Regioselective Methylation Research Articles

Purines. LVII. Regioselective Alkylation of N6,9-Disubstituted 8-Oxoadenines: Syntheses of the Sea Anemone Purine Caissarone and Some Positional Isomers and Analogues.

The first total synthesis of caissarone hydrochloride (1), a constituent of the sea anemone Bunodosoma caissarum, has been accomplished via a two-step route starting from N6, 9-dimethyl-8-oxoadenine (3), which is obtainable from 9-methyladenine (5) through a four-step route. The key step in the synthesis is the regioselective methylation of 3 at N(3), which has been designed on the basis of a methylation study of N6-benzyl-9-methyl-8-oxoadenine (11). Some positional isomers (19, 24, and 31) and analogues (8, 26, and 32) of 1 have also been synthesized. A 1H-NMR spectroscopic study has suggested that the free base (23) of caissarone is capable of forming a hetero-base pair (such as 41) with 2', 3', 5'-tri-O-acetylguanosine (40) in Me2SO-d6.

Lithium-N-lithiomethyldithiocarbamate: NeueN-Alkylaminomethylanion-Äquivalente II1Untersuchungen zur Anwendungsbreite der Methode: Sterisch gehinderte und aromatischeN-Methylamine

Lithium N-Lithiomethyldithiocarbamates: New N-Alkylaminomethyl Anion Equivalents II1 Investigations on the Scope of the Method: Sterically Hindered and Aromatic N-Methylamines The scope of the methyl deprotonation of secondary methylamines protected as lithiodithiocarbamates has been investigated. Deprotonation is possible with branched N-alkylmethylamines such as the cyclohexyl derivative but failed in the case of N-tert-butylmethylamine. With aromatic methylamines such as N-methylaniline regioselective methyl- as well as ortho-deprotonation is possible depending on the base used.

Chemical modification of erythromycins. IV. Synthesis and biological properties of 6-O-methylerythromycin B.

6-O-Methylerythromycin B has been synthesized from erythromycin B via regioselective methylation of the 6-hydroxyl group in 71% overall yield. This compound shows in vitro antibacterial activity comparable to erythromycins A and B and exhibits superior in vivo activity with improved pharmacokinetic properties.

ChemInform Abstract: Regioselective Methylation of C‐1 and C‐3 Positions of 1,5‐Anhydro‐4,6‐O‐benzylidene‐2‐deoxy‐3‐O‐mesyl‐D‐ribo‐hex‐1‐enitol by the Reaction with Methylmagnesium Bromide or Methyl Cuprates.

AbstractThe hexenitol (III) mentioned in the title is alkylated with the organometallic compounds (IV) to form the 1‐substituted glucals (V), (VI), and/or the 3‐substituted regioisomers (VII).

A convenient, high-yield synthesis of l-oleandrose and l-oleandral

A short, practical synthesis of l-oleandrose (2,6-dideoxy-3- O-methyl- l- arabino-hexose) from l-arabinose has been achieved. The synthesis is satisfactory for large-scale preparation of oleandrosylating intermediates, and employs dithiolane formation for protection of the aldehyde group during deoxygenation and methylation steps, and Wittig chain-extension to 2-deoxyhexose derivatives. Useful intermediates in the introduction of oleandrose glycosides into natural products, such as the 1,4-dibenzoates and the methyl glycosides, were prepared and characterized. l-Oleandral (1,5-anhydro-2,6-dideoxy-3- O-methyl- l- arabino-hex-1-enitol), another useful intermediate for glycosylation, was prepared from 3,4-di- O-acetyl- l-rhamnal by deacetylation, and regioselective methylation with stannous chloride-diazomethane.

ChemInform Abstract: Regioselective Methylation of 7,12‐Dihydropyrido(3,2‐b:5,4‐b′)diindole. Experimental and Computational Results.

AbstractThe pyrido‐fused diindole (I) is consecutively treated with KH in DMSO and methyl iodide (II) to give the 7‐methyl derivative (III).

Regioselective methylation of 7,12-dihydropyrido[3,2-b:5,4-b']diindole. Experimental and computational results

Methylation en 7 et/ou 12 par action de l'iodomethane en presence de KH dans le DMSO ou en presence de Fe(NO 3 ) 3 avec Na/NH 3

Regioselective Methylation of Epoxides Using Transition Metal Complexes

Abstract M(PPh3)4 (M= Ni, Pd, Pt) promoted regioselective methylation of 1,2-epoxy-2-methylpropane with methyl iodide affording 2,2-dimethylpropanol. In the course of the reaction, \ ranstrans-CH3MI(PPh3)2, initially formed from the reaction of M(PPh3)4 with CH3I, attacked the epoxide electrophilicly resulting regioselective cleavage of the C–O bond of the epoxide, followed by the formation of the isolable 2,2-dimethylpropoxymetal complexes.

ChemInform Abstract: Regioselective Methylation of Methyl α‐L‐Fucopyranoside with Diazomethane in the Presence of Tin(II) Chloride.

AbstractRegioselective methylation of the fucoside (I) is achieved by complexation of the cis‐3,4‐diol system with tin(II) chloride.

Regioselective methylation of methyl α- l-fucopyranoside with diazomethane in the presence of tin(II) chloride

Regioselective methylation of methyl α- l-fucopyranoside with diazomethane in the presence of tin(II) chloride

ChemInform Abstract: STUDIES ON BIOLOGICALLY ACTIVE PTERIDINES. V. SYNTHESIS OF (6S)‐5,6,7,8‐TETRAHYDRO‐1,3,5,6‐TETRAMETHYLLUMAZINE

AbstractDurch Erhitzen des Uracils (I) und des (2S)‐Propans (II) in Ethanol wird das (6S)‐Titellumazin (III) als Hauptkondensationsprodukt erhalten.

Novel regioselective C-6 and C-19 alkylation of vitamin D 3 via its sulfur-dioxide adducts

Vitamin D-sulfur dioxide adducts undergo regioselective methylation at C-6 with sodium hydride used as the base and at C-19 with lithium tetramethylpiperidide. The methylated adducts are converted to the corresponding vitamin D derivatives by extrusion of sulfur dioxide.

Studies on Biologically Active Pteridines. V. Synthesis of (6S)-5,6,7,8-Tetrahydro-1,3,5,6-tetramethyllumazine

Abstract (+)-5,6,7,8-Tetrahydro-1,3,5,6-tetramethyllumazine, a compound derived from enzymically reduced (−)-5,6,7,8-tetrahydro-6-methylpterin, was shown to be of (S)-configuration at the C-6 chiral center by a synthesis, which was performed by condensation of 5-bromo-6-chloro-1,3-dimethyluracil and (2S)-1-amino-2-(methylamino) propane. The structure of the condensation product was determined unequivocally by an independent synthesis using a regioselective methylation of 5,6,7,8-tetrahydro-1,3,6-trimethyllumazine.

ChemInform Abstract: METHYLATION OF TRICARBONYLCYCLOHEXADIENYLIRON SALTS WITH LITHIUM DIMETHYLCUPRATE

AbstractDie Titelreaktion der Salze (I) verläuft‐ stereospezifisch unter Bildung der Komplexe (II).

Methylation of tricarbonylcyclohexadienyliron salts with lithium dimethylcuprate

The reaction between various tricarbonylcyclohexadienyliron salts and lithium dimethylcuprate leads to stereospecific, regioselective methylation. Deuterium-labelled compounds are used to establish that alkylation occurs at the face of the dienyl system opposite to that occupied by Fe(CO)3.