New homo-sesquiterpenes are accessible after conversion of presilphiperfolan-8β-ol synthase (BcBOT2) with cyclopropylmethyl analogs of farnesyl diphosphate, and this biotransformation is dependent on subtle structural refinements. Two of the three cyclisation products are homo variants of germacrene D and germacrene D-4-ol while the third product reported contains a new bicyclic backbone for which no analogue in nature has been described so far. The findings on diphosphate activation are discussed and rationalised by relaxed force constants and dissociation energies computed at the DFT level of theory.