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Diversity-Oriented Synthesis of Substituted and Fused β-Carbolines from 1-Formyl-9H-β-Carboline Scaffolds
Published in Tanmoy Chakraborty, Lalita Ledwani, Research Methodology in Chemical Sciences, 2017
Nisha Devi, Ravindra K. Rawal, Virender Singh
Takasu et al.20 reported the synthesis of several β-carboline-based compounds, including the natural products, Kumujancine, 4-methoxy vinyl β-carboline (MVC), creatine, and their corresponding salts. The synthetic strategy involved the Pictet–Spengler reaction of tryptamine with ethyl glyoxalate in ethanol, followed by acylation with acetyl chloride to furnish THβC 24 in 44% yields. Treatment of THβC 24 with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) led to an unstable 4-oxocarboline derivative (25), which upon reaction with dimethoxypropane in the presence of para toluenesulfonic acid (p-TSA) under azeotropic conditions, followed by oxidative aromatization, produced 1-ethoxycarbonyl-4-methoxy-β-carboline (26) along with demethoxy compound (X= H; Kumujian A). Subsequent reduction of ester 26 with diisobutylaluminum hydride (DIBAL-H) produced the aldehyde 5 and Kumujancine (27). Finally, Wittig olefination of 27 afforded the first total synthesis of MVC (28). The β-carbolinium cations (29) were also prepared from the corresponding β-carbolines by simple quaternerization with either alkyl tosylates or alkylhalides (Scheme 5.6). These products were evaluated for in vitro antimalarial activity against Plasmodium faciparum and also for cytotoxicity studies. It was observed that quaternary carbolinium salts showed much higher potencies than the corresponding neutral β-carbolines. MVC exhibited EC50 5 × 10−6 M against P. faciparum in in vitro assay.
New Uses for Hemicellulose
Published in Jorge M.T.B. Varejão, Biomass, Bioproducts and Biofuels, 2022
Monosaccharides, such as xylose or arabinose, are aldehydes—organic compounds known for their strong reducing properties and reactivity. Adding groups to the carbonyl group of the aldehyde is a well-known branch of organic chemistry. If ethanol production is the goal from C5 sugars, a new possibility may emerge, combining chemistry with biochemistry, and may have the strength to potentially constitute a means of converting C5 sugars into ethanol. Several chemical reactions make possible to add a group,CH2, to the pentoses, converting them to hexoses, if necessary with another hydroxyl group –CH2OH. A problem arises in this addition of carbon—sugars and Nature exercise strict control over stereocenters in their building blocks— and chemistry often has difficulty making reactions in a stereo-specific manner. The insertion of one more carbon should ideally be done so that the final sugar—a hexose—results in the D configuration, that is only one of the two possible stereo geometries. In general, known reactions result in the formation of a racemic mixture. However, in the literature, there are cases in which microorganisms were able to convert stereoisomers of sugar-related substances into ethanol (Kamzolova et al. 2018) by expression of enzymes capable of rearranging their structures (Pikis et al. 2006). An example of this possibility occurs with arabinose, as shown in Figure 3, where the oxidative addition of a –CH2- group results in a mixture of D-Glucose plus D-Mannose. Since these sugars are interconvertible via fructose through the transformation of Lobry from Bruyn-van Ekenstein (Stahlberg et al. 2012), the fermentation of both to ethanol is possible. The addition of carbon can be done by different chemical reactions. The addition of sodium cyanide to aldose arabinose followed by reduction with hydrogen or aqueous acid in the presence of a suitable catalyst, produces a mixture of D-Glucose plus D-Mannose, via the Kiliani-Fischer reaction (Nishimura et al. 1994). The same products can be obtained using diisobutylaluminum hydride (DIBAL-H) route 2 at the top, Figure 3 (Ban et al. 2017). The use of bromodichloromethane may be another possibility by addition of the Grignard type to the carbonyl group and producing a formylation product by hydrolysis (Stepowska et al. 1999). A third possibility is shown in Figure 2 with the addition of carbon monoxide followed by reduction by catalytic hydrogenation (Chatani et al. 1995).
Strategies for introducing sulfur atom in a sugar ring: synthesis of 5-thioaldopyranoses and their NMR data
Published in Journal of Sulfur Chemistry, 2019
By 2002, Stasiket et al. [120], investigated the usefulness of 1,4-lactone templates [121], as building blocks to prepare various 5-thiopentoses analogues [119]. Two approaches were investigated (Scheme 35). In route A, selective bromination of the primary hydroxyl group in d-ribono-1,4-lactone 204 by thionyl bromide in DMF gave the corresponding 5-bromo lactone 205. Acetonation of the diol with I2 in the presence of dry acetone produced 206 in 80% yield. Compound 206 underwent reduction with diisobutylaluminium hydride (DIBAL-H) followed by nucleophilic substitution of the bromide group in 207 by using thioacetate in the presence of DMF solvent afforded the key 5-S-acetyl-2,3-O-isopropylidene-5-thio-d-ribofuranose 208 in quantitative yield. Methanolysis of 208 with NaOMe in methanol gave 2,3-O-isopropylidene-5-thio-d-ribopyranose 209. Acid hydrolysis of the resulting free thiol 209 furnished 5-thio-d-ribopyranose 193 in 90% yield. In an alternative mode, the reaction of 5-bromo-5-deoxy-2,3-O-isopropylidene-d-ribofuranose 207 with potassium thioacyanate gave 210 in 98% yield. Treatment of 210 with activated zinc in acetic acid afforded the desired free 5-thio-d-ribopyranose 193. In route B, the bromo lactone 205 was acetylated to give the bromo diacetal 211. Displacement of the bromide group with potassium thioacetate gave the 5-thioacetate-d-ribono-1,4-lactone. The thioacetate group was subjected to reduction with disiamylborane in THF and followed by removal of the acetyl groups with NaOMe in methanol furnished the globally deprotected 5-thio-d-ribopyranose 193. The overall yield of the reaction sequence of route A was 46%. On the other hand, the overall yield of the reaction sequence of route B was 57%.