydroxy-4′-O-methylisoscutellarein. The latter two compounds are isolated for the first time. Only mannose and glucose have been reported previously as sugar components of flavonoids of the genus Stachys.     

The kinetic basis for age-associated changes in quercetin and genistein glucuronidation by rat liver microsomes

The dietary bioavailability of the isoflavone genistein is decreased in older rats compared to young adults. Since flavonoids are metabolized extensively by the UDP-glucuronosyltransferases (UGTs), we hypothesized that UGT flavonoid conjugating activity changes with age. The effect of age on flavonoid glucuronidation was determined using hepatic microsomes from male F344 rats. Kinetic models of UGT activity toward the flavonol quercetin and the isoflavone genistein were established using pooled hepatic microsomal fractions of rats at different ages, and glucuronidation rates were determined using individual samples. Intrinsic clearance (V_max/K_m) values in 4-, 18- and 28-month-old rats were 0.100, 0.078 and 0.087 ml/min/mg for quercetin-7-O-glucuronide; 0.138, 0.133 and 0.088 for quercetin-3′-O-glucuronide; and 0.075, 0.077 and 0.057 for quercetin-4′-O-glucuronide, respectively. While there were no differences in formation rates of total quercetin glucuronides in individual samples, the production of the primary metabolite, quercetin-7-O-glucuronide, at 30 μM quercetin concentration was increased from 3.4 and 3.1 nmol/min/mg at 4 and 18 months to 3.8 nmol/min/mg at 28 months, while quercetin-3′-O-glucuronide formation at 28 months declined by a similar degree (P≤.05). At 30 and 300 μM quercetin concentration, the rate of quercetin-4′-O-glucuronide formation peaked at 18 months at 0.9 nmol/min/mg. Intrinsic clearance values of genistein 7-O-glucuronide increased with age, in contrast to quercetin glucuronidation. Thus, the capacity for flavonoid glucuronidation by rat liver microsomes is dependent on age, UGT isoenzymes and flavonoid structure.     

Flavonoid variation in the liverwort Conocephalum conicum: Evidence for geographic races

The flavonoids of 2 samples of Conocephalum conicum gametophyte tissue have been studied, one from U.S.A. and the other from Germany. Common to both samples were vicenin-2, lucenin-2, the 7-O-glucuronides of apigenin, chrysoeriol and luteolin and the previously unknown 7-O-glucuronide 4′-O-rhamnosides of apigenin, chrysoeriol and luteolin. Additionally the German sample contained the 7,4′-di-O-glucuronides of apigenin and luteolin and a new compound, apigenin 7-O-diglucuronide 4′-O-glucuronide. The North American sample contained, additionally, luteolin 7,3′-di-O-glucuronide, luteolin 7-O-glucuronide 3′,4′-di-O-rhamnoside (a new triglycoside) and 2 further derivatives of luteolin 7-O-glucuronide. Evidence is presented for the existence of geographic faces of C. conicum and for the qualitative invariability of the flavonoid patterns with changing season or environment.     

A simple method of the preparation of 2′-O-Methyladenosine Methylation of adenosine with methyl iodide in anhydrous alkaline medium

A simple and effective method of the methylation on the 2′-O position of adenosine is described. Adenosine is treated with CH₃I in an anhydrous alkaline medium at 0°C for 4 h. The major products of this reaction are monomethylated adenosine at either the 2′-O or 3′-O position (total of 64%) and the side products are dimethylated adenosine (2′,3′-O-dimethyladenosi, 21%, and N⁶-2′-O-dimethyladenosine, 11%). The ratio of 2′-O- and 3′-O-methyladenosine has been found to be 8 to 1. Therefore, this reaction preferentially favors the synthesis of 2′-O-methyladenosine. The monomethylated adenosine is isolated from reaction mixture by a silica gel column chromatography. Then the pure 2′-O-methyladenosine can be separated by crystallization in ethanol from the mixture of 2′-O and 3′-O-methylated isomers. The overall yield of 2′-O-methyladenosine is 42%.     

Chemical constituents from Oncocalyx glabratus and their biological activities

Chemical investigation of the aerial parts of Oncocalyx glabratus resulted in the isolation of three new flavan derivatives, 5,3′,4′-trihydroxyflavan 7-O-gallate (1), 5,4′-dihydroxyflavan 7-3′-O-digallate (2) and 5,3′-dihydroxyflavan 7-4′-O-digallate (3), named oncoglabrinol A, B and C, respectively, together with four known flavonols, (+)-catechin (4), (+)-catechin-7-O-gallate (5), catechin-7-4′-O-digallate (6A) and catechin-7-3′-O-digallate (6B). The structures of the compounds were established by 1D, 2D NMR and ESI-HRMS spectral analyses. The biological activity of the compounds was tested through a series of in vitro assays designed for determining cytotoxicity, antiviral activity against hepatitis B virus, and antidiabetic activity. All compounds were found non-toxic and showed moderate anti-HBV activity. Compounds 3 and 6 showed dual PPAR agonistic activity while others were not effective.     

Biosynthesis of pterocarpan,isoflavan and coumestan metabolites of Medicago sativa: chalcone,isoflavone and isoflavanone precursors

Comparative feeding experiments in CuCl₂,- and UV-treated lucerne (Medicago sativa) seedlings have shown that 2′,4,4′-trihydroxychalcone-[carbonyl-¹⁴C] and formononetin-[Me-¹⁴C] but not 2′,4′-dihydroxy-4-methoxychalcone-[carbonyl- ¹⁴C] or daidzein-[4-¹⁴C] were incorporated into the phytoalexins demethylhomopterocarpin, sativan and vestitol, and also into 9-O-methylcoumestrol. The synthesis of 9-O-methylcoumestrol is greatly stimulated by this abiotic treatment but coumestrol production is not noticeably affected. Daidzein and the trihydroxychalcone were precursors of coumestrol. The results are interpreted in favour of a mechanism in which methylation is an integral part of the aryl migration process associated with the biosynthesisof 4′-methoxyisoflavonoids. Formononetin, 2′,7-dihydroxy-4′-methoxyisoflavone-[Me-¹⁴C], 7-hydroxy-4′-methoxyisoflavanone-[Me-¹⁴C] and 2′,7-dihydroxy-4′-methoxyisoflavanone-[Me-¹⁴C] were all excellent precursors of demethylhomopterocarpin, sativan, vestitol and 9-O-methylcoumestrol, and thus a metabolic grid may be involved in their biosynthetic origin.     

Nucleosides and Nucleotides. 139. Stereoselective Synthesis of (2′S)-2′-C-Alkyl-2′-deoxyuridines

Abstract

A synthetic method for (2′S)-2′-C-alkyl-2′-deoxyuridines (9) has been described. Catalytic hydrogenation of 1-[2-C-alkynyl-2-O-methoxalyl-3,5-O-TIPDS-β-D-arabino-pentofuranosyl]uracils (5) gave 1-[2-C-(2-alkyl)-2-O-methoxalyl-3,5-O-TIPDS-β-D-arabino-pentofuranosyl]uracils (4) as a major product, which were then subjected to the radical deoxygenation, affording (2′S)-2′-alkyl-2′-deoxy-3′,5′-O-TIPDS-uridines (7) along with a small amount of their 2′R epimers.

     

Dilignol glycosides from needles of Picea abies

(2R,3R)-2 3-Dihydro-2-(4′-hydroxy-3′-methoxyphenyl)-3-(hydroxymethyl)-7-methoxy-5-benzofuranpropanol 4′-O-β-d-glucopyranoside [dihydrodehydrodiconiferyl alcohol glucoside], (2R,3R)-2 3-dihydro-7-hydroxy-2-(4′-hydroxy-3′-methoxyphenyl)-3-(hydroxymethyl)-5-benzofuranpropanol 4′-O-β-d-glucopyranoside and 4′-O-α-l-rhamnopyranoside, 1-(4′-hydroxy-3′-methoxyphenyl)-2- [2″-hydroxy-4″-(3-hydroxypropyl)phenoxy]-1, 3-propanediol 1-O-β-d-glucopyranoside and 4′-O-β-d-xylopyranoside, 2,3-bis[(4′-hydroxy-3′-methoxyphenyl)-methyl]-1,4-butanediol 1-O-β-d-glucopyranoside [(?)-seco-isolariciresinol glucoside] and (1R,2S,3S)-1,2,3,4-tetrahydro-7-hydroxy-1-(4′-hydroxy-3′-methoxyphenyl)-6-methoxy-2 3-naphthalenedimethanol α²-O-β-d-xylopyranoside [(?)-isolariciresinol xyloside] have been isolated from needles of Picea abies and identified.     

Synthesis and evaluation against hepatitis C virus of 7-deaza analogues of 2′-C-methyl-6-O-methyl guanosine nucleoside and l-Alanine ester phosphoramidates

7-Deazapurines are known to possess broad antiviral activity, however the 2′-C-methylguanosine analogue displays poor cell permeation and limited phosphorylation, thus is not an efficient inhibitor of hepatitis C virus (HCV) replication. We previously reported the 6-O-methyl entity as a prodrug moiety to increase liphophilicity of guanine nucleosides and the ProTide approach applied to 2′-C-methyl-6-O-methylguanosine has lead to potent HCV inhibitors now in clinical trials. In this Letter, we report the synthesis and biological evaluation of 2′-C-methyl-6-O-methyl-7-deaza guanosine and ProTide derivatives. In contrast to prior studies, removal of the N-7 of the nucleobase entirely negates anti-HCV activity compared to the 2′-C-methyl-6-O-methylguanosine analogues. To understand better this significant loss of activity, enzymatic assays and molecular modeling were carried out and suggested 2′-C-methyl-6-O-methyl-7-deaza guanosine and related ProTides do not act as efficient prodrugs of the free nucleotide, in marked contrast to the case of the parent guanine analogue.     

Acetylated allose-containing flavonoid glucosides from Stachys anisochila

In continuation of our chemosystematic study of Stachys (Labiatae) we have isolated the previously reported isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (1) and 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (4) and four new allose-containing flavonoid glycosides from S. anisochila. The new glycosides are hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranside] (6) as well as the three corresponding diacetyl analogues of 1, 4 and 6, isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside], 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside] and hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside]. Extensive two-dimensional NMR studies (proton-carbon correlations, COSY experiments) allowed assignment of all ¹H NMR sugar signals and a correction of the ¹³C NMR signal assignments for C-2 and C-3 of the allose.     

A chalcone glycoside from Abies pindrow

The EtOH extract of air-dried stems of Abies pindrow yielded okanin, okanin 4′-O-β-d-glucopyranoside, butein 4′-O-β-d-glucopyranoside, 8,3′4′-trihydroxyflavanone-7-O-β-d-glucopyranoside and a new chalcone glycoside, 2′,3′,4′:3,4-pentahydroxy-chalcone 4′-(l-arabinofuranosyl-α-1→4-d-glucopyranoside-β).     

Synthesis and antibacterial activity of a series of novel 9-O-acetyl- 4′-substituted 16-membered macrolides derived from josamycin

A series of novel 9-O-acetyl-4′-substituted 16-membered macrolides derived from josamycin has been designed and synthesized by cleavage of the mycarose of josamycin and subsequent modification of the 4′-hydroxyl group. These derivatives were evaluated for their in vitro antibacterial activities against a panel of Staphylococcus aureus and Staphylococcus epidermidis. 15 (4′-O-(3-Phenylpropanoyl)-9-O-acetyl-desmycarosyl josamycin) and 16 (4′-O-butanoyl-9-O-acetyl-desmycarosyl josamycin) exhibited comparable activities to josamycin against S. aureus (MSSA) and S. epidermidis (MSSE).     

Iodine-sodium cyanoborohydride-mediated reductive ring opening of 4,6-O-benzylidene acetals of hexopyranosides

A quick, efficient and convenient method for the regiospecific reductive ring opening of 4,6-O-benzylidene acetals of O-/S-alkyl/aryl glycosides of mono- and disaccharides, leading to the exclusive formation of the corresponding 6-O-benzyl ethers, using sodium cyanoborohydride in the presence of molecular iodine, is reported. It has been observed that common protecting groups such as ethers and esters are well tolerated under the conditions studied. The reaction was proved unsuccessful when applied to a glucosamine-derived benzylidene acetal.     

The first replacement of a chlorosulphonyloxy group by chlorine at C-2 in methyl α-D-glucopyranoside and sucrose derivatives

Treatment of methyl 3-O-acetyl-4,6-O-benzylidene-α-D-glucopyranoside 2-chlorosulphate (2), 3,4,6,3′,4′,6′-hexa-O-acetylsucrose 2,1′-bis(chlorosulphate), 3,4,6,3′,4′,6′-hexa-O-acetyl-1′-O-benzoylsucrose 2-chlorosulphate, and 3,4,3′,4′-tetra-O-acetyl-6,6′-dichloro-6,6′-dideoxysucrose 2,1′-bis(chlorosulphate) with lithium chloride in hexamethylphosphoric triamide gave the corresponding chlorodeoxy-manno derivatives. Treatment of the 2-chlorosulphate 2 with such nucleophilic reagents as lithium bromide, sodium azide, sodium chloride, and sodium benzoate in hexamethylphosphoric triamide gave the 2-hydroxy compound as a major product. Selective chlorination at C-1′ was achieved when 3,4,6,3′,4′,6′-hexa-O-acetylsucrose was treated with sulphuryl chloride in a mixture of pyridine and chloroform.     

Synthesis of 4′-C-aminoalkyl-2′-O-methyl modified RNA and their biological properties

In this paper, we describe the synthesis of 4′-C-aminoalkyl-2′-O-methylnucleosides and the properties of RNAs containing these analogs. Phosphoramidites of 4′-C-aminoethyl and 4′-C-aminopropyl-2′-O-methyluridines were prepared using glucose as starting material, and RNAs containing the analogs were synthesized using the phosphoramidites. Thermal denaturation studies revealed that these nucleoside analogs decreased the thermal stabilities of double-stranded RNAs (dsRNAs). Results of NMR, molecular modeling, and CD spectra measurements suggested that 4′-C-aminoalkyl-2′-O-methyluridine adopts an C2′-endo sugar puckering in dsRNA. The 4′-C-aminoalkyl modifications in the passenger strand and the guide strand outside the seed region were well tolerated for RNAi activity of siRNAs. Single-stranded RNAs (ssRNAs) and siRNAs containing the 4′-C-aminoethyl and 4′-C-aminopropyl analogs showed high stability in buffer containing bovine serum. Thus, siRNAs containing the 4′-C-aminoethyl and 4′-C-aminopropyl analogs are good candidates for the development of therapeutic siRNA molecules.     

Megastigmane and 7,9′-dinorlignan glycosides from the tubers of Stephania kaweesakii

Two isomers of megastigmane glycosides, (6R, 9S)-blumenol C 9-O-gentibioside (2) and (6S, 9S)-blumenol C 9-O-gentiobioside (3), and a new 7,9′-dinorlignan glycoside, stepdonorlignoside (4) were isolated from the tubers of Stephania kaweesakii. The structure determinations were considered based on the physical data and spectroscopic evidence. The absolute configurations of two megastigmanes were determined for the first time. Additionally, ten known compounds were isolated: (6R, 9S)-blumenol C 9-O-β-D-glucopyranoside, (+)-isolariciresinol 3a-O-β-D-glucopyranoside, salidroside, N-trans-caffeoyltyramine, (R)-isococlaurine, (R)-isococlaurine 4′-O-β-glucopyranoside, (−)-oblongine, (+)-magnocurarine, fordianoside, and (−)-cyclanoline.     

Flavonol tetraglycosides from the leaves of Prunus cerasus and P. Avium

Four new flavonol glycosides have been identified from fresh leaves and fruits of sweet and sour cherries (Prunus avium and P. cerasus) as minor flavonoids: quercetin 3-O-rutinosyl-7,3′-O-bisglucoside; two quercetin 3-O-rutinosyl-4′-di-O-glucosides; kaempferol 3-O-rutinosyl-4′-di-O-glucoside.     

Structures of verbascoside and orobanchoside,caffeic acid sugar esters from Orobanche rapum-genistae

The complete structural elucidation of the two caffeic acid sugar esters verbascoside and orobanchoside, has been realized by ¹H and ¹³C NMR studies. It has been demonstrated that verbascoside is β-(3′,4′-dihydroxyphenyl)ethyl-O-α-L-rhamnopyranosyl(1→3)-β-D-(4-O-caffeoyl)-glucopyranoside, and orobanchoside is β-hydroxy-β-(3′,4′-dihydroxyphenyl)-ethyl-O-α-L-rhamnopyranosyl(1→2)-β-D-(4-O-caffeoyl)-glucopyranoside.