Carbohydrates, fluorinated, hydrogen

Some elements are essential to the composition or function of the body. Since the body is mostly water, hydrogen and oxygen are obviously essential elements. Carbon (C) is a component of all life molecules, including proteins, lipids, and carbohydrates. Nitrogen (N) is in all proteins. The other essential nonmetals are phosphorus (P), sulfur (S), chlorine (Cl), selenium (Se), fluorine (F), and iodine (I). The latter two are among the essential trace elements that are required in only small quantities, particularly as constituents of enzymes or as cofactors (nonprotein species essential for enzyme function). The metals present in macro amounts in the body are sodium (Na), potassium (K), and calcium (Ca). Essential trace elements are chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), molybdenum (Mo), nickel (Ni), and perhaps more elements that have not yet been established as essential. 

The biochemical rationale for incorporating fluorine in the carbohydrate residue is that replacement of a hydroxyl by fluorine would cause only a very minor steric perturbation of the structure or conformation while at the same time would have a profound electronic effect on neighboring groups. The substitution is possible while retaining the capacity of the position as an acceptor in hydrogen bonding. Yet these same attributes make the synthesis of fluorinated carbohydrates difficult. The synthesis of fluorinated carbohydrates offers a particularly fruitful field for the combination of modem chemical and enzymatic synthetic techniques. Total synthesis would be difficult because of the stereochemical control required at the multiple adjacent asymmetric centers of a fluorinated carbohydrate (105). 

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