This is an important and challenging task, especially in case of the coupling reaction of bromaminic acid (4) with 2,5-diaminobenzenesulfonic acid (5) to yield 8, which represents a key step in the synthesis of MG 50-3-1 (3) [21] with typically low yield (10%) [21]

This is an important and challenging task, especially in case of the coupling reaction of bromaminic acid (4) with 2,5-diaminobenzenesulfonic acid (5) to yield 8, which represents a key step in the synthesis of MG 50-3-1 (3) [21] with typically low yield (10%) [21]. on retrosynthetic analysis. A new, regioselective Ullmann coupling reaction under microwave irradiation was successfully developed to obtain 1-amino-4-(4-amino-2-sulfophenylamino)-9,10-dioxo-9,10-dihydro-anthracene 2-sulfonate (8). Four different copper catalysts (Cu, CuCl, CuCl2, and CuSO4) were investigated at different pH values of sodium phosphate buffer, and in water in the absence or presence of base. Results showed that CuSO4 in water in the presence of triethylamine provided the best conditions for the regioselective Ullmann coupling reaction yielding the key intermediate compound 8. A new synthon (sodium 2-(4,6-dichloro-1,3,5-triazin-2-ylamino)benzenesulfonate, 13) which can easily be obtained on a gram scale was prepared, and 13 was successfully coupled with 8 yielding the target compound 3. as well as evaluation of the drug, and Benzyl isothiocyanate thus may provide information valuable for the development of antagonists for P2Y1 and P2Y1-like receptors. Furthermore, the compound will be a useful biological tool for investigating purinergic signalling, for example in the intestine. 2. Results and Discussion Previous studies showed that the substitution pattern in the 4Cposition of the anthraquinone moiety plays a crucial role for the ability of the compounds to antagonize P2Y receptor subtypes, such as P2X1 and P2Y1-like [21], P2X2 [22], P2Y2 [23], and P2Y12 receptors [24,25] and to inhibit nucleoside triphosphate diphosphohydrolase Benzyl isothiocyanate (NTPDase) isoenzymes [26] and ecto-5-nucleotidase [27]. Recently we developed a microwave-assisted Ullmann coupling reaction of bromaminic acid with a diverse range of aniline derivatives in the presence of elemental copper (Cu0) in sodium phosphate buffer [28,29]. In the present study we examined the impact of the buffer pH, and the use of different copper catalysts at different pH values on the described microwave-assisted Ullmann coupling reaction. We were especially interested in the question of how regioselectivity could be achieved in the presence of two nonequivalent amino groups on the aromatic system. This is an important and challenging task, especially in case of the coupling reaction of bromaminic acid (4) with 2,5-diaminobenzenesulfonic acid (5) to yield 8, which represents a key step in the synthesis of MG 50-3-1 (3) [21] with typically low yield (10%) [21]. For direct comparison of the developed reaction we examined the coupling of bromaminic acid (4) with the isomeric 2,4-diaminobenzenesulfonic acid (6). 2.1. Optimization of the Ullmann Benzyl isothiocyanate Coupling Reaction of Bromaminic Acid with Aniline In order to systematically optimize the microwave-catalyzed Ullmann coupling reaction [28] of bromaminic acid with anilines, we initially investigated the effects of the sodium buffer pH in the presence of four different copper catalysts having three different oxidation states (0, I and II) in a model reaction, namely the coupling reaction of bromaminic acid sodium salt (4) with aniline yielding Acid Blue 25 (AB-25, 7) as outlined in Table 1. It should be noted that the pH values were measured at the start of the reaction at 23 C (see Table 1, Table 2 and Table 4) as the reaction mixtures turned acidic during the course of the reactions due to the formation of hydrogen bromide. Table 1 Impact of different pH values on the synthesis of AB-25 in the presence of a copper catalyst. ratio Conversion and the sulfonate ratio was estimated by RP-TLC using a mixture of acetone/water (1:4) as eluent; this is possible because all components (starting material and product) have different colors: the starting material is red, while the product is blue and the by-product is dark-red or violet. Yield was estimated based on RP-TLC results. Table 4 Effects of different pH values on the coupling reaction of bromaminic acid (4) with 2,4-diaminobenzene sulfonic acid (6). ratio Conversion and the sulfonate ratio was estimated by Mouse monoclonal to BNP RP-TLC using a mixture of acetone/water (1:4) as eluent, this is possible because all components (starting material and product) have different colors: the starting material is red, while the product is blue and the by-product is dark-red or violet. Yield was estimated based on the RP-TLC results. Elemental copper (Cu) and copper(I) chloride (CuCl) gave almost the same results: they differed only in two cases, when water (pH 7, entry 1) was used as a solvent, or in acidic buffer (NaH2PO4, pH 4.8, entry 2), Cu being superior in both cases. The reaction occurred in the presence of Cu within 20C25 min with ca. 50% conversion. In the case of CuCl no conversion at all was observed in water or acidic media (pH 7 and 4.8, entry 1 and 2, respectively, Table 1), even.