Protective group of amine

Another protecting group of amines is 1-isopropylallyloxycarbonyl, which can be deprotected by decarboxylation and a /3-elimination reaction of the (tt-l-isopropylallyl)palladium intermediate under neutral conditions, generating CO2 and 4-methyl-1,3-pentadiene. The method can be applied to the amino acid 674 and peptides without racemization[437]. 

R)-Arbutamin was produced as follows 89.3 mg of (-)-l-di(t-butyldimethylsiloxy)phenyl)-2-aminoethanol, 50.0 mg of 4-(4-methoxymethoxyphenyl)butanoic acid, diethylphosphorylcyanide, and triethylamine were dissolved in N,N-dimethylformamide at 0°C, reacted at room temperature, so as to obtain 108.6 mg (in a yield of 82%) of amide compound. The amide compound obtained was reduced lithium aluminium hydride in an ether solvent at reflux temperature, so as to quantitative obtain amine. And 55.6 mg of (R)-arbutamin which is intended compound was obtained by deprotecting the hydroxyl-protecting group of amine in a methanol-THF solvent at room temperature using hydrochloric acid. 

The disadvantage of this method is that the dichloridites and monochloridites are sensitive to water and thus could not be used readily in automated oligonucleotide synthesis. This problem was overcome by Beaucage and Caruthers, who developed the phosphoramidite approach. In this method, derivatives of the form R 0P(NR2)2 react with one equivalent of an alcohol (catalyzed by species such as l//-tetrazole) to form diesters, R OP(OR")NR2, which usually are stable, easily handled solids. These phosphoroamidites are easily converted to phosphite triesters by reaction with a second alcohol (catalyzed by l//-tetrazole). Here, again, oxidation of the phosphite triester with aqueous iodine affords the phosphate triester. Over the years, numerous protective groups and amines have been examined for use in this approach. Much of the work has been reviewed. ... 

Ester group of l-(ethoxycarbonylmethyl)-7-aryl-5-oxo-1,2,3,5-tetrahydro-pyrido[l,2,3-i/e]quinoxaline-6-carboxamides was hydrolyzed and the 1-carboxymethyl moiety was converted to an aminocarbonylmethyl group with 1-methylpiperazine (01MIP12). Bromo atom of l-(2-bromoacetyl) derivatives was substituted by different amines. An amino group in the side chain attached to the position 1 of 7-aryl-5-oxo-l,2,3,5-tetrahydropyr-ido[l,2,3-i/e]quinoxaline-6-carboxamides was acylated, and terc-butoxycarbonyl protecting group of amino group was eliminated. 

The benzyloxycarbonyl protecting group for amines is introduced in high yield using benzyl imidazole-carboxylate with a catalytic amount (5%) of dimethylamino-pyridine.[1953... 

Scheme 8.5. Enzyme-triggered fragmentation of protective groups for amines, alcohols and carboxylic acids.

The electrochemical behavior of a series of nitrobenzenesulfonamides (48 and 49) were examined by cyclic voltammetry and other techniques in connection with the use of such arenesulfonyl groups as protecting groups for amines. Interestingly, the behavior of the 2-nitro derivative 48a and the iV.iV-dialkyl 4-nitro derivative 49 differed from that of the 3-nitro and 4-nitro monosulfonamides 48b and 48c62. Ortfco-derivative 48a and 49... 

An alternative approach is the cleavage of a UV-active protecting group from the resin, such as the widely used Fmoc Test. The quantitation of the 9-fluorenyl-methyloxycarbonyl (Fmoc) protecting group for amines is used in SPPS as an indirect method to determine the extent of a peptide coupling reaction. Similar approaches have also been recently reported for the quantitation of supported thiols [151, 154] and have also been the subject of an excellent review [148]. 

It is synthesized by the reaction of 3,4-dimethoxyphenyl-2-amine and l-(4-methoxyphenyl)-3-butanone with a simultaneous reduction of formed imine, giving the product (11.1.30), the methoxyl-protecting groups of which are cleaved by hydrogen bromide, giving dobutamine (11.1.31) [32,33]. 

Quite a wide range of substrates 100 could be converted into products 101 with high ee values since it is known that the N-protecting group of 101 can easily be cleaved, the approach represents a formal synthesis of optically active amines. It remains to be seen if this iridium/sulfoximine combination also opens up an alternative access to industrially relevant products such as the herbicide (S)-metolachlor produced by Syngenta [80]. 

Amines are important synthetic intermediates, and numerous protective groups have been developed for temporarily preventing amines from being acylated or alkylated. The following sections cover protective groups for amines that can be introduced or removed on insoluble supports. The development of such protective groups was mainly driven by solid-phase peptide synthesis. A more detailed collection of protective groups can be found in [230],... 

Most carbamates used as protective groups for amines are either acid-labile or base-labile. Deprotection proceeds by the mechanisms outlined in Figure 10.8. During the deprotection of acid-labile carbamates, carbocations are formed, which can alkylate electron-rich structural elements in a given substrate (e.g. phenols, thiols, indoles,... 

Enamines derived from simple ketones and aliphatic amines are too acid-labile and nucleophilic to be useful as protective group for amines. Triacylmethanes, however, form less basic enamines, which are sufficiently stable to be of use as amine protection. 

Several types of imine have been used as protective groups for amines in solution [230]. Most are stable towards bases, but can be hydrolyzed by acids. Benzophenone-derived imines can be prepared by treating support-bound aliphatic primary amines with benzophenone imine [148,260], but usually not by treatment with benzophenone. Polystyrene-bound benzophenone imines of glycine are sufficiently C,H-acidic to enable C-alkylation with alkyl halides [260,313] or Michael acceptors [314], and have mainly been used for this purpose (see Section 13.4.4). 

Yamashiro et al. 1972), boron trifluoride etherate in acetic acid (Schnabel et al. 1971), trimethylsylil triflate (Schmidt et al. 1987), trimethylsilyl perchlorate (Vorbrueggen Krolikiewicz 1975), and, most frequently, trifluoroacetic acid (Farowicki Kocienski 1995 and references therein). Deprotection of the /-HOC group under neutral conditions was not described until recently, yet it is highly desirable. Now it has been found that the tert-butoxycarbonyl protecting group for amines, alcohols, or thiols is removed efficiently (90-99% yield) with use of 0.2 equivalent of cerium ammonium nitrate in acetonitrile at 80°C (Hwu et al. 1996) ... 

The different reactivity of 1,2- and 1,1-acceptor/donor-substituted alkenes is paralleled by the readiness with which these compounds can be prepared. Thus, /3-amino acrylates are often spontaneously formed by mixing amines with /3-keto esters, and these derivatives have been used as protective groups for amines because of their low reactivity. a-Amino acrylates can, similarly, be prepared from a-keto esters [40], but this condensation reaction does not proceed spontaneously and requires chemical or azeotropic removal of water [41—43]. a-Amino acrylates are unstable compounds which must be stored at low temperatures [41] or N-acylated immediately after their generation [43]. 

The possibility of employing a wide range of nucleophilic radical sources, including alcohols, the choice of ideal protecting groups for amines, and the possibility of extending this process to ketimines by the development of a catalytic system in which TiCLt is associated with Zn, enables us to anticipate new frontiers for the synthesis of new structural types of a-amino acids and other amino-derivatives of crucial importance for chemistry, medicine, and life. 

The covalent C-B bonds of organoboronic acids and esters are very inert to ionic and radical reactions, thus allowing functionalization of remote sites other than the B-G bond (Equations (94)-(97)). Bulky diols such as pinacol have been used as the protecting group of B(OH)2 because of their high stability to nucleophiles and water and silica gel in amination of 316,474 hydroboration-amination of 317,475 Wittig reaction of 3 18,476 and oxidation-alkylation of 319.477... 

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