Removal of Protective Groups

Total Synthesis of Palytoxin Carboxylic Ad An Example of the Selection, Introduction, and Removal of Protective Groups... 

Me3SiI, CH3CN, 25-50°, 100% yield. Selective removal of protective groups is possible with this reagent since a carbamate, =NCOOCMe3, is cleaved in 6 min at 25° an aryl benzyl ether is cleaved in 100% yield, with no formation of 3-benzyltyrosine, in 1 h at 50°, at which time a methyl ester begins to be cleaved. 

C. Factors Governing Selectivity in Removal of Protecting Groups... 

Tnflic acid is a useful reagent for the removal of protecting groups (deblocking) in synthetic proteins [67] At the same time, it is an excellent catalyst for the protection of a variety of phenols in the form of their terf-butyl ethers [5(5] (equation 37)... 

SYNTHESIS OF COMPLEX SUBSTANCES TWO EXAMPLES (AS USED IN THE SYNTHESIS OF HIMASTATIN AND PALYTOXIN) OF THE SELECTION, INTRODUCTION, AND REMOVAL OF PROTECTIVE GROUPS... 

For a review covering the photolytic removal of protective groups, see V. N. R. Pillai, Synthesis, 1 (1980). 

SOME GENERAL METHODS FOR PHOSPHATE ESTER FORMATION REMOVAL OF PROTECTIVE GROUPS FROM PHOSPHORUS... 

All the approaches for deblocking protective groups described earlier in this book have found application in the removal of protective groups from phosphorus derivatives. Because phosphate protection and deprotection are commonly associated with compounds that contain acid-sensitive sites (e.g., glycosidic linkages and DMTr-O- groups of nucleotides), the most widely used protective groups on phosphorus are those that are deblocked by base. 

Indicate conditions that would be appropriate for the following transformations involving introduction or removal of protective groups ... 

The transformations shown below have been carried out using reaction sequences involving several oxidation steps. Devise a series of steps that could accomplish these transformations and suggest reagents that would be suitable for each step. Some sequences may also require nonoxidative steps, such as introduction or removal of protecting groups. 

Dipolar addition of ethyl propiolate to the nitrile oxide 285, prepared by chlorination of the corresponding oxime, gave, after removal of protecting groups, the C-glycosyl-isoxazole205 (286). These reactions further demonstrate the utility of anomerically functionalized C-/3-D-ribofuranosyl derivatives that can be prepared from the versatile aldehyde 100. 

Benzyl and triphenylmethyl ethers of carbohydrates are preferred over methyl ethers when selective removal of protecting groups is important. The relatively high nucleophilic activity of the 5-hydroxyl group in glycosides and 1,2-O-alkylidene derivatives of 4 permits its benzylation and triphenylmethylation under mild conditions. Thus, treatment of 33 (Ref. 34) and 36 (Ref. 57) with benzyl bromide and... 

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