Carbohydrate-based synthetic Subject

Nowadays, a strategic area of research is the development of polymers based on carbohydrates due to the worldwide focus on sustainable materials. Since the necessary multi-step synthesis of carbohydrate-based polymers is not economical for the production of commodity plastics, functionalization of synthetic polymers by carbohydrates has become a current subject of research. This aims to prepare new bioactive and biocompatible polymers capable of exerting a temporary therapeutic function. The large variety of methods of anchoring carbohydrates onto polymers as well as the current and potential applications of the functionalized polymers has been discussed recently in a critical review [171]. Of importance is that such modification renders not only functionality but also biodegradability to the synthetic polymers. 

Recently, the rapid preparation of carbohydrates has been facilitated by a synthetic route based on aldol coupling of three aldehydes used for the de novo production of polyol differentiated hexoses in only two chemical steps. The dimerization of alpha-oxyaldehydes, catalyzed by L-proline, is followed by a tandem Mukaiyama aldol addition-cyclization step catalyzed by a Lewis acid. Differentially protected glucose, allose, and mannose stereoisomers can each be selected, in high yield [46]. Microwave irradiation is becoming an increasingly popular method of carbohydrate synthesis and has been the subject of a recent review [47]. 

Some natural products outside the carbohydrate field - particularly those with highly hydroxylated cyclohexane ring components - have been subject to synthetic studies which are dependent on the mercury-based rearrangement reaction the alkaloid (+)-lycoricidine (30) [12] and the cycloheptane-based (+)-calystegine 62(31) which stimulates growth of nitrogen-fixing Rhizobia [29] are examples, and compound 32 which offers novel access to the anthracyclinone components of anthracyclin anti-cancer compounds, has been produced by cycloaddition of a naphthalene-based o-xylylene to a 2,3-unsaturated hex-4-uloside followed by carbocyclization of the product by use of the mercuration procedure [30]. Studies on HMG-CoA reductase inhibitors like compactin have afforded the tetra-carbon-substituted 33 made from a hex-5-enopyranoside with deoxy-branch chains at C-2, C-3 and C-4 [31]. 

The antitumour alkaloids of the pancratistatin and narciclasine classes have been the subject of several synthetic efforts this year. The L-mannonolactone derivative 51 is the starting material for a synthesis of narciclasine analogue 55 and two related compounds. The key transformations are elaboration of the carbohydrate adduct 53, derived by base-catalysed coupling of 51 with the anion derived from benzamide 52 to the cyclohexanone derivative 54. This involves selective removal of the C5,C6 isopropylidene group, oxidative cleavage of the C5,C6 bond and an intramolecular aldol reaction involving the C5-derived aldehyde and the benzylic ketone enolate (Scheme 10). ... 

---