Protection of amino group

Metal hydrides reduce preferably polar double bonds, whereas catalytic hydrogenation is somewhat selective for non-polar double bonds. Selective protection of amino groups in amino acids. 

TtM use of vinyl chloroformate tor N-dealkytatlon of tertiary amines, protection of amino groups, protection of hydroxyl groups or formation of Z-ketoimidazoles. Synthesis of vtnyl cartxjnates by means of fluoro or chiorofonnates. 

An important example is the preparation of carbobenzoxy chloride (PhCH20C0Cl) from phosgene and benzyl alcohol. This compound is widely used for protection of amino groups during peptide synthesis (see 10-55). 

PROTECTION OF AMINO GROUPS ACYLATION AND DIMER FORMATION... 

FIGURE 3.14 Protection of amino groups as urethanes by reaction with chloroformates (path... 

FIGURE 3.15 Protection of amino groups as urethanes by reaction with succinimido carbonates (path A).33-36 The mixed carbonate is a weaker electrophile than the chloroformate. The V-alkoxycarbonylamino-acid anion does not react with the reagent (path B) in the presence of the weak base hence no dimer is formed. R = triethyl or dicyclohexyl. 

FIGURE 3.17 Reagents for protection of amino groups as the ferf-butoxycarbonyl derivatives. terf-Butyl chloroformate is rarely used because of its low boiling point. The oxime is 2-ferf-butoxycarbonyloximino-2-phenylacetonitrile,45 Boc20 = di-ferf-butyl dicarbonate, or di-terf-butyl pyrocarbonate.46 (Tarbell et al., 1972 Pozdvev, 1974). Acylations are carried out at pH 9 to avoid dimerization. 

The protection of amino groups of amino sugars benefits particularly from the use of new blocking groups introduced for peptide synthesis. In this context, light-sensitive urethans and amides that can be utilized for the protection of amino groups in amino sugars are of particular interest in saccharide synthesis and modification. 

Scheme 5. Reaction conditions i, reductive amination ii, protection of amino group iii, Collins reagent iv, Ph3F CHCioH2i" v, hydrolysis vi, Hg(OAc>2 vii, NaBH4 viii, l-decen-3-one ix, ethanedithiol x, Raney Ni xi, HCl-EtOH.

SB protection of amino groups has been removed by a catalytic amount of NaOMe in MeOH at 50°C <86SC809>, KOH in MeOH at reflux <88TL6537> and BSB protection has been removed by inorganic alkalies in MeOH at RT <91T9807>, but as a rule deprotection by acid hydrolysis proceeds more readily (cf. Section 4.24.1.3.3). 

Reagent used for the protection of amino groups. Because of the steric influence of the Boc protecting group, it is quite stable to base hydrolysis and catalytic reduction with hydrogen. 

DNS derivatives of amino acids and peptides are used for the protection of amino groups, separation by TLC and fluorimetric analysis. DNS derivatives can be also used for MS identification and have been employed for the confirmation of a large number of biogenic amines [209]. The molecular ions of these derivatives are usually intense and are often accompanied by an ion at m/e 170 or 171 as the key fragment. BNS derivatives are also useful for MS identification of amines of biological interest [82,83]. 

Full details are available for preparation of this reagent, which is useful for protection of amino groups and which is not commercially available.1... 

Protection of amino groups. The o-nitrobenzenesulfenyl (NPS) group is useful for protection of terminal amino groups of peptides and the exocyclic amino groups of bases such as adenine. The group also increases the stability of an N-glycoside bond. It is removable by reduction with Bu3P in aqueous dioxane.12 It is also stable to phosphorylation. These properties have been used to synthesize... 

It was clear that the protection of amino group and the presence of an a-COOH group in homoserine complicated samarium-based C-glycosylation. 

Protection of amino groups. The reagent (I) reacts with amino acid esters to give N-r-butoxycarbonyl (/-BOC) derivatives (2) in good yield. In a typical procedure glycine ethyl ester hydrochloride is suspended in chloroform and NaHCOj in water... 

Cp3)2C6H3B(OH)2 is useful for the regioselective protection of amino groups (Sch. 4) [169]. For example, verbacine has been synthesized by adding cinnamoyl chloride to a 1 1 mixture of 16-phenyl-2,6,ll,15-tetraazacycloheptadecan-l-one and... 

The use of ethoxycarbonyl-protected amino acids as well as methoxycarbonyl derivatives for peptide synthesis was reported in 1903 by Fischer, although the protecting groups in related peptide derivatives could not be cleaved without affecting the peptide bonds,f since urethanes derived from aliphatic primary alcohols are about as stable as the amide bond. Thus, this type of carbamate can only be used for reversible protection of amino groups, at least in... 

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