A new unstable base, C15H21ON (I) was isolated from the root of Nuphar japonicum DC., and designated as dehydro-deoxynupharidine. It formed a crystalline perchlorate, m.p. 159~161°, (α)D +130.1° (CHCl3) (Anal. Calcd. for C15H22O5NCl: C, 54.28; H, 6.69; N, 4.22. Found: C, 54.19; H, 6.77; N, 4.41). The infrared spectrum of the perchlorate in chloroform showed bands at 877, 1510 and 3128 cm-1 attributable to the furan ring, and at 1640 cm-1 due to the iminium salt which conjugates with the furan ring, while its nuclear magnetic resonance spectrum contained three signals (δ 8.09, 7.56, 6.82), each corresponding to one proton, which were obviously attributable to the furan ring. Sodium borohydride reduction of the perchlorate of I afforded an oily amine, II, b.p. 125° (oil bath temp.), [α]p -114.1° (CHCl3), IR νmax^liquid 2764, 2792 (trans-quinolizidine) 874, 1032, 1505, 3140 cm-1 (furan). It formed a perchlorate, m.p. 203~204.5° (Anal. Calcd. for C15H24O5NCl: C, 53.49; H, 7.18; N, 4.16. Found: C, 53.58; H, 7.33; N, 4.11), and a picrate, m.p. 154.5~155.5° (Anal. Calcd. for C15H23ON·C6H3O7N3: C, 54.54; H, 5.67; N, 12.12. Found: C, 54.68; H, 5.67; N, 12.27). I was identical with an authentic specimen and No. 11 of (-)-deoxynupharidine1,2) (III) by the mixed melting point determination of the perchlorates and by the comparison of the infrared spectra of the free bases. The action of sodium borohydride on I, as expected, also reduced to form (-)-deoxynupharidine (II). These results suggest that dehydro-deoxynupharidine is represented by the formula (I). Furthermore, its correctness was confirmed by a synthesis as shown in the following schema: (±)-1,7-Dimethyl-octahydro-4H-quinolizinone (V) derived from an amino acid ester3 which forms a picrolonate, m.p. 156~158°, was condensed with ethyl 3-furoate to afford M. M was converted to an enamine (M) which forms a perchlorate, m.p. 145.5~147° (Anal. Calcd. for C15H22O5NCl: C, 54.28; H, 6.69; N, 4.22. Found: C, 54.45; H, 6.78; N, 4.19). The infrared spectra of the perchlorates of the synthetic (U) and the natural (I) bases, both in chloroform solution, were completely indistinguishable. Since the absolute configuration4 of (-)-deoxynupharidine (II) is known, structure (I) represents the structure and the absolute configuration of dehydro-deoxynupharidine.