“…Ab acterial DTS from Allokutzneria albata with weak homology to SvS (34 %i dentical residues) converts GGPP into am ixture of the known fungal compound phomopsene (6) [33] and the new diterpene allokutznerene (7), together with traces of 5. [34] Thef ormation of 5 indicated af irst cyclisation step from GGPP to A5 + ,w hich is also ar easonable intermediate on the pathway to 6 and 7 (Scheme 5). Starting from A5 + ,aconcerted ring expansion/ring contraction and 2,10cyclisation to B6 + ,followed by a1,2-hydride shift to C6 + ,2,6cyclisation to D6 + ,and deprotonation yields 6.Avery similar sequence of steps including an alternative 6,10-cyclisation from A5 + to B7 + and subsequent 1,2-hydride shift to C7 + ,2,6cyclisation to D7 + ,a nd deprotonation gives rise to 7.T his mechanism was supported by labelling experiments with all twenty ( 13 C)GGPP isotopomers.T he substrates (3-13 C,2-2 H)GGPP and (7-13 C,6-2 H)GGPP,e nzymatically prepared from (3-13 C,2-2 H)FPP and IPP with GGPPS,e lucidated the 1,2-hydride shifts and deprotonation steps along the cationic cascade towards 6 and 7.N otably,t he DTS from A. albata is unrelated to the phomopsene synthase from Phomopsis amygdali, [33] thus suggesting convergent evolution leading to privileged diterpene structures.…”