Synthetic Studies of Panellus Luciferin

The structures of PMs are trimeric, consisting of three molecules of PS and two molecules of methylamine that are condensed together (Table 9.5). In the structures of PMs, however, the bonds created by the condensation lack adjacent hydrogen atoms, making the connectivity assignment in 1H-NMR studies virtually impossible (see the 9-membered rings in Fig. 9.11). To circumvent this problem, a model compound of panal, K-l, having 13C-labeles at the C12 and C13 positions, has been synthesized at Kishi s laboratory (Harvard University) to make a model compound of PM (Stojanovic, 1995). 

In the activation of PS-A and PS-B, treatment with methylamine resulted in a considerably higher chemiluminescence activity than with other amines. In the case of K-1, however, a significantly higher chemiluminescence activity was obtained with (NH SC or with hexy-lamine than with methylamine. In spite of this finding, methylamine was used in the activation of K-1 to prepare a model compound of PM. 

l3C-labeled K-1 (2 mg) was treated with 4 mM methylamine in a mixture of methanol (6 ml) and 0.2 M sodium acetate buffer pH 3.6 (1.5 ml) at 50°C for 2 hr, and the product was purified by HPLC on a column of PRP-1 (50-85% acetonitrile gradient, in the presence of 0.1 M acetic acid and lOmM NaCl). Two weakly chemiluminescent compounds, KM-1 (5% yield) and KM-2 (1% yield), were obtained. 

Both compounds were non-fluorescent. Compound KM-1 was similar to PMs in the absorption maximum (A.max 488 nm) but not in the spectral shape, whereas KM-2 was similar to PMs in the spectral shape but not in the absorption maximum at 515 nm (Fig. 9.10). The chemical structures of KM-1 and KM-2 have been determined by high-resolution mass spectrometry and NMR spectrometry (Fig. 9.11 Stojanovic, 1995). 

The compound KM-1 is composed of three molecules each of K-l and methylamine in its structural formula, differing from PM that is made from three molecules of PS and two molecules of methylamine. However, KM-2 is composed of three molecules of K-l and two molecules of methylamine, corresponding to the formula of PM. 

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