phellinicola (Röhrich et al. 2013a), which is considered comparatively rare. The additional substituent of the C-terminal Tyrol of voglmayrins 12−17 (compounds 46−51), which has tentatively been assigned as a prenyl or isoprenyl (C5H8) residue, is hypothesised to be located at the p-hydroxy group. A regiospecific O-prenylation at the 4-position of the aromatic ring has recently been demonstrated for SirD (Zou et al. 2011), a tyrosine

O-prenyltranferase (Kremer and Li 2010) catalysing the first pathway-specific step in the biosynthesis of the phytotoxin sirodesmin PL. The latter is produced by Leptosphaeria maculans (anamorph: Phoma lingam), the causal agent of blackleg of canola (Brassica napus). Recently, O-prenyltyrosine diketopiperazines have been described from Fusarium sp. and Penicillium crustosum (Guimarães et al. find more 2010). Another notable structural element, dihydroxy-Pheol was found at the C-terminus of hypocitrin-1 (compound 69). While the presence of either Pheol or Tyrol may be assumed to originate from the relaxed substrate specificity in the terminal adenylate domain of the respective peptaibol

synthetase, the direct incorporation of dihydroxy-Phe, presumably 3,4-dihydroxy-L-Phe (DOPA), is one possible biosynthetic route. Fungal tyrosinases are known to oxidise not only Tyr and various other monophenols, e.g. in the route to melanins, but also act on tyrosyl residues within peptides and proteins, leading to the formation of inter- and intra-molecular crosslinks (Selinheimo et al. 2007). Thus, Tyrol-containing peptaibols could be further RXDX-101 oxidised by tyrosinases, and even become attached to components of the fungal cell wall (Mattinen et al. 2008). Considering the sequences of all species screened, including those of H. pulvinata and H. phellinicola, a general building scheme for those SF1-peptaibiotics can be given (Table 13): Table 13 General building scheme of the sequences of Hypocrea/Trichoderma SF1-peptaibiotics

RG7420 concentration screened (Röhrich et al. 2012, 2013a, this study)   Residue 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19a 20b Ac Aib Ala Aib Ala Aib Ala Gln Aib Lxx Aib Gly Lxx Aib Pro Vxx Aib Vxx Gln Gln Pheol   (Vxx) (Ser) Ala Aib (Vxx) (Aib)   (Vxx) Aib (Ala) Ala (Vxx) (Vxx)   Lxx Tau-protein kinase (Vxx) Aib (Glu) – Lxxol     (Aib) (Ser) (Lxx) (Phe)     (Ala) (Vxx)   (Ser) (Aib)     (Aib)   (Lxx)   (Glu) (Vxxol)     (Lxx) (Vxx) (Ser) (Ala)                             (Tyrol)     (Vxx)   (Gly) (Lxx)                             (Tyr(C5H8)ol)                                         (di-OH-Pheol) Minor sequence variants are parenthesised aOne of the Gln/Glu residues is deleted in some of the truncated sequences bThe C-terminal amino alcohol is deleted in some of the truncated sequences As can be seen from above, all structural features (Röhrich et al. 2012) required for ion channel formation (Grigoriev et al.