R-Butyloxycarbonyl group

The monoaminomonophosphonic acids, either in the free state or, very often, as their diethyl esters, have been resolved by the usual techniques of repeated crystallization of appropriate salts those of L-(+)-tartaric acid (2,3-dihydroxybutanedioic acid) or its mono-or di-benzoyl derivativesor of D-(-)-mandelic acid, have been widely employed the use of di-O-benzoylated L-tartaric anhydride, which is based on the separation of diastereoisomeric amides (111), has also been employed to a limited extent. In selected cases, such as the monoaminomonophosphonocarboxylic acids or A -acylated (aminoalkyl)phosphonic acids, resolution following salt formation with organic bases has also been carried out ephedrine, quinine and both enantiomers of l-phenylethylamine have all been used. In many cases, only one enantiomer of the (aminoalkyl)phosphonic acid (or diester) has been isolated in optically pure form. Sometimes, the acidity of the substrate, and hence choice of base for resolution, can be modified by using a mono- (as opposed to di-) ester or (or even in addition to) protection of the amino group as, for example, the phthalimido, benzyloxycarbonyl (cbz) or r r -butyloxycarbonyl (boc) derivative. Resolved di- and mono-esters can be hydrolysed to the free acids under acidic conditions, and A -protection can also be removed through the customary procedures. 

Chiral intermediates for the synthesis of (-)-anisomycin (1) and (+)-anisomycin (anti-1) (153), (R)-2-(p-methoxyphenyl)methyl-2,5-dihydro-pyrrole (142) and its (S)-isomer (+)-187, have been efficiently synthesized from D-tyrosine and L-tyrosine, respectively (Scheme 20) [28]. D-tyrosine was converted to 0-methyl D-tyrosine methyl ester (182) [72-75] which was treated with di-tert-butyl dicarbonate to protect the amino group. Subsequent reduction of the ester group with sodium borohydride in the presence of lithium chloride furnished the alcohol 183. Swern oxidation of 183 followed by chain extension with the anion derived from bis(2,2,2-trifluoroethyl)(ethoxycarbonylmethyl)-phosphonate afforded (Z)-Q ,/0-unsaturated ester (184), which was used immediately without purification to avoid or minimize any possible racemization of the chiral center. Reduction of the ester group of 184 with diisobutylaluminium hydride afforded the alcohol 185 which after mesylation followed by intramolecular cyclization gave the desired 2,5-dihydropyrrole derivative 186. Removal of the tert-butyloxycarbonyl group was achieved by treatment with trifuoroacetic acid to give (-)-142 in 62% overall yield from 182. The (S)-2,5-dihydropyrrole (-l-)-187 was also prepared in the same manner starting from L-tyrosine. Since (-l-)-187 had been transformed into (-l-)-anisomycin (anti-1) (153), (-)-142 could also be transformed to the (-)-anisomycin (1) [26,66]. 

The r -alkoxycarbonyl residues, e. g., the tert-butyloxycarbonyl groups, are cleaved under acid-catalyzed conditions ... 

AMINO GROUP Boron trifluoride ether-ale. l-r-Bulyloxycarbonyltriazole-1,2,4, Di-t-butyl dicarbonate. 4-Dimethylamino-1-t-butyloxycarbonyl pyridinium chloride. CARBONYL GROUP Ceric ammonium nitrate. 1,2-Dihydroxy-3-bromopropane. Sodium N-chloro-p-toluenesulfonamide. Thallium(lll) nitrate. Trichloroethanol. Trimcthylsilyl cyanide. Chloromethyl methyl sulfide. N,N -Diisopropylhydra-zinc. Trichloroethanol. 

Mention might also be included here of the nature and potential importance of the choice of amino-protection and ester groupings in work on the aminophosphonic acids. The choice of groups for protection at nitrogen is obviously based on experience in conventional amino acid chemistry, and both r rr-butyloxycarbonyl (boc) and benzyloxy-carbonyl (cbz) groups are extensively employed. Most recorded syntheses of aminoalkyl-phosphonic and -phosphinic acids have relied on diethyl or dimethyl esters, largely as a consequence of the ready availability of the simple trialkyl phosphites and dialkyl hydro-genphosphonates the same esters are also preparable under mild conditions from the free acids by the action of ortho esters RC(OR )3 (R = H or Me, R = Me or Until... 

Alakhov, Yu. B., A. A. Kiryushkin, V. M. Lipkin, and G. W. A. Milne Butyl-ation of the Tryptophan Indole Ring a Side-Reaction during the Removal of -Butyloxycarbonyl and r-Butyl Protecting Group in Peptide Synthesis. J. C. S. Chem. Commun. 406-407 (1970). 

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