Carboxylic hydrazides, labeled

Hydrazide-containing PEG-biotinylation reagents provide reactivity with carbonyl groups (e.g., aldehydes) to label carbohydrates or glycoproteins via hydrazone bond formation (Figures 18.19 and 18.20). The hydrazide group also may be coupled with carboxylate-containing... 

Kwakman et al. [65] described the synthesis of a new dansyl derivative for carboxylic acids. The label, N- (bromoacetyl)-A -[5-(dimethylamino)naphthalene-l-sulfonyl]-piperazine, reacted with both aliphatic and aromatic carboxylic acids in less than 30 min. Excess reagent was converted to a relatively polar compound and subsequently separated from the derivatives on a silica cartridge. A separation of carboxylic acid enantiomers was performed after labeling with either of three chiral labels and the applicability of the method was demonstrated by determinations of racemic ibuprofen in rat plasma and human urine [66], Other examples of labels used to derivatize carboxylic acids are 3-aminoperylene [67], various coumarin compounds [68], 9-anthracenemethanol [69], 6,7-dimethoxy-l-methyl-2(lH)-quinoxalinone-3-propionylcarboxylic acid hydrazide (quinoxalinone) [70], and a quinolizinocoumarin derivative termed Lumarin 4 [71],... 

Green 488 carboxylic acid, Cascade Blue hydrazide, FQ-labeled aspartic acid, CBQCA-labeled serine and tyrosine, GFP, TAMRA-labeled 20-mer oligonucleotide, and fluorescently labeled PS particles see Figure 5.20). This focusing effect leads to a pre-concentration factor of 10,000 or greater (from 8 nM to 90 dM for Oregon Green) [597]. 

The carboxyl group of the C-terminal amino acid is identified in a similar way, although the results are less reliable. One of the most common methods used involves converting all the C atoms into hydrazides. This liberates most, but not all, of the C-terminal residues in the sample and allows their identification. Further limitations occur as Asn and Gin cannot be liberated since their side chain amides are converted to hydrazides and Arg residues are converted to ornithine and are not liberated either. Another method uses acetic anhydride to form an oxalone specifically on the C-terminal residue. The converted residue can be labeled with deuterium or tritium and then liberated by hydrolysis and identified. 

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