Two new quinolizidine alkaloids, 13-epi-hydroxysparteine [1] and desoxyangustifoline [2], have been isolated from the hitherto uninvestigated species Thermopsis mongolica. Also, (+)-sparteine, 17-oxosparteine, 5,6-dehydrolupanine, α-isolupanine, (+)-hydroxysparteine, (-)-anagyrine, (-)-thermopsine, (-)-cytisine, and N-methylcytisine have been found. The genus Thermopsis (Fabaceae) includes some 18 species (1), among which 9 are found in Mongolia. The species investigated so far contain quinolizidine alkaloids, including some anagyrine-type toxins. Extracts of some species have been used in folk medicine as expectorants (1).From the aerial parts of Mongolian Thermopsis mongolica Czefr., the following eleven compounds were isolated and identified on the basis of spectral data and some chemical transformations. Nine are the known alkaloids (+)-sparteine, 17-oxosparteine, 5,6-dehydrolupanine, α-isolupanine, (+)-13-hydroxysparteine, (-)-anagyrine, (-)-thermopsine, (-)-cytisine, and N-methylcytisine. The remaining two compounds, 13-epi-hydroxysparteine [1] and desoxyangustifoline [2], are new alkaloids.The eims of 1, m/z 250 {M}+ and fragments m/z 233 {M - 17}+, 137, and 98, was identical with that of (+)-13-hydroxysparteine, but the two differed in their Rf values. The epimerization of the hydroxyl group in the latter (2) yields a compound whose ms and tlc are identical with those of 1. To determine the position of H-11, (+)-13-hydroxysparteine was dehydrogenated with mercuric acetate and subsequently rehydrogenated to give two 13-hydroxy-α-isosparteine isomers: 13-α-hydroxy-α-isosparteine and 13-β-hydroxy-α-isosparteine (3). The ms of these compounds corresponded to 13-hydroxysparteine. They differed from 1 by their Rf values. Thus, the structure of the new alkaloid, 13-epi-hydroxysparteine, was identified. This compound has hitherto not been known as a natural compound.The cims of 2 showed an ion with m/z 221 {M + 1}+, and the eims (70 eV) showed fragments m/z 220 {M}+, 179 {M - 41}+, and 98. The fragment at m/z 179 is formed upon C-11/C-14 bond cleavage, similar to the fragmentation of angustifoline and tinktorine (4,5). The fragment at m/z 98 arises from ring A following the fragmentation pattern of the sparteine-type alkaloids (6); hence, the structure of 2 is similar to that of angustifoline but without a carbonyl group.The ¹H-nmr spectrum of 2 exhibited signals for three vinylic protons at δ 5.78 (m, 1H, H-15), 5.07 (br d, J=17.5 Hz, 1H, H-16), and 5.02 (br d, J=9 Hz, 1H, H-16'); a peak at δ 3.75 (br, =NH) exchanged with D₂O. This spectrum also supported an angustifoline-like structure. An unambiguous proof of structure 2 was its cyclization into 13-epi-hydroxysparteine [1], carried out in a phosphate buffer (pH = 5.5) in the presence of HCHO (7). The latter was compared by ms and tlc with 13-epi-hydroxysparteine obtained after epimerization of 13-hydroxysparteine. Compound 1 and 4-α-hydroxysparteine, prepared from 4-α-hydroxylupanine after reduction with LiAlH₄ in THF, differed in their ms and Rf values. This excluded the possibility of an open A ring, i.e., a propylene chain at C-6 of a sparteine structure.