97(P-10) Pandanus属植物含有新規ピロリジン型アルカロイドの構造決定とバイオミメティック全合成(ポスター発表の部)

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The genus Pandanus belonging to the family Pandanaceae comprises about 600 species, which distribute widely in tropical and subtropical regions. Several Pandanus species are recognized as medicinal plants. Recently, a new skeletal type of alkaloids possessing a γ-alkylidene-α, β-unsaturated γ-lactone or γ-alkylidene-γ, β-unsaturated γ-lactam moiety has been isolated from Pandanus amaryllifolius. Since the Pandanus plants are potentially valuable as candidates for new medicinal resources, we have started chemical studies of Pandanus plants. Isolation and Structure Characterization of Two New Pandanus Alkaloids From the alkaloidal fraction, which was prepared by conventional procedure from an ethanol extract of the fresh leaves of P. amaryllifolius from Thail market, two new alkaloids, pandamarilactonine-A (1) and ?B (2), could be isolated together with a known compound, pandamarilactone-1 (3). By the spectral analysis (UV, IR, MS, 1D and 2D-NMR), the structures of two new compounds have been elucidated except for the stereochemistry of the vicinal asymmetric center at C-14 and C-15 positions. Then, PFG J-HMBC 2D method was applied with a combination of differential NOE experiments to establish the relative stereochemistry at C-14 and C-15 in 1 and 2 (Figure 4). From these data, we propose that pandamarilactonine-A (1) has erythro and pandamarilactonine-B (2) has threo structures. Biomimetic Total Synthesis of Pandamarilactonine-A (1) and -B (2) The biosynthetic route of new Pandanus alkaloids was assumed as shown in Figure 5. We planned a total synthesis of 1 and 2, which mimics the final stage of the biosynthesis proposed above (Figure 6). The key symmetrical amine, which corresponded to the hypothetical biogenetic intermediate, was prepared from benzylamine (10) via 6 steps sequence. Thus obtained crude amine was treated with a catalytic amount of TFA in CH_3CN to give pandamarilactonine-A (1) and -B (2) in 13% and 11% yield, respectively, which were identical with the natural products. Thus, we succeed in the first and biomimetic total synthesis of new alkaloids. Optical Purity of Natural Pandamarilactonine-A (1) and -B (2) Natural (1) exhibited [α]_D^<23>+35.0 (c 4.37, CHCl_3); on the contrary, the specific rotation of natural (2) was almost zero. We were interested in the optical purity of these natural products. With the synthetic racemate in hand, we examined the resolution of the enantiomers using chiral column chromatography. As a result, it was found that natural (1) contained dominantly the (+)-enantiomer in the ratio of 63:37 (Figure 7), while natural (2) existed as a racemate.
天然有機化合物討論会の論文
2000-10-01

97(P-10) Pandanus属植物含有新規ピロリジン型アルカロイドの構造決定とバイオミメティック全合成(ポスター発表の部)

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