Neostenanthera gabonensis (Engl. & Diels) Exell (Annonaceae) is a forest shrub or a small tree growing in West Africa, where it is used in local folk medicine (1). From two different samples of N. gabonensis, both collected in Ghana, we isolated the new alkaloids (-)-stenantherine [1] and (-)-N-methylstenantherine [2]. To our knowledge this is the first phytochemical study on a plant from the genus Neostenanthera (2). Stenantherine [1] was isolated as a main alkaloid from both plant samples. Its eims exhibits the molecular ion as base peak at m/z 327.14706 (C₁₉H₂₁NO₄) and intensive fragment ions at m/z 326 [M - H]⁺ and m/z 296 [M - OMe]⁺. In the uv spectrum (λ max 217, 274, 296 nm) a bathochromic shift upon addition of alkali indicates phenolic function(s). The ¹H nmr shows the characteristic features of a noraporphine alkaloid substituted by three "aromatic" methoxy groups (δ 3.74, 3.93, and 3.98 ppm) and one phenolic hydroxy group (δ 8.63 ppm); the chemical shifts and coupling constants of the three aromatic protons indicate that positions 1, 2, 3, and 11 of the noraporphine ring system are substituted. Since the ms of N,O-diacetylstenantherine [3] shows a significant loss of 32 mu (MeOH) from the molecular ion, one methoxy group has to be placed at C-3 (3). In the ¹³C nmr of 1 the resonances of the three methoxy carbons appear at δ 62.6, 61.4, and 60.4 ppm, respectively. These data exclude a methoxy group at C-11 (4) and establish structure 1 for (-)-stenantherine. (-)-N-Methylstenantherine [2] was found in trace amounts only. The spectra and the color reaction on tlc show close similarity to 1. Structure 2 was confirmed by N-methylation of 1, which yields a product identical with natural 2 (cd, co-tlc, ¹H nmr). In the ¹H nmr of O-acetyl-N-methylstenantherine [4] significant downfield shifts (in comparison with 1 and 2) of the three aromatic protons and a strong shielding (δ 3.44 ppm) of the methoxy group at C-1 are observed, whereas all other resonances remain practically unaffected. N. gabonensis is a rare plant in Ghana and, therefore, only scarce amounts of plant material were available for our investigations. The first plant collection contained stems exclusively. From this material only one further alkaloid was isolated besides 1 and 2 in trace amounts, and it was identified as the known nor-aporphine (-)-O-methylisopiline (5). The plant material of the second collection consisted of roots (60%) and stems (40%). Compounds 1 and 2 occurred in concentrations similar to those found in the first sample, but, in addition, eight further alkaloids were isolated and identified as the known aporphines (-)-liridinine (minor alkaloid), (-)-O-methylisopiline (minor alkaloid), O-methylmoschatoline (minor alkaloid), (+)-isopiline (major alkaloid), (+)-N-methylisopiline (trace), (+)-lirinidine (minor alkaloid), (+)-caaverine (trace) (5), and the proaporphine (-)-N-methylcrotsparine (6). Up to now the (+)-enantiomers of isopiline and N-methylisopiline are not reported in the literature. The co-occurrence of (-)- and (+)-aporphines in N. gabonensis might be of interest from a biogenetic point of view.