Total synthesis of (.+-.)-justicidin P. A new lignan lactone from Justicia extensa

Abstract

The total synthesis of (±)-justicidin P, a new lignan lactone from Justicia extensa (Acanthaceae), is described. Justicidin P exists at 25 °C as two rotamers, evidenced by proton NMR studies and confirmed by a theoretical calculation of the rotational barrier. Two other natural products, diphyllin and justicidin A, have also been synthesized.

Arylnaphthalide Lignans from Cleistanthus collinus

“…After 2 h the solvents were removed to yield the monomethyl ether 8 (5 mg). The spectral properties (IR, 1 H-NMR and MS) of the compound were identical to those reported 10) earlier for justicidine P. Preparation of (؎) Cleistanone [(؎) 1] from Diphyllin (2) A mixture of diphyllin (2, 20 mg) in CCl 4 (10 ml) containing NBS (20 mg) and AIBN (8 mg) was heated at 80°C for 3 h. The mixture was cooled and the solvent was removed under reduced pressure. The residue was dissolved in a mixture of MeOH and CH 2 Cl 2 (1 : 1, 20 ml) and was stirred for 3 h at room temperature.…”

“…The spectral properties ( 1 H-NMR and MS) of the latter were found to be similar to those reported for justicidine P. 10) Finally the preparation of cleistanone (1) (in racemic form) was achieved from diphyllin (2). The latter was treated 10) with N-bromosuccinimide (NBS) in the presence of azobisisobutyronitrile (AIBN) followed by subsequent treatment with MeOH. The product was identical in spectral properties ( 1 H-NMR and MS) with the natural cleistanone (1).…”

“…The existence of such rotamers was also previously noted for the structurally similar lignans, justicidin P 10) and phyllamyricins D and E. 9) Cleistanone (1) naphthalide lignans containing an alkoxy group on the lactone ring. 10) Previously only a few compounds of this group like justicidine P 10) and phyllamyricins D and E 9) were reported.…”

Chemical constituents and biological activities of species of Justicia: a review

“…For example, jusmicranthin (22) 25 °C as two rotamers (Wang & Ripka, 1983). Some arylnaphthalide lignans are glycosylated derivatives (32-37, 39, 42, and 49).…”

Six Lignans from Phyllanthus myrtifolius

“…Compound 1 had the molecular formula (C 23 H 2O O 8 ) as deduced by HREIMS, having an additional CH 2 O unit relative to that of phyllamyricin C ( 8 ) and the same as that of justicidin P ( 7 ) . The 1 H-NMR spectrum of 1 showed a close resemblance to that of 8 (Table ), with five aromatic protons constituted by two singlets (δ 8.23, 6.90) and an ABX system appearing between δ 6.77 and 6.96, an AB pattern for an OCH 2 O group (δ 6.04, 6.08, each d, J = 1.3 Hz), and three MeO singlets (δ 4.07, 3.99, 3.77).…”