Fmoc, 9-fluorenylmethoxycarbonyl removal

For the 9-fluorenylmethoxycarbonyl (Fmoc) protection of amino acids, Chinchilla et al.36,37 prepared a similar ROMP-polymer that supports an activated. V-hydroxysuccinimide Fmoc-carbonate (Table VII, entry 31). Various Fmoc-amino acids are prepared in pure form after removal of the polymer reagent by filtration and aqueous phase separation. 

Catalytic hydrogenation removed the Cbz protection from the nitrogen atom of isoxazolidine 333 without affecting the N-O bond. The nitrogen was then reprotected with 9-fluorenylmethoxycarbonyl chloroformate providing the A -Fmoc-protected isoxazolidine in 75% overall yield (Scheme 80) <2005BML1327>. 

A major progress in glycopeptide synthesis was achieved when it was demonstrated that the NHj-terminal 9-fluorenylmethoxycarbonyl (Fmoc) group can be selectively removed from glycopeptides using the weak base morpholine (pK 8.3). This holds true for 0-glycosyl serine and threonine esters, which are sensitive to base-catalyzed -elimination of the carbohydrate [10]. 

Table 10. Removal of fluorenylmethoxycarbonyl (Fmoc) group from relatively hydrophobic substrates and scavenging of the by-product dibenzofulvene (DBF) by different polymeric piperazine reagents...

In a variation of the Merrifield solid-phase peptide synthesis, the amino group is protected by a fluorenylmethoxycarbonyl (FMOC) group. This protecting group is removed by treatment with a weak base such as the secondary amine piperidine. Write a balanced equation and propose a mechanism for this deprotection. 

Amino groups are normally protected as their tm-butoxycarbonyl (Boc), carbobenzoxy-carbonyl (Z), or 9-fluorenylmethoxycarbonyl (Fmoc) derivative prepared as described in section 25.5. The Boc group may be removed by treatment with hy(kogen bromide. Other acidic reagents such as trifluoroacetic acid may also be used. 

Fluorenylmethoxycarbonyl (Fmoc) differs from benzyloxycarbonyl and Boc in that it is removable by treatment with bases such as ammonia. 

Fluorenylmethoxycarbonyl group) Deprotection (removal of Fmoc group)... 

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