Tert-Butoxycarbonyl group

This approach may find application in peptide bond formation that would eliminate the use of irritating and corrosive chemicals such as trifluoroacetic acid and piperidine as has been demonstrated recently for the deprotection of N-boc groups (Scheme 6.7) a solvent-free deprotection of N-tert-butoxycarbonyl group occurs upon exposure to microwave irradiation in the presence of neutral alumina doped with aluminum chloride (Scheme 6.7) [41]. 

Reaction of the anion of tert-butyl isocyanoacetate with oxiranes gives the y-hydroxy products 11, which upon mesylation can be transformed by an intramolecular alkylation to the iso-cyanocyclopropanecarboxylates 12, the precursors of 1-amino-cyclopropanecarboxylates100. The cyclization 11 — 12 shows a relatively high degree of stereoselectivity due to the difference in bulkiness betwen the isocyano and the tert-butoxycarbonyl groups. 

The benzyloxycarbonyl group, but not the tert-butoxycarbonyl group, may be removed by catalytic hydrogenation. Again a carbamic acid is formed, which readily loses C02 ... 

Keywords (V-tert-butoxycarbonyl group, aluminium chloride, microwave irradiation, amine... 

A versatile ring opening of five- and six-membered cyclic carbamates yielding acyclic, V-protected 1,2- and 1,3-amino alcohols involves protection with the AT-tert-butoxycarbonyl group, followed by cleavage with cesium carbonate in methanol13. 

Initial attempts to extend this procedure to the synthesis of peptides gave the products in good yields, at least at the level of model dipeptides when DMAP was added in catalytic amounts.This may be attributed to the intermediate formation of the highly reactive 1-(tert-butoxycarbonyl)-4-(dimethylamino)pyridinium tert-butyl carbonate (10, Scheme 7) which facilitates the nucleophilic addition of the amino acid carboxylate anion at the tert-butoxycarbonyl group of the pyridinium system. Such an intermediate has been confirmed by Knolker and Braxmeier.t The addition of DMAP was not found to induce racemization. Whether this procedure is applicable in repetitive steps of peptide synthesis, is still questionable since tert-butoxycarbonylation of the amino component, at least to some extents, cannot be excluded. 

Finally, acylation of the amine 9g with acetyl chloride in the presence of N,N-diisopropylethylamine affords compound 9b. The saponification and acidic removal of the tert-butoxycarbonyl groups of 9h complete the synthesis of 9 as a trifluoroacetic acid salt. 

The optimization strategy will be exemplified by a rather difficult isomer separation. The product to be separated was a relatively strong base and first experiments using neat solvents on different types of stationary phases (silica gel, amino-, cyano-, and diol-modffied silica gel) revealed that it would be very difficult to separate the two isomers on a larger scale. Therefore, synthetic chemists were contacted to modify one of the secondary base functions with an easily removable BOC (tert-butoxycarbonyl) group. 

The acid-catalyzed cleavage of the tert-butoxycarbonyl group Is the best method to form the parent benzazepinone. Other methods used have been the Pd/C hydrogenolysis of a benzyloxycarbonyl group,and zinc mediated reductive cleavage of trichloroethoxy and trichloro-tert-butoxy carbonyl groups. ... 

Keywords A-tert-butoxycarbonyl group, Yb(OTf)3, silica gel, amide... 

The procedure described here offers a general route to 7-substltuted indolines.3 The method is based on the directed ortho-lithiation of N-(tert-butoxycarbonyl)aniline derivatives.4 The tert-butoxycarbonyl group seems to be essential for C-7 selective lithiation, since other directing groups so far reported promote C-2 metalation on the indoline ring.5 The C-7 selective lithiation of 1-(tert-butoxycarbonyl)indoline is in contrast to the C-2 selective lithiation of 1-(tert-butoxycarbonyl)indole.6... 

Faced with the shortcomings of the polyphthaldehyde resist (presented helow in chemical amplification resists based on depolymerization), the search for chemically amplified DUV resists resulted in a quick switch to more stable materials based on poly(p-hydroxystyrene), a phenolic polymer that Willson et al. were studying as a potential replacement for novolac. They observed that poly(p-tert-butoxycarbonyloxystyrene) (PBOCST), which is poly(vinyl phenol) protected with tert-butoxycarbonyl groups (t-BOC), is far more stable than the unprotected p-hydroxystyrene and could be purified and polymerized under controlled conditions. The resulting protected polymer could be easily deprotected thermally by heating it to 200°C or to a much lower temperature (100°C) by treatment with acid generated from the exposure of onium salts, just as in the poly(phthaldehyde)... 

Scheme 8.10. Deprotection of N-tert-butoxycarbonyl group on alumina.

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