1-adamantyloxycarbonyl

Scheme 36 Reagents Used for the Introduction of the 1-Adamantyloxycarbonyl Group...

A further urethane protecting group derived from a secondary alcohol is the 2-ada-mantyloxycarbonyl group.It is more stable toward acidic reaction conditions than the corresponding 1-adamantyloxycarbonyl group (1-Adoc, Section 2.1.2.2.3.3.2), but it is removed with trifluoromethanesulfonic acid or anhydrous HF in a few minutes at... 

However, in the cases examined so far, the molar solubility in DMF has not increased significantly. The 1-adamantyloxycarbonyl (1-Adoc) group could potentially improve the solubility of amino acids and peptides protected by 1-Adoc in organic solvents due to its strong hydrophobicity.P Lys(l-Adoc) was successfully employed in the synthesis of peptide histidine isoleucine (PHI) (Scheme 9)P9 and in the synthesis of a peptide fragment of a lysozyme.P l... 

Peptide synthesis. The reagent has been used successfully for the N-protection of amino acids the bulky 1-adamantyloxycarbonyl group is removed by solvolysis with trifluoroacetic acid. The reagent was used also in the mixed-anhydride method of peptide synthesis, but considerable racemization was noted. 

Recent development of single-molecular force spectroscopy by atomic force microscopy (AFM) techniques has enabled quite successfully the measurement of mechanical force produced at a molecular level. Gaub and coworkers reported on a phototriggered polymer, which contains azobenzene units as part of the main polymer backbone (5 Adoc = 1-adamantyloxycarbonyl) (Holland et al., 2003 Hugel et al., 2002). This key study demonstrates a photomechanical cycle using... 

The 2-adamantyloxycarbonyl group has been found suitable for protection of the imidazole function in histidine during peptide synthesis.[7a]... 

The adamantyloxycarbonyl function has also been found to be a useful protecting group in peptide synthesis 209 The general reaction sequence is summarized in Scheme 19. The success of this peptide synthesis perhaps results from the bulk of the adamantyl group which directs attack to the desired carbonyl group. 

The reagents for the synthesis of Al -l-adamantyloxycarbonyl amino acid derivatives are similar to those used for other urethane-type protecting groups (Scheme 36). Although the related 1-adamantyl chloroformate (Adoc-Cl, 68) is obtained as crystalline solid, the acylation of amino acids under Schotten-Baumann conditions leads to significant decomposition of the reagent and thus its use does not result in satisfactory yields in all cases. Better results are obtained with 1-adamantyl fluoroformate (Adoc-F, 69) (yields of A -Adoc amino acids 85-95%)P I which is conunerciaUy available or readily prepared from adamantan-l-ol and... 

For a-amino protection, the urethane-type protecting groups derived from secondary alcohols do not offer improved properties compared to those of more classical groups derived from primary alcohols. The main advantage possibly derived from the use of this type of urethane-derived N -derivative is the increased solubihty, e.g. such as that reported for the 2-adamantyloxycarbonyl derivatives (see Section... 

With a similar intention, 1-adamantyl and 2-adamantyl residue-based protecting groups were developed. (3-1- and (3-2-Adamantylaspartates,P Y-(2-adamantyl)glutamate,P A -(2-ada-mantyloxycarbonyl)lysine,P l A -(2-adamantyloxycarbonyl)histidine,P Af -(l-adamantyl-... 

The m-Boc and S,m-bis-adamantyloxycarbonyl (Adoc) urethane derivatives of Arg have been used for Fmoc SPPS but appear to be inadequate for protection of the guanidino functionality and show substantial ornithine formation [176]. A ft>,a) -bis-Boc derivative has been reported to eliminate ornithine production, although lactam formation is not completely prevented [177]. 

Less acyl-transfer was noted with the benzyloxycarbonyl, the tert.butyl-oxycarbonyl and the adamantyloxycarbonyl groups. The acid stable piperi-dinocarbonyl group... 

Preparation of Bpoc-protected amino acids has been shown feasible in aqueous solvents using the corresponding fluorocarbonate illustrated in Chart 1. A series of even newer urethane type-protecting groups are presented in Chart 2. In histidine chemistry, protection of the N-imidazole position with the adamantyloxycarbonyl group has been shown to offer some advantages. A... 

Various aliphatic and alicyclic urethane-type derivatives have been used to protect the amino group (allyloxycarbonyl (40), cyclo-pentyloxycarbonyl (41) °, 1-methylcyclopentyloxycarbonyl (42), cyclohexyloxycarbonyl (43) (diisopropyl)methyloxycarbonyl (44)101. butyloxycarbonyl (46) ° ,f-amyloxycarbonyl 9-methyl-9-fluoronyloxycarbonyl (47) and adamantyloxycarbonyl... 

Fig. 6. Outline of the synthesis of glucagon by the solution procedure. DCCI, dicyclo-hexylcarbodiimide HOSU, N-hydroxysuccinimide NPS, 2-nitrophenylsulfenyl tBu, t-butyl AdOC, adamantyloxycarbonyl TFA, trifluoroacetic acid...

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