Furofuranone Lignans from Leucophyllum ambiguum

Abstract

Eight furofuranone lignans with an endo,endo relationship between the oxygen atoms, an exo,exo relationship between the aryl groups, and a chair,chair conformation (1−4 and 6−9), in addition to the α-amino acid (3S)-hydroxy-3′,4′-dimethoxy-L-phenylalanine (5), veratric acid (10), and β-sitosterol (11), were isolated from the powdered and defatted airdried aerial parts of Leucophyllum ambiguum. Four of these lignans, ciquitins A−D, 1−4, were isolated for the first time as natural products. The structures of these compounds were established based on their spectrometric/spectroscopic data. Additionally, single-crystal X-ray crystallography confirmed the structure of ciquitin A (1), and derivatization with (9S)-naproxen and X-ray diffraction crystallography data established its absolute configuration. Ciquitins A (1) and B (2) possess a 9-hydroxy group; this chemical characteristic grants these species conformational isomerism not seen in the other six lignans. The conformers of 1 and 2 are distinguishable via their 1 H and 13 C NMR spectroscopic data. This is the first report of this phenomenon, and hence, a complete assignment of the signals in both spectra of each conformer for each compound is presented. Compounds 1−9 were found to exhibit potent inhibitory activity in the 1.0 × 10 −3 to 2.2 μM range against acetylcholinesterase, an enzyme directly involved in the etiology of Alzheimer's disease and senile dementia. Thus, these natural products are promising agents that are potentially useful for the treatment of neurological degeneration.

Lignans and Flavonoids from Cajanus cajan (L.) Millsp. and Their α‐Glucosidase Inhibitory Activities

“…Though coupling constants could not be clearly seen from peak splitting at H-8 and H-8', they could be deduced from splits at H-7 (J = 8.7) and H-7' (J = 8.6), the large coupling constants suggested the relationships between H-7 and H-8, H-7' and H-8' were both trans. [11] H-7 and H-8' were sterically close assumed from their correlation found at NOESY. Thus, its relative configuration which was the same as that of compound 1 was solved by HÀ H coupling constants combined with cross-peaks of NOESY.…”

“…1 H‐NMR and 13 C‐NMR spectra showed similar data (Table 1) as those of compound 1 , except for the differences at chemical shifts of the butyrolactone [ δ H 4.52 (d, J =8.7, 1H, H‐7), 5.07 (d, J =8.6, 1H, H‐7′), 2.55‐2.61 (m, 1H, H‐8), 3.29‐3.33 (m, 1H, H‐8′), 3.44‐3.54 (m, 2H, H‐9, 9′); δ C 82.5 (C‐7), 81.3 (C‐7′), 53.6 (C‐8, 8′), 60.1 (C‐9), 173.9 (C‐9′)], which suggested that compound 2 was also a dibenzylbutyrolactone lignan but with a different configuration or conformer. Though coupling constants could not be clearly seen from peak splitting at H‐8 and H‐8′, they could be deduced from splits at H‐7 ( J =8.7) and H‐7′ ( J =8.6), the large coupling constants suggested the relationships between H‐7 and H‐8, H‐7′ and H‐8′ were both trans [11] . H‐7 and H‐8′ were sterically close assumed from their correlation found at NOESY.…”

“…& Bonpl. [11] Compound 3 was yellow amorphous powder, from its quasi-molecular ion peak at m/z 515.1526 [M + H] + (calc. [C 26 H 27 O 11 ] + m/z 515.1548) on HR-ESI-MS, its molecular formula was indicated as C 26 H 26 O 11 , thus an unsaturation degree of 14 was calculated.…”

“…The different NMR data between the two conformers might be caused by different torsions of their two benzene rings, which were also found in major and minor conformers of ciquitin A and B isolated from Leucophyllum ambiguum Humb. & Bonpl [11] …”

Non-Alkaloid Cholinesterase Inhibitory Compounds from Natural Sources

“…Phenolic compounds from natural sources have shown anticholinesterase activity in several studies [ 34 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 ]. Phenolic compounds whose anticholinesterase activities have been reported are given in the Supplementary Material ( Table S2 ).…”