Semisynthetic β-Rhodomycins: A New Approach to the Synthesis of 4-O-Methyl-β-Rhodomycins

ABSTRACT

Syntheses of 4-O-methyl-β-rhodomycins are described. Glycosylation (trimethylsilyl triflate, dichloromethane-acetone 10:1, -30 °C) of 4-O-methyl-10-O-p-nitrobenzoyl-β-rhodomycinone, obtained from β-rhodomycinone (βRMN) in a 6-step synthesis, with 1-O-tert-butyl(dimethyl)silylated derivatives of 4-O-acetyl- or 4-O-p-nitrobenzoyl-2,3,6-tri-deoxy-3-trifluoroacetylamino-β-L-arabino- and lyxo-hexopyranoses or 2,6-di-O-acetyl-2,6-dideoxy-β-L-lyxo-hexopyranose afforded 7-O-α-L-glycosyl-β-rhodomycinones. Removal of the O- and N-acyl groups with 0.1M and 1M NaOH gave the 7-O-(3-amino-2,3,6-trideoxy-α-L-arabino- and lyxo-hexopyranosyl)-4-O-methyl-β-rhodomycinones and 7-O-(2,6-dideoxy-α-L-lyxo-hexopyranosyl)-4-O-methyl-β-rhodomycinone.     

Synthesis of 4″-benzyloxyimino-4″-deoxyavermectin Bla derivatives

Six new 4″-benzyloxyimino-4″-deoxyavermectin Bla derivatives were synthesized from avermectin Bla by the selective protection of C-5-hydroxy group,oxidation of C-4″-hydroxy group,and deprotection followed by reaction with O-substituted hydroxylamine hydrochlorides.Their structures were confirmed by IR,~1H NMR,~(13)C NMR and MS.Insecticidal activities of the derivatives against Phopalosiphum pseudobrassicae,Spodoptera exigua and Pluteua xylosteua were evaluated.     

Oxidation of Methyl 4,6-O-Isopropylidene-α-d-glucopyranoside as a Model Compound for Starch

Abstract

The oxidation of methyl 4,6-O-isopropylidene-α-d-glucopyranoside (1) via various routes to the dicarboxylate 2 is described. This reaction is used as a model for the oxidation of starch to dicarboxylic starch, a material with very promising properties as a cobuilder in detergents. The best oxidant found for C₂-C₃ cleavage was RuO₄, prepared in situ by oxidation of a catalytic amount of Ru^III with NaOCl.     

Synthesis of the 4-Deoxy-2-Deutero-4-Fluoro Analog of Methyl O-β-D-Galactopyranosyl-(1→6)-β-D-Galactopyranoside

ABSTRACT

Methyl 4-deoxy-4-fluoro-6-O-(β-D-galactopyranosyl)-(2-²H)-β-D-galactopyranoside was prepared by the condensation of 2,3,4,6-tetra-O-benzoyl-α-D-galactopyranosyl bromide and methyl 2-O-benzoyl-3-O-benzyl-4-deoxy-4-fluoro-(2-²H)-β-D-galactopyranoside (17), followed by deprotection. The introduction of deuterium at C-2 in an intermediate methylhexopyranoside was achieved by a double inversion, brought about by oxidation of C-2 of a derivative of methyl α-D-glucopyranoside, to give the corresponding ketone, and subsequent reduction thereof with NaBD₄, to give a derivative with the D-manno configuration (8). Inversion of the configuration at C-2 of the latter was achieved by displacement with sodium benzoate of the O-trifluoromethanesulfonyl (triflyl) group in the 2-O-triflyl derivative of 8. The resulting synthon was converted, conventionally, to methyl 2-O-benzoyl-3-O-benzyl-6-O-trityl-(2-²H)-β-D-glucopyranoside. Its conversion into the 6-O-trityl derivative of 17, unsuccessful by treatment with dimethylaminosulfur trifluoride, was readily accomplished by the displacement of the triflyl group with fluoride ion contained in an ion-exchange resin.     

Synthesis of Methyl α-D-Kijanoside

Abstract

In 1981, Mallams and coworkers reported¹ the discovery of - D-kijanose 1, a branched-chain nitro sugar, isolated from the antitumor antibiotic kijanimicin by acid hydrolysis. The structure of this unusual carbohydrate was established ^1,2 as 2,3,4,6-tetadeo xy-4 - (methoxy carbony1 amino 1-3-c-methyl - 3 -nitro - D-xylo-hexopyranose by spectroscopic and crystallographic analysis, and comparison with D-rubranitrose 2, a carbohydrate found in the antibiotic rubradirin .³Two other nitro sugars, L-evernitrose 3 and - L-decilonitrose 4⁵, have been discoveredas components of antibiotics.     

Synthesis of the 11β-hydroxymethyl-androst-4-en-3,17-dione

The 11β-hydroxymethyl-androst-4-en-3,17-dione 5 was prepared within five synthetic steps starting from the commercially available adrenosterone with an overall yield of 24%. The 11-ketosteroid 1 was subjected to a Peterson methylenation. The subsequent hydroboration/oxidation sequence in position 11 was regio- and stereoselectively conducted using the borane-methyl sulfide complex at 0 °C. The target molecule was then obtained by deprotection using in situ generated TMSI.     

Studies Towards the Total Synthesis of Methyl Isosartortuoate： The Synthesis of a Cyclic Precusor of the Diene Unit

The preparation of the key intermediate 4 of the methyl isosartortuoate is described. The macrocyclization was completed through an intramolecular [ 2,3]-Wittig ring contraction. The four necessary stereogenic carbons were established by Sharpless asymmetric AE and AD reaction.     

Synthesis of Specifically Fluorinated Methyl β-Glycosides of (1→6)-β-D-Galactooligosaccharides II. Methyl 4-Deoxy-4-fluoro-6-O-(β-D-galactopyranosyl)-β-D-galactopyranoside

Abstract

Condensation of methyl 2,3-di-O-benzyl-4-deoxy-4-fluoro-β-D-galactopyranoside with 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl bromide in the presence of mercuric cyanide in benzene afforded, in excellent yield, the β-linked product. Its deblocking, effected by hydrogenolytic cleavage of the benzyl groups followed by deacecylation or, alternatively, via a pathway where the sequence of the deblocking reactions was reversed, gave crystalline title disaccharide 10. The structures of the compounds involved in the synthesis were confirmed by C NMR spectroscopy.     

Semisynthetic 4-O-Methyl-ß-Rhodomycins: Synthesis and Structure-Activity Relationships

ABSTRACT

The synthesis of 7-O-α-L-daunosaminyl-4-O-methyl-β-rhodomycinone (3) and the determination of its cytotoxic potency compared to that of the natural 7-O-α-L-dau-nosaminyl-β-rhodomycinone (4) are described. Starting with natural β-rhodomycinone (7), trimethylsilyl protecting groups were attached to the hydroxy groups at position 7 and 10, and the 4-OH group was subsequently methylated (MeI/Cs₂CO₃), thus providing the 4-O-methyl-7, 10-bis-O-trimethylsilyl-β-rhodomycinone (10). The two TMS groups were then deblocked to give 4-O-methyl-β-rhodomycinone (12). In a 3-stage synthesis 12 was converted into 4-O-methyl-10-O-trifiuoroacetyl-ß-rhodomycinone (15) to which l, 4-bis-O-p-nitrobenzoyl-3-N-trifluoroacetyl-L-daunosamine 16 was selectively linked to afford the 7-O-α-glycoside 17. The acyl protective groups are removed by treatment with 1N NaOH to give 3.     

Synthesis and Characterization of a Novel Compound SnDy2O4

In recent years, the research on rare earth became a focus, and a lot of rare earth complex compounds with AB2O4 stoichiometry were prepared1-3. The compound SnDy2O4 is expected to spinel-type phase while it exhibits a new structure type. SnDy2O4 was prepared by the thermal decomposition of the oxalate precursor that was prepared by rheological phase reaction method. SnO(AR), Dy2O3(99.9%) and H2C2O4·2H2O are ground in molar ratio 1:1:4.1, and placed into the reaction apparatus. …     

Synthesis and Transesterification of the Complexes of Methyl 2-Methyl-3-trichlorostannylpropoinate with Benzylmethylsulfoxide

2-Methyl-3-trichlorostannylpropionate, Cl3SnCH2CH(CH3)CO2R, a novel type of mono- organotin compounds containing ester group, have received considerable attention since Hutton et al. reported their synthesis because of the variety of coordination geometry about tin atom1-4. Organotin compounds5 like organotin carboxylates or oxides were already used as transesterification catalysts, however, little attention was paid to transestrifications of 2-methyl-3-trichlorostannylpropionate complexe…     

Synthesis and Photocleaving DNA Activity of 4′-Chlorobenzene-sulfonyl Chloride-pyrrolecarboxamide Hybrid Compound

IntroductionSyntheticphotoinducedDNAcleavageagentsareoneofthefocusesofchemistryandbiology .Theappealingfea tureofphotoinducedcleavageisthattheagentsareinertwithoutirradiation .1 3 The 4′ chloroaromaticderivativesbelongtoaclassofDNAcleavageagentswhichcaninitiatetheDNAcleavageunderlightirradiationviaproductionofcarbon centeredradical.4 Distamycin ,anoligopeptidecontainingthreeN methylpyrrolerings ,whichisanatu rallyoccurringantiviralantibiotics ,isabletobindtotheDNAminorgroovepreferential…     

Phase Transfer Catalysed Synthesis of Methyl α-Bromomethylacrylate

Methyl α-bromomethylacrylate 1 is an important intermediate both as a starting material for specifically functionalized polymers and for use in general organic synthesis. As an example of the former it has been used to prepare polymeric anthraquinoid dyes¹. Synthetically, its bifunctional reactivity towards nucleophilic attack has made it useful in the preparation of both spiro² and bicyclic^3,4 ring systems. Several reports of synthetic methods leading to α-methylenelactones, having potential antitumor activity, have also been reported which use α-bromomethylacrylate as a starting point⁵.     

Synthesis of 5,4″-di-O-succinoylavermectin B1

A reaction of avermectin B₁ with succinic anhydride at ultrahigh pressure (10 kbar) gave previously unavailable 5,4″-di-O-succinoylavermectin B₁, which is of interest as potential antiparasitic agent.

     

Studies on the Model Synthesis of the Brassinolide and Dolicholide Side Chains

A stereoselective synthesis of brassinolide and dolicholide, which involves construction of the side chain enantiomers by a highly stereoselective aldol reaction of aldehyde 5 with the anion of a-silyloxy ketone 6 is described.     

Synthesis and some chemical characteristics of 4″-nitro-3,3′:4′,3″-ter-1,2,5-oxadiazol-4-amine

A convenient preparation method was developed for 4″-nitro-3,3′:4′,3″-ter-1,2,5-oxadiazol-4-amine by substituting one nitro group of 4,4″-dinitro-3,3′:4′,3″-ter-1,2,5-oxadiazole at treating with equivalent quantity of ammonia in solvents of low polarity. In the reaction of the obtained amino-nitro derivative with N- and О- nucleophiles depending on the reaction conditions and the nucleophile nature either substitution of the nitro group occurs for the nucleophile residue to form 4″-alkoxy-, azido-, hydraznyl- or mono- and dialkylamino-[3,3′;4′,3″]-ter(1,2,5-oxadiazol)-4-ylamines, or the compound suffers an intramolecular cyclization affording 7Н-tri-1,2,5-oxadiazolo[3,4-b:3′,4′-d:3″,4″-f]azepines.     

Synthesis of 4-phenyl-3,4-dihydro-β-carboline

4-Phenyl-3,4-dihydro--carboline was prepared using the Bischler—Napieralski reaction on -phenyltryptamine.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 486–487, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis of 1-Bromo-3-methoxy-4-propoxy-5-iodobenzene——A Novel Efficient Process for the Synthesis of Brominated Aromatic Compound

The reaction of aromatic carboxylic acid with oxalyl chloride gives rise to the corresponding acid chloride which without purification is treated with the sodium salt of mercaptopyridine oxide in the presence of 2,2-azo-bisisobutyronitrile (AIBN), radical initiator to give a brominated aromatic compound. After etherification and oxidation, 5-iodovaniline was converted to trisubstituted benzene carboxylic acid which give 1-bromo-3-methoxy-4-propoxy-5-iodobenzene by this new brominating process with a yield of 74%.