Echinopines A (1) and B (2), novel sesquiterpenoids with an unprecedented rearranged skeleton named echinopane, were isolated from the roots of Echinops spinosus. The structures were elucidated by extensive spectroscopic analysis. The relative configuration of 1 was assigned by a combination of NOESY correlations and a simulation analysis. A plausible biosynthetic pathway for echinopane was discussed.

No abstract

The specific enzymological route of L-phenylalanine biosynthesis has not been established in any higher plant system. The possible pathway routes that have been identified in microorganisms utilize either phenylpyruvate or L-arogenate as a unique intermediate. We now report the presence ofarogenate dehydratase (which converts L-arogenate to L-phenylalanine) in cultured-cell populations of Nicotiana silvestris. Prephenate dehydratase (which converts prephenate to phenylpyruvate) was not detected. Arogenate dehydratase was also found in washed spinach chloroplasts, and these data add to emerging evidence in support of the existence in the plastidial compartment of a complete assembly of enzymes comprising aromatic amino acid biosynthesis. Arogenate dehydratase from tobacco and spinach were both specific for L-arogenate, inhibited by L-phenylalanine, and activated by L-tyrosine. Apparent K. values for L-arogenate (0.3 x 10-3 M), pH optima (pH 8.5-9.5), and temperature optima for catalysis (32-340C) were also similar.The current understanding of the post-prephenate pathways of phenylalanine and tyrosine biosynthesis and of their regulation has depended almost entirely upon a large base of comparative data from both prokaryotic and eukaryotic microorganisms (1). Until recently it had been assumed that higher plants utilize phenylpyruvate and 4-hydroxyphenylpyruvate as biosynthetic precursors of L-phenylalanine and L-tyrosine, respectively. A similar assumption prevailed for microorganisms until 1974, when enzymatic formation of L-arogenate from prephenate and enzymatic conversion of L-arogenate to L-tyrosine was first recognized in cyanobacteria (2). Since then, the arogenate pathway to L-tyrosine has been demonstrated in mung bean (3), corn (4), sorghum (5), tobacco (6), spinach (7), and buckwheat (J. L. Rubin and R.A.J., unpublished data). Prephenate dehydrogenase activity has not been found in any plant system, except in the developmental stage of seed germination in mung bean. Hence, the arogenate pathway appears to be the major, if not exclusive, mode of L-tyrosine biosynthesis in higher plants.Progress with the phenylalanine pathway has been slower, largely because ofthe technical difficulty ofthe enzyme assay (8,9). Fig. 1 (Binghamton, NY). The background and characteristics of the cell line ANS-1 of N.silvestris have been described (6). Suspension cultures of these cells were maintained by 1:4 dilution every 8 days into fresh medium. In this subculture routine, the cells undergo a lag phase of "'36 hr followed by a period of exponential growth that lasts until about day 6, when the cells enter a stationary phase.Cells were harvested in late-exponential phase between days 4 and 5 on Miracloth filters and were washed three times with 3% (wt/vol) mannitol. Excess wash solution was removed with the aid of a suction filter. The cell pack was frozen in liquid nitrogen and stored at -80'C or was ground in liquid nitrogen using a Waring blender and stored as a frozen powder at -80'C.Preparation of Partially...

Abstract:The structures and stereochemistry of 14 taxanes isolated from Taxus cunadensis have been rigorously established by high-resolution NMR techniques and mass spectrometry. Taus canadensis is the only yew that accumulates 9-dihydro-13-acetylbaccatin 111 (also called 7,9-deacetylbaccatin VI) as the most abundant taxane. Five 9-dihydrotaxanes derived from the Canadian yew are novel natural products not reported in the needles of other species of yew (8-11, 14, Fig. 1).