Ortho-phthalaldehyde

The initial discoveries of the extension of the aromatic ring of the ortho-phthalaldehyde (OPA) to a naphthalene-2,3-dicarboxaldehyde (NBA) and the substitution of cyanide (CN ) for 2-ME as the nucleophile have provided the Center with a much more versatile reagent system (5,11), which maintains the sensitivity for primary aliphatic amines and amino acids, and now is known to form fluorescent products with oligopeptides, proteins, and other related analytes that possess a primary amine function (Equation 1). 

Walsh, S.E., Maillard, J.-Y. and Russell, A.D. (1999) Ortho-phthalaldehyde a possible alternative to glutaraldehyde for high level disinfection. ]. Appl. Microbiol., 86 (6), 1039-1046. 

OPA (ortho-phthalaldehyde) Aex = 340 nm, Aem = 455 nm. Derivatives are not stable (minutes). OPA is best used as a postcolumn derivatizing reagent. Precolumn use necessitates well-controlled and automated (mechanized) handling of the sample/reagents to ensure uniformity of time elapsed from reaction to injection. It reacts with primary amines only. Proline can be detected only if first converted to primary amine by oxidative reagents like chloramine T or sodium hypochlorite. Conversely, the concomitant reaction with OPA followed by FMOC obviates this problem and is the basis of the AminoQuant system marketed by Hewlett-Packard... 

A recent improvement builds on the fluorometric analysis of ammonium concentration (Holmes et al., 1999) with OPA (ortho-phthalaldehyde). Johnston et al. (2003) extracted the OPA-NH4+ derivative (1 -sulfonato-iso-indole) by soHd phase extraction and found that derivatized amino acids were not retained along with the indole on the column so that the method was specific. Since they developed the method for natural abundance work, the requisite high precision obhged analysis by CF-IRMS and its attendant high mass requirement (7.14 pmol N for a standard deviation of 0.5%o) that is difficult to achieve in oligotrophic waters. Since tracer experiments do not require such high precision, a lower mass could likely be used with the inherently lower precision GC—MS. 

OPA (ortho-phthalaldehyde) Fluorescent (ex. 340 nm, em. 455 nm) 50 fmol 90 min postcolumn, 17-35 precolumn Secondary amine pretreatment, slow reaction, unstable derivative, background interference Good reagent separation, high sensitivity and reproducibility with automated system... 

QACs and organomercurials. Phenols may or may not be mycobactericidal. Alkaline glutaralde-hyde exerts a lethal effect but more slowly than against other non-sporulating bacteria, but MAI is more resistant than M. tuberculosis. Recently, glu-taraldehyde-resistant M. chelonae strains have been isolated from endoscope washers. These strains remain sensitive to a new disinfectant used in endoscopy, the aromatic dialdehyde ortho-phthalaldehyde. 

Butcher, E.C. and Lowry, O.H., 1976. Measurement of nanogram quantities of protein by-hydrolysis followed by reaction with ortho-phthalaldehyde or determination of glutamate. Anal. Biochem., 76 502—523. 

After hydrolysis, the free amino acids are separated by ion exchange chromatography (section 2.3.2) or RP-HPLC (section 2.3.1). They can be identified according to their elution times and quantified according fo fheir elution volumes. To increase sensifivify, the amino acids are usually derivatised either pre- or post-column. Dansyl Chloride, Edman s reagent (Fig. 7.1) as well as ortho-phthalaldehyde (OPA) and 2-mercaptoethanol can be employed to form highly fluorescent adducts (Fig. 7.9) that can be detected easily. 

K. Gyimesi-Forras, A. Leitner, K. Akasaka and W. Lindner, Comparative study on the use of ortho-phthalaldehyde, naphthalene-2,3-dicarboal-dehyde and anthracene-2,3-dicarboaldehyde reagents for a-amino acids followed by the enantiomer separation of the formed isoindolin-l-one derivatives using quinine-type chiral stationary phases,/. Chromatogr., A, 2005, 1083, 80-88. 

A series of substituted ortho-phthalaldehydes has been prepared under mild conditions in respectable yields by oxidation of the corresponding dimethanols using oxalyl chloride activated DMSO [1343]. 

This same oxidation level situation - a disubstituted benzene with aldehyde (ketone) ortho to carbinol ready for cyclisation and dehydration to an isobenzofuran - can be achieved in alternative ways phthalaldehyde can be mono-acetalised, then the remaining aldehyde reduced, or lithiation technology can be utilised, as shown below. 

Three compounds also have two carboxyl groups the dicarboxylic acids. 1,2-Benzenedioc acid (phthalic acid, 35) has two carboxyl groups with an ortho relationship. In 1,3-benzenedioc acid (isophthalic acid), the carboxyl groups are meta, and in 1,4-benzenedioc acid (terephthalic acid) the carboxyl groups have a para relationship The dialdehyde compounds have related names 1,2-ben-zenedial (phthalaldehyde 36 also phthalic dicarboxaldehyde), 1,3-benzenedial (isophthalaldehyde also isophthalic dicarboxaldehyde), and 1,4-benzenedial (terephthalaldehyde also terephthalic dicarboxaldehyde). 

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