Quinoxalinols

Trimethyl-2,3-dihydro-2-quinoxalinamine 1,4-dioxide gave 2,2,3-trimethyl-1,2-dihydro-1-quinoxalinol 4-oxide (Pd/C, MeOH, H2 90% mechanism involed spontaneous loss of NHa). ... 

Both Form I (considered later) and Form II can be obtained by epitaxial crystallization. At atmospheric pressure, the unstable, chiral Form II can be forced to crystallize by using an appropriate substrate, namely 2-quinoxalinol, as assessed by the electron diffraction pattern (Fig. 5a) (no AFM images are available) [32], The contact plane is found to be (110)F... 

Fig. 5 (a) Diffraction pattern of sPP crystallized in its chiral Form II on p-quinoxalinol. The presence of reflections characteristic of this form and not observed for Form I confirms that the thin film as a whole is mostly in Form II. Chain axis vertical, (110) contact plane. Reproduced from [32] with permission (b) Illustration of the topographic interactions that induce Form II rather than Form I the hilly surface of the 2-quinoxalinol substrate (left, seen parallel to the contact face) can only accommodate the Form II (110) plane (middle, three chains shown, as seen parallel to the contact plane, chain axis vertical). The (110) plane of Form I (left, also three chains represented) has a profile that is not compatible with that of the substrate contact face... 

The quinoxalinol derivatives of a-ketovaleric acid and ketovaleric acid (internal standard) were separated on a LiChrospher 100 RP-8 column (4 mm x 250 mm). The mobile phase was a 60 40 ratio of 0.35 Af ammonium acetate and acetonitrile. The eluate was monitored by fluorescence with the excitation and emission wavelengths set at 340 and 420 nm, respectively. 

The quinoxalinol derivative obtained by reaction of pyruvate with o-phenylenediamine is chromatographed on a ChromSphere Q8 column (3 mm X 100 mm, 5 pim) at a flow rate of 0.4 mL/min using a mobile phase of 45% methanol, 1% acetic acid, and 54% water. The eluate was monitored by a fluorescence spectrometer using excitation and emission wavelengths of 336 and 420 nm, respectively. Calibration curves were constructed by adding known amounts of pyruvate to cytosolic fractions and carrying them through the derivatization and analysis procedures. 

Figure 13.2 a-keto acids were pre-column derivatized for 2h at 80 °C with o-phenylenediamine, producing fluorescent quinoxalinol compounds. 

Dihydroquinoxalines are obtained by the reaction of benzils with iV-phenyl-o-phenylenediamine thus reaction of the diamine with benzil gives 1,2-dihydro-l,2,3-triphenyl-2-quinoxalinol (6). The quinoxalinol is very readily transformed to the corresponding 2-alkoxyderivatives (7) on treatment with alcohols. 

The condensation product, before silylation, is a quinoxalinol. One advantage of this method over methoximation is that only one product is formed in methoximation syn- and a n -isomers of unsymmetrical oximes are observed ... 

The possible mechanism of the direct alkynylation of 2-quinoxalinone with p-tolylacetylene via Pd/Cu-catalyzed phosphonium coupling is proposed. It may involve the following seven-step cascade with two separate Pd/Cu catalytic cycles via C—H/C—OH bond activations (1) tautomer-ization of 2-quinoxalinone to 2-quinoxalinol in the presence ofEt3N (2) activation of 2-quinoxalinol with PyBroP generating the heterocycle— phosphonium intermediate (C-OH bond activation) (3) oxidative... 

The quinoxalinols may be analysed by TLC or HPLC, and are UV-absorbing and fluorescent [89]. For gas chromatogrphy silylation is necessary [86, 90]. Electron capturing derivatives have been made using p-chloro-, 4,5-dichloro- and 3,4,5,6-tetrafluoro-l,2-phenylenedia-mines [84]. 

Quinoxalinol formation with D-phenylenediamine a method for the determination of a-keto acids... 

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