NEW N-GLUCOSYLATED SUBSTITUTED ANILINES

Abstract. The reaction of (+)-D-glucose 1 with 4-chloroaniline 6b or 3,5-dibromoaniline 12 leads almost exclusively to the β-configuration of N-glucosylated anilines 7b and 13. Acetylated derivatives 8b, 14 and 15 were obtained by dissolving/suspending substance s 7b and 13 in Ac2O/Py mixture. The acetylation of 2-(3,5dibromophenylamino)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol 13 is less selective than in the case of the 2-(4-chlorophenylamino)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol 7b and leads to compounds 2(acetoxymethyl)-6-(3,5-dibromophenylamino)tetrahydro-2H-pyran-3,4,5-triyl triacetate 14 and 2-(acetoxymethyl)6-(3,5-dibromophenylamino)-5-hydroxytetrahydro-2H-pyran-3,4-diyl diacetate 15 in a 2:1 ratio. The product 14 is formed with greater selectivity and in a higher yield (up to 80%) when the reaction is catalyzed by DMAP and stored for one week at +4C.


Introduction
N-Glycosylated anilines represent an important product scaffold cluster by virtue of their bioactivity and as intermediates for generating further molecular complexity including natural compounds [1], for example some natural alkaloids.The vital roles played by sugars in biological systems continue to be unravelled.It is known that, various drugs, amino acids, sugars and many other chiral natural compounds show different infl uence on human organism, their biological properties being directly dependent on chirality.That is why the "structure-property" relationship should be studied very well.From the other side, properties are determined by the structure.It means, construction of chemically pure and defi ned molecule is an interesting and important goal in synthetic chemistry.
Langer et al. [1,2] has shortly offered the opinion that the preparation of analogues of N-glycosylated indolinones in high yields remains an important problem of carbohydrate and medicinal chemistry.This challenge also applies to the related problem of synthesis of N-linked alkaloids.For example, Kamano, Y. et al. [3], reported the isolation of the alkaloids -Convolutamydines A, B, and C from bryozoan Amathia convoluta, see Figure 1.In contrast to the pharmacologically inactive non-glycosylated indigo, N-glycosylated indigo demonstrate a considerable growth inhibitory activity toward various human tumor cell lines [4,5].
Our approaches to N-glucosylated indoline-2,3-dione 4 from (+)-D-glucose 1 and N-glucosylated 3-hydroxy-2-oxindole 5 are presented below.They show benefi t from the rapid advances in mainstream carbohydrate chemistry, allowing for convenient integration in glucosylated Convolutamydine A-E and analogues of structure 5 preparation (see Figure 1).Chemistry Journal of Moldova.General, Industrial and Ecological Chemistry.2015, 10( 2), 62-67 The main purpose of the present research was to test the effectiveness of this approach for the synthesis of halogen phenylamino-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triyl triacetates from the corresponding intermediates 3 (see Figure 1).It has already been demonstrated that such type compounds are suitable building units for the synthesis of a variety of non-halogenated isatin-N-glucosides [1,2].We also report in this paper the preparation of 3,5-dibromoaniline 12.
In fact compound 7b shows in the 1 H NMR spectrum a clear triplet at δ Н 4.30-4.34ppm with the magnitude of a spin-spin coupling constant J=8 Hz and an important peak at 883.8 cm -1 in its IR-spectrum, which is characteristic for a β-anomer.
The acetylation reaction of 13 was performed with acetic anhydride in pyridine and lead to esters 14.The reaction was very slow (one week) and after work-up two main products in the obtained mixture were then separated by column chromatography over silica gel.
Additionally, another product was isolated, which presumably corresponded to the structure 15.According to NMR data, the isolated product is a mixture of compounds 14 and 15 in 2:1 ratio, which has been determined by integration of the signals belonging to the acetate groups.It could be easily identifi ed according to 13 C NMR spectrum by the double set of signals: four C=O groups at δ C 169.6, 169.9, 170.7 and 171.3 ppm for compound 14, and three C=O groups for compound 15 at δ C 169.1, 169.5 and 170.4 respectively.Similarly, double set of signals has been noted for pyranic (δ C 60-83 ppm) and aromatic (δ C 115-147 ppm) parts of molecules of the discussed derivative (see experimental part).Thus, the 1 H NMR spectrum shows multiplets at δ Н 3.85-3.90,4.01-4.30,4.99-5.07,5.16-5.20 and 5.30-5.46ppm, which are characteristic for pyranic part (CH and OH), two doublets at δ Н 6.74 and 7.00 ppm and two triplets centered at δ Н 7.10 and 7.14 ppm (aromatic), four singlets at δ Н 2.04, 2.05, 2.06 and 2.07 ppm for compound 14, a singlet at δ Н 2.03 ppm and a doublet centered at δ Н 2.08 ppm for compound 15, respectively.
Catalysis by pyridine is of the nucleophilic type and it is known that 4-(N,N-dimethylamino)pyridine is a better catalyst when pyridine fails.Indeed, compound 13 readily undergoes reaction with acetic anhydride under analogues conditions in presence 4-(N,N-dimethylamino)pyridine to yield up to 90% compound 14.

Conclusions
The present work demonstrates that interaction of 4-chloro-and 3,5-dibromo-substituted anilines with (+)-D-glucose affords N-glycosylated adducts 7b and 13 as β-anomers.The position and steric course of further estherifi cation are catalytically dependent.We confi rmed that in the case of 4-chloro substituted aniline reaction with Ac 2 O in Py occurs mainly to give tetra-acetate 8b.On the contrary, reaction of 3,5-dibromo substituted aniline gives a mixture of adducts 14 and 15 in a 2:1 ratio with overall yield 65%.In the case when the reaction was catalysed by 4-(N,N-dimethylamino)pyridine only compound 14 was obtained in 80% overall yield.The structures of all new compounds 13, 14 and 15, including confi gurations of anomeric carbon atoms, were characterized through IR and NMR spectroscopic methods.

Experimental
All used solvents were of reagent quality, and all commercial reagents were used without additional purifi cation.Removal of all solvents was carried out under reduced pressure.Analytical TLC plates Silufol ® UV-254 (Silpearl on aluminum foil, Czecho-Slovakia) were used and spots were detected under UV-lamp with wavelength 254 nm.
M. p.s (uncorrected) were determined on a Boetius apparatus.IR spectra were recorded on a Spectrum 100 FT-IR spectrophotometer (Perkin -Elmer) using the universal ATR sampling accessory. 1H and 13 C NMR spectra were registered in CDCl 3 and DMSO-d 6 2-% solution on a "Bruker-Avance III" (400.13 and 100.61MHz) spectrometer.

General procedure for the synthesis of N-glucosylated anilines 7b and 13.
To a solution of (+)-D-glucose 1 (2g, 0.011 mol) in 25 mL of absolute methanol corresponding aniline (6b or 12) (0.013 mol) was added.The mixture was refl uxed for 24 hours.After completion of the reaction (TLC control, solvent system 2% MeOH in CH 2 Cl 2 ) the mixture was stored in refrigerator at sub-zero temperature so long, as white volume is being precipitated.The precipitate was fi ltered and washed with methanol and dried at room temperature.

Procedure for the synthesis of compound 8b.
The anilide 7b is maximally dissolved in dry pyridine under stirring (for every hydroxyl group 1.8-2.0eq. of pyridine are used) and cooled in an ice bath to 0 0 C.Then, freshly distillated acetic anhydride is rapidly added (for every hydroxyl group 1.5-1.6 eq. of acetic anhydride are used).Stirring is continued at the same temperature until a homogeneous solution appeared (about 3 hours).The mixture was hold for 24-48 hours in a refrigerator without stirring.After completion of the V. Pogrebnoi / Chem.J. Mold. 2015, 10(2), 62-67 reaction (TLC control, system hexane-ethyl acetate 4:1), the mixture was poured into ice-water (1:2) and extracted with ethyl acetate (4x30 mL).The combined organic phases were washed with sodium hydrogen carbonate solution, water and brine, dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure.The resulting white solid mass was recrystallised from methanol.The bittern was evaporated and recrystallised again.The obtained product is white solid.
General procedure for the synthesis of compounds 14 and 15.Method A: The anilide 13 is maximally dissolved in dry pyridine under stirring (for every hydroxyl group 1.8-2.0eq. of pyridine are used) and cooled in an ice bath to 0 0 C.Then, freshly distillated acetic anhydride is rapidly added (for every hydroxyl group 1.5-1.6 eq. of acetic anhydride are used).Stirring is continued at the same temperature until a homogeneous solution appeared (about 3 hours).The mixture was hold for 24-48 hours in a refrigerator without stirring.After completion of the reaction (TLC control, system hexane-ethyl acetate 4:1), the mixture was poured into ice-water (1:2) and extracted with ethyl acetate (4x30 mL).The combined organic phases were washed with sodium hydrogen carbonate solution, water and brine, dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure.The resulting oily mass was purifi ed by column chromatography on silica gel, using as eluent hexane-ethyl acetate (6:1 to 3:1).