An amino acid A, isolated from the acid-catalyzed hydrolysis of a peptide antibiotic, gave a positive test with ninhydrin and had a specific optical rotation (HCl solution) of 137.5° mL g^–1 dm^–1. Compound A was not identical to any of the amino acids in Table 27.1. The isoelectric point of compound A was found to be 9.4. Compound A could be prepared by the reaction of l- glutamine with Br₂ in NaOH, followed by neutralization. (See Sec. 23.11D.) Suggest a structure for A.

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TABLE 27.1 Names, Structures, Abbreviations, and Properties of the Twenty Common Naturally Occurring Amino Acids Name and abbreviations R* Amino acids with simple aliphatic side chains glycine, Gly, G alanine, Ala, A valine, Val, V leucine, Leu, L isoleucine, lle, I -H -CH3 -CH(CH3)₂ -CH₂CH(CH3)₂ -CH-CH₂CH3 CH3 [S configuration] General structure: Optical rotation of Lenantiomer in H₂O (sign of [a],) E EIE (+) (+) (-) (+) H₂N-CH- pka1 2.34 2.35 2.32 2.36 2.36 lo -0- pk₂z 9.60 9.69 9.62 9.60 9.68 РКаз Isoelectric point, pl 5.97 6.02 5.97 5.98 6.02