The Synthesis of Rare Sugars

The use of new oxidation reagents, such as the Pfitzner-Moffatt reagent, dimethyl sulfoxide-acid anhydrides, and ruthenium tetroxide, has significantly improved the yields obtained on oxidation of a secondary hydroxyl group to a carbonyl group in suitably protected sugars. The application of these new oxidants in the carbohydrate field is briefly surveyed. The product ketones are convenient intermediates for syntheses of amino, branched-chain, deoxy, and other rare sugars. Some representative syntheses are illustrated.     

An Alternative Approach for the Synthesis of Sulfoquinovosyldiacylglycerol

Sulfoquinovosyldiacylglycerol (SQDG) is a glycolipid ubiquitously found in photosynthetically active organisms. It has attracted much attention in recent years due to its biological activities. Similarly, the increasing demand for vegan and functional foods has led to a growing interest in micronutrients such as sulfolipids and their physiological influence on human health. To study this influence, reference materials are needed for developing new analytical methods and providing enough material for model studies on the biological activity. However, the availability of these materials is limited by the difficulty to isolate and purify sulfolipids from natural sources and the unavailability of chemical standards on the market. Consequently, an alternative synthetic route for the comprehensive preparation of sulfolipids was established. Here, the synthesis of a sulfolipid with two identical saturated fatty acids is described exemplarily. The method opens possibilities for the preparation of a diverse range of interesting derivatives with different saturated and unsaturated fatty acids.     

An Alternative Approach to the Synthesis of Parvistone C

A stereoselective total synthesis of parvistone C, an oxygenated natural styryllactone, has been accomplished in excellent overall yield by employing asymmetric aldol reaction, asymmetric epoxidation and regioselective epoxide ring opening as the key steps. Our synthetic strategy is very simple, concise and no use of protecting groups.     

Sago Pith Residue as an Alternative Cheap Substrate for Fermentable Sugars Production

Sago pith residue is one of the most abundant lignocellulosic biomass which can serve as an alternative cheap substrate for fermentable sugars production. This residue is the fibrous waste left behind after the starch extraction process and contains significant amounts of starch (58%), cellulose (23%), hemicellulose (9.2%) and lignin (3.9%). The conversion of sago pith residue into fermentable sugars is commonly performed using cellulolytic enzymes or known as cellulases. In this study, crude cellulases were produced by two local isolates, Trichoderma asperellum UPM1 and Aspergillus fumigatus, UPM2 using sago pith residue as substrate. A. fumigatus UPM2 gave the highest FPase, CMCase and ??-glucosidase activities of 0.39, 23.99 and 0.78 U/ml, respectively, on day 5. The highest activity of FPase, CMCase and ??-glucosidase by T. asperellum UPM1 was 0.27, 12.03 and 0.42 U/ml, respectively, on day 7. The crude enzyme obtained from A. fumigatus UPM2 using ??-glucosidase as the rate-limiting enzyme (3.9, 11.7 and 23.4?IU) was used for the saccharification process to convert 5% (w/v) sago pith residue into reducing sugars. Hydrolysis of sago pith residue using crude enzyme containing ??-glucosidase with 23.4?IU, produced by A. fumigatus UPM2 gave higher reducing sugars production of 20.77?g/l with overall hydrolysis percentage of 73%.     

Oxazolidines From Sugars. III. A New Method for N-Alkyl and N,N-Dialkyl-D-Glucosamine Derivatives

Abstract

Title compounds can be synthesised by an easy two-step method from the readily available benzyl 2-acylamino-4,6-O-benzylidene-2-deoxy-D-glucopyranosides (1–5), by nucleophilic cleavage of the oxazolidine ring previously formed between the positions 2 and 3 of the aminosugars.     

An Alternative Synthesis of Quindoline and one of its Closely Related Derivatives

The alkaloid Quindoline (13) and one of its tetracyclic isomer indazolo[2,3-a]quinoline (8) have been synthesised utilising the Pd(0)-catalysed cross-coupling reaction of pivaloylamino phenylboronic acid (2) with substituted quinolines.     

A Practical Approach to the Synthesis of Dianhydro Sugars

Chiral tetrols derived from various carbohydrate precursors have been converted into the corresponding dianhydro sugar derivatives in a one pot procedure. The course of reaction very much depends upon the protecting groups used. In case of D-mannitol and sorbitol, it has been shown that when 3,4-hydroxy groups are protected as trans-acetonide group, the present methodology furnished exclusively 1,2: 5,6-dianhydro derivatives in excellent yield. However, if the 3,4-hydroxy groups are protected with benzyl group a mixture of products consisting of dianhydro sugar, a furan and a bicyclo[2.2.2]octane derivatives were obtained. This method has also been used to synthesize dianhydro sugars in which the two diol moieties are placed adjacent to each other or separated by one or more carbon atoms.     

Reactive Distillation: An Attractive Alternative for the Synthesis of Unsaturated Polyester

Summary: Unsaturated polyester is traditionally produced in a batch wise operating reaction vessel connected to a distillation unit. An attractive alternative for the synthesis of unsaturated polyester is a reactive distillation. To value such alternative synthesis route reliable process models need to be developed. In this paper, the strategy is described for the development of the reactive distillation model. Essential parts of the reactive distillation model are kinetic and thermodynamic which are subsequently validated with the experimental data of the traditional batch process such as acid value of the polyester, weight of the distillate and glycol concentration in the distillate. We find that the models predict these important variables reliably. Unsaturated polyester production time is around 12 hours in the traditional batch process. However, the simulation study of the reactive distillation process shows that the total production time of unsaturated polyester in a continuous reactive distillation system is between 1.5 hours to 2 hours for the same product quality as during batch production. The equilibrium conversion is raised by 7% compared to the traditional batch process. The model demonstrated that reactive distillation has the potential to intensify the process by factor of 6 to 8 in comparison to the batch reactor.     

An Alternative Approach to the Synthesis of Poly(naphthoylenebenzimidazole)s

An alternative approach to the synthesis of poly(naphthoylenebenzimidazole)s in supercritical carbon dioxide has been accomplished without use of hazardous chemical solvents, which resulted in preparation of high-purity polymers by a more efficient contemporary method. A series of poly(naphthoylenebenzimidazole) s has been obtained at 90°C and 15 MPa for 8 h with the use of a mixture of benzoic acid and benzimidazole as a catalyst. Certain properties of the synthesized polymers have been studied.     

An improved synthesis of 3,6-diamino-1,2,4,5-tetrazine. II. From triaminoguanidine and 2,4-pentanedione

A new synthesis for the title compound that gives an 80% overall yield was developed. Treatment of triaminoguanidine monohydrochloride ( 1 ) with 2,4-pentanedione ( 2 ) gave 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine ( 3 ) in 80–85% yield. Oxidation of 3 with nitric oxide or nitrogen dioxide to 3,6-bis(3,5-dimethyylpyrazol-1-yl)-1,2,4,5-tetrazine ( 4 ) followed by ammonolysis of 4 gave 3,6-diamino-1,2,4,5-tetrazine ( 5 ) in guantitatively yields.     

An Effective Synthesis of α-Azido Ketones From Ketones

One-pot transformation of ketones into α-azido ketones has been achieved by successive treatment with HNIB and NaN₃ in acetonitrile.     

Synthesis of hydrothioxanthenes. II

Ethylenedicyclohexanone and phosphorus pentasulfide give 9-methyloctahydrothioxanthene (II) (yield ～37%), a small amount of 9-methylperhydrothioxanthene (IV) (～2%), and 9-methylthioxanthene (VI) (～1%). Reaction with hydrogen sulfide gives a high yield of thioxanthene II (64–65%). The behavior of II in dehydrogenation over Pd/C, and of II and IV to oxidation are investigated. IR spectrum data are given for II and its sulfone.     

An Alternative Stereoselective Synthesis of Protected Trans-5-Alkyl-4-Hydroxy-2-Pyrrolidinones

A flexible approach to protected trans-5-alkyl-4-hydroxy-2-pyrrolidinones was described. The key step involved the α-amidoalkylation of benzene-sulfone derived from (S)-malic acid, with organozinc reagents generated in situ from Grignard reagents and anhydrous ZnCl₂-OEt₂.     

Synthesis of Blocked Sugars Bearing a Terminal 1-Cyanovinyl Group

Abstract

A series of blocked sugar aldehydes treated with the conjugate base of nitromethane afforded the expected nitrosugars 1–7, whose configuration at the new asymmetric centre was assigned by CD. Nitroenoses 8–14, obtained from the corresponding saturated β-hydroxy nitrosugars, reacted with potassium cyanide, afforded the terminal 1-cyanovinyl sugar derivatives 15–23. Another route to 1-cyanovinylic sugars bearing a free hydroxy group (24 and 25) consisted in reacting aldehydo sugars with the conjugate base of acrylonitrile. The 1-cyanovinyl sugars are soft electrophiles which react with hydroxylamines to give the product of a conjugate addition (27 and 28). The interest of these compounds resides in their often selective toxicity towards cells, viruses or bacteria.