Flavomannin Group

By far the most diverse group of dimeric pre-anthraquinones in regard to number and distribution are the flavomannin derivatives (Table 33). Interestingly, compounds of this type are not restricted to Cor-tinarius, subgenus Phlegmacium, but also occur in Dermocybe and in yellow Tricholoma species. Whereas Cortinarius and Dermocybe are closely related, the systematic relationship to Tricholoma is less obvious. 

The parent pigment of this group, flavomannin (343), the A type atropisomer of which has been isolated from Cortinarius odoratus, was first described as a metabolite of the mould Penicillium wortmanni (53). 

xanthochlorus 371), Dermocybe alnophila 401), D. as-penensis 403), D. cinnamomea, D. holoxantha 401), 

Racemic form Tricholoma auratum 291), [artefact] (629) Undetermined, TLC Cortinarius citrinolilacinus, C. subfulgens, C. sulfurinus, C. xanthophyllus 371), Dermocybe alnophila, D. cinnamomea, D. crocea, D. holoxantha, D. malicoria, D. schaefferi, D. sphagnogena, D. uliginosa 400) 

However, only very few toadstools produce pigments such as (343) in which both the 6- and 6 -hydroxy groups remain free. Notable among these is Cortinarius atrovirens which owes much of its dark green colour to the presence of 4,4 -dioxoflavomannin-A (346). 

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To obtain additional proof for the absolute configuration of the flavomannin group, we tried to carry out a synthesis starting with a diphenic acid derivative of known absolute configuration (Scheme 9). 

It can be summarised that the different methods of kinetic resolution and the synthetic correlations have led to the determination of stereochemistry at the biaryl linkage of atrivirin and flavomannin derivatives. Because the position and shape of the CD couplet around 275 nm is not much influenced by substituents present in the two halves of the dimers (refs. 3, 23), several other pigments can now be correlated. It will however need the development of further methods to elucidate the stereochemistry of the phlegmacin group and to determine the configuration of the chiral centers located in the alicyclic rings of the dimers. 

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