Protecting Groups in Synthesis

FIGURE 16.44 A protecting group can be used to mask a sensitive functional group while reactions are carried out on other parts of the molecule. When these reactions are completed, the original functionality can be regenerated. 

An acetai (stabie in base) the carbonyi group is protected, or masked 

Another type of protecting group for alcohols is a silyl ether. A silyl ether has the general formula of R —O—SiR3. The reaction of an alcohol with a trialkylsilyl halide leads to a trialkylsilyl ether in near-quantitative yield 

alcohols can be protected by converting them into THP or silyl ethers, and regenerating them when needed. 

11 Addition Reactions of Nitrogen Bases Imine and Enamine Formation 

---

These oxazolines have cationic surface-active properties and are emulsifying agents of the water-in-oil type. They ate acid acceptors and, in some cases, corrosion inhibitors (see Corrosion). Reaction to oxazoline also is useful as a tool for determination of double-bond location in fatty acids (2), or for use as a protective group in synthesis (3). The oxazolines from AEPD and TRIS AMINO contain hydroxyl groups that can be esterified easily, giving waxes (qv) with saturated acids and drying oils (qv) with unsaturated acids. 

Fluonnated organosihcon compounds are very useful for introduction of tnalkylsilyl protecting groups in synthesis TVialkylsilyl trifluoroacetamides are perhaps the best known of these agents, for they can be used to prepare stlyl ethers orsdyl esters [91, 92] (equation 76)... 

Sjolin, P, Kihlherg, J, Use of fluorobenzoyl protective groups in synthesis of glycopeptides (1-ehmination of O-hnked carbohydrates is suppressed, J. Org. Chem., 66, 2957-2965, 2001. 

Phenylurethane (carbamate) derivatives of insoluble polysaccharides, produced by reaction with PhNCO in neutral organic solvents, are used in determination of molecular weight distributions (see Section 4.5.1) carbamates are acid stable and base labile and have better alternatives as protecting groups in synthesis. 

Compound Q contains a cyclic acetal acetals are commonly used as protecting groups in synthesis (Section 8.3.5.2)... 

Solved Exercise 17-8 Working with the Concepts Using an Acetal Protecting Group in Synthesis... 

Jones, R A., Fritz, H J., and Khorana, H G. (1978) Studies on polynucleotides 147 Use of the lipophilic rerr-butyldiphenylsilyl protecting group in synthesis and rapid separation of polynucleotides. Biochemistry 17, 1268-1278 Mishra, R. K. and Misra, K. (1988) Protecting groups as purification tool in large-scale synthesis of small oligodeoxynucleotides Indian J, Chem Sect. B, 27B, 817-820. 

Another concept used to determine the efficiency of synthesis is step economy [3]. Synthesizing a complex molecule typically involves multiple steps, and the concept of step economy minimizes the number of steps needed for the synthesis. The use of protecting groups adds two steps, protection and deprotection, and thus lowers the step economy. This generates interest in minimizing the use of protecting groups in synthesis. 

---