homogosodesmine. GCMS comparison of the synthetically derived material with the crude extract confirmed the structure of 5 as both the mass spectrum and GC retention time matched (Fig. -S14; Table ). Additionally, catalytic hydrogenation of a sample of synthetic 5 provided a mixture of isomers of 8 whose mass spectra and GC retention times were identical to those obtained from the hydrogenation of the millipede extracts. Compounds 4 and 6 are close structural analogs of 3 and 5, respectively, but based on the hydrogenation experiment they have only one olefin. Both alkaloids showed a loss of 85 Da in their mass spectra, which is typical of a loss of C6H13. This loss was observed in the mass spectra of 7 and 8 and represented the loss of the saturated side chain from the heterocyclic core, so initially we hypothesized that the olefin was within the ring systems. Fortuitously, treatment of a portion of the crude extract with dilute HCl (aq) and subsequent neutralization resulted in the addition of water (Fig. ). The mass spectra of the hydrate adduct showed a loss of methyl (15 Da), intense ions for the loss of C3H7O fragment (59 Da) as well as the corresponding fragment at 59 m/z that would be expected from a dimethyl tertiary alcohol (Fig. ). Thus, indicating that the olefin in 4 and 6 is on the sidechain opposed to within the bicyclic system. Since B. petasata produces all four analogs, they are likely the product of the same biosynthetic pathway with the olefins installed at the same position. Therefore, we hypothesized that the sole olefin in 4 and 6 was most likely between C11 and C12. The observed loss of 85 Da in 3 and 5 is hypothesized to result from a radical rearrangement that shifts the olefin to the bicyclic system (Fig. ). To confirm these hypotheses, total syntheses were attempted to produce both the hydrate adducts of 4 and 6 from 8-indolizidone and 2-quinolizidone, respectively (Scheme 2). First, 12 and 13 were reacted with triethylphosphonocrotonate via a Horner-Wadsworth-Emmons reaction to form 14 and 15. Crude reaction mixtures were subsequently hydrogenated and treated with excess methyl magnesium chloride to yield hydroxy indolizidine (18) and hydroxy quinolizidine (19) . Both product mixtures consisted of a 3:1 mixture of diastereomers, and the mass spectrum and retention time of the major (first eluting isomer) matched those of the hydrated natural alkaloids (Fig. and). Unfortunately, we were unable to separate the diastereomers using a range of LC methods and columns, so the products were analyzed by 2D NMR as mixtures (Fig. -S31; Table -S5). This led to complete assignments of both isomers for 18 and 19, with the major isomer in both samples exhibiting a clear ROESY correlation between the two stereogenic methines, indicating a syn orientation. This was supported by the lack of a ROESY correlation between the same methines for the minor isomer (anti orientation).