Structure of the 2,4-dinitrophenylhydrazine adduct of pyrroloquinolinequinone (PQQ) dimethyl ethyl triester, C24H18N6O11

The chemistry of heterocyclic o-quinone cofactors

“…The benzoquinolinequinone (35) was synthesized by a Doebner-von Miller-type annulation between 3-amino-2-naphthol and dimethyl 2-oxoglutaconate and a subsequent oxidation with Fremy's salt [(KSO,),NO] (Scheme 5). 29 The synthesis of (41) was achieved by constructing 2-carbomethoxybenz[indole (38) from 1 -aminonaphthalene by a JappKlingemann reaction with methyl 2-methylacetoacetate and a subsequent Fischer indolization reaction. The quinone function was introduced by a Fremy's salt oxidation of 5-aminoindole (40), which was prepared from (38)…”

“…29 The synthesis of (41) was achieved by constructing 2-carbomethoxybenz[indole (38) from 1 -aminonaphthalene by a JappKlingemann reaction with methyl 2-methylacetoacetate and a subsequent Fischer indolization reaction. The quinone function was introduced by a Fremy's salt oxidation of 5-aminoindole (40), which was prepared from (38)…”

“…The addition position of C-5 was confirmed by X-ray crystallographic analysis of the ethyl ester derivative of ( 5 l). 38 When aminoguanidine was used, intramolecular cyclization and then aromatization of the corresponding hydrazone took place to give the triazine derivative (54). 37 It is interesting to note that the redox reaction (reduction of…”

Crystal structure of a calcium(II)–pyrroloquinoline quinone (PQQ) complex outside a protein environment

“…After the structure of MDH was elucidated in 1978-79 (Duine et al, 1978;Westerling et al, 1979;Salisbury et al, 1979), the cofactor attracted much attention in the following years, with articles published concerning its total synthesis (Corey & Tramontano, 1981), redox chemistry (Eckert et al, 1982), metal coordination (Noar et al, 1985) and small-molecule interaction (van Koningsveld et al, 1985). Itoh and coworkers published several articles presenting the interaction of PQQ with Ca and other alkaline earth metals (Itoh et al, 1997(Itoh et al, , 1998, and the synthesis of model compounds, mimicking the active site of MDH (Itoh et al, 2000).…”