We have recently reported the presence of new lupinine ester alkaloids, (-)-(trans-4'-hydroxycinnamyl)lupinine (1) and its derivatives (2-5) in the fresh seedlings of Lupinus luteus [1-4]. It has also been ascertained in our laboratory that 1 was formed from (-)-lupinine and trans-4-hydroxycinnamic acid by two enzymatic systems in Lupinus seedlings in the presence of ATP and CoA [5]. A new glucosidic lupin alkaloid, (-)-trans-4'-β-D-glucopyranosyloxy-3'-methoxycinnamyl)lupinine (6), has now been isolated from the fresh seedlings of L. luteus. 3 is known as a metabolite in the same young plant [6], but has never been obtained before as its glucoside. The structure of 6 was determined by spectrometric (MS and NMR) data and by direct comparison with a synthetic sample, prepared as described in the Experimental. NMR spectra showed that both the natural and synthetic samples of 6 were present as a mixture of trans and cis-isomers in the ratio of ca 3:2, respectively. The conversion of trans-cinnamates into the cis-isomers is unavoidable [1-4]. No detectable amount of 6 was found in the immature and mature seeds of L. luteus. However, its concentration increased rapidly during the first 3-10 days growth of seedlings, analogously to those of 1-5. In the later stages of the plant's growth, the concentration of 6 diminished and it again became a minor component.