Natural products indirect synthetic methods

In this mini-review, selected and recent stereocon-trolled glycosylation methods, including direct and indirect glycosylations, as well as de novo synthetic approaches to 2-deoxyglycosides are introduced. In addition, recent applications of these methods to biologically active natural products possessing 2-deoxyglycosides are also described. 

Thyroid hormones also accelerate fetal lung maturation. Fetal thyroid hormone levels may be increased by antenatal administration of thyrotropin-releasing hormone (TRH), a tripeptide that crosses the placental barrier, stimulates fetal pituitary production of thyroid stimulating hormone (TSH), and which, in turn, increases fetal thyroid hormone production (Chapter 33). This indirect method of enhancement of fetal thyroid hormone production is utilized because thyroid hormones do not readily cross the placental barrier. Insulin delays surfactant synthesis and so fetal hyperinsulinemia in diabetic mothers may increase the incidence of RDS even in the full-term infant. Androgen synthesized in the fetal testis is the probable cause of a slower onset of surfactant production in male fetuses. Prophylactic, or after onset of RDS, administration of synthetic or natural pulmonary surfactants intratracheally to preterm infants improves oxygenation and decreases pulmonary morbidity. 

Size exclusion chromatography (SEC) is a method by which molecules can be separated according to their size in solution, thus relating indirectly to their molecular masses. To achieve this, stationary phases contain pores through which compounds are able to diffuse to a certain extent. Although the efficiency of separation can never attain that observed with HPLC, SEC has become an irreplaceable tool to separate natural macromolecules in order to study the distribution of synthetic polymer masses. Though the separation of compounds according to their sizes is not the most efficient process for small and medium molecules, this approach remains very useful in industry where the products are most often mixtures of compounds of very different masses. The instrumentation is comparable to that used in HPLC. 

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