6,6'-Dihydroxythiobinupharidine, one of the several hemiaminals recently isolated from Nuphar, possesses activity against human pathogenic fungi. This finding, along with the discovery of the similar activity of synthetically derived deoxynupharidine a-thiohemiaminals, has led us to extend our search for other Nuphar hemiaminals. The C30 thiaspiran hemiaminals previously studied belonged to the thiobinupharidine and thionuphlutine B stereochemical families. This paper reports the detection, isolation, and structure determination of the hemiaminals of the neothiobinupharidine family. Both 6- (1) and 6'-hydroxyneothiobinupharidine (2) were isolated from extracts of Nuphar luteum of Polish origin. The presence of infrared Bohlmann bands, hydroxyl groups reduced by sodium borodeuteride, and the appearance of the pairs of peaks at m/e 230 and 228 and 178 and 176 in the mass spectrum indicated the dual hemiaminal-amine nature of each of the two alkaloids. The 1H NMR signals at δ 4.57 given by the one isomer and at δ 4.08 given by the other demonstrated that the hemiaminal hydroxyl was located at a C-6 or C-6' position. On sodium borodeuteride reduction, singly labeled neothiobinupharidines were formed, that from the C-6 hemiaminal giving m/e 179 but that from the C-6' hemiaminal giving m/e 178. The absence of the C-6 axial proton and the appearance of the C-6 equatorial proton as a singlet in the 1H NMR indicated the presence of an axial deuterium at C-6 in neothiobinupharidine-6-d1. Similar evidence indicated that the deuterium atom in neothiobinupharidine-6'-d1 was axial also. The CD of both hemiaminals in acid gave negative bands, the one from the C-6 hemiaminal appearing at 295 nm, and the one from the C-6' hemiaminal appearing at 279 nm.