Carbohydrates are involved in a wide range of biological processes. These structurally diverse compounds are more complex than other biological polymers, and are often present as heterogeneous mixtures in nature. The chemical synthesis of carbohydrates is one way to obtain pure oligosaccharides, but it is hampered by difficulties associated with the regioselective protection of polyhydroxyls and challenges related to the stereoselective assembly of glycosidic linkages. Here we describe a combinatorial, and highly-regioselective, method that can be used to protect individual hydroxy groups of a monosaccharide. This approach can be used to install an orthogonal protecting group pattern in a single reaction vessel (a 'one-pot' reaction), which removes the need to carry out the time-consuming isolation and purification of intermediates. Hundreds of building blocks have been efficiently prepared starting from d-glucose, and the iterative coupling of these building blocks enabled us to assemble beta-1,6-glucans and a library of oligosaccharides based on the influenza-virus-binding trisaccharide.

Carbohydrates, which are ubiquitously distributed throughout the three domains of life, play significant roles in a variety of vital biological processes. Access to unique and homogeneous carbohydrate materials is important to understand their physical properties, biological functions, and disease-related features. It is difficult to isolate carbohydrates in acceptable purity and amounts from natural sources. Therefore, complex saccharides with well-defined structures are often most conviently accessed through chemical syntheses. Two major hurdles, regioselective protection and stereoselective glycosylation, are faced by carbohydrate chemists in synthesizing these highly complicated molecules. Over the past few years, there has been a radical change in tackling these problems and speeding up the synthesis of oligosaccharides. This is largely due to the development of one-pot protection, one-pot glycosylation, and one-pot protection-glycosylation protocols and streamlined approaches to orthogonally protected building blocks, including those from rare sugars, that can be used in glycan coupling. In addition, new automated strategies for oligosaccharide syntheses have been reported not only for program-controlled assembly on solid support but also by the stepwise glycosylation in solution phase. As a result, various sugar molecules with highly complex, large structures could be successfully synthesized. To summarize these recent advances, this review describes the methodologies for one-pot protection and their one-pot glycosylation into the complex glycans and the chronological developments associated with automated syntheses of oligosaccharides.

There is evidence indicating that ingestion of arsenic may predispose the development of diabetes mellitus in arsenic-endemic areas in Taiwan. However, the prevalence of diabetes and related vascular diseases in the entire southwestern arseniasis-endemic and nonendemic areas remains to be elucidated. We used the National Health Insurance Database for 1999-2000 to derive the prevalence of non-insulin-dependent diabetes and related vascular diseases by age and sex among residents in southwestern arseniasis-endemic and nonendemic areas in Taiwan. The study included 66,667 residents living in endemic areas and 639,667 in nonendemic areas, all ≥ 25 years of age. The status of diabetes and vascular diseases was ascertained through disease diagnosis and treatment prescription included in the reimbursement claims of clinics and hospitals. The prevalence of non-insulin-dependent diabetes, age-and gender-adjusted to the general population in Taiwan, was 7.5% (95% confidence interval, 7.4-7.7%) in the arseniasis-endemic areas and 3.5% (3.5-3.6%) in the nonendemic areas. Among both diabetics and nondiabetics, higher prevalence of microvascular and macrovascular diseases was observed in arseniasis-endemic than in the nonendemic areas. Age-and gender-adjusted prevalence of microvascular disease in endemic and nonendemic areas was 20.0% and 6.0%, respectively, for diabetics, and 8.6% and 1.0%, respectively, for nondiabetics. The corresponding prevalence of macrovascular disease was 25.3% and 13.7% for diabetics, and 12.3% and 5.5% for nondiabetics. Arsenic has been suggested to increase the risk of non-insulin-dependent diabetes mellitus and its related micro-and macrovascular diseases.

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