New Bis-Iridoids from Dipsacus laciniatus

Abstract

ABsmcr.-In addition to the known mono-and bis-iridoid glucosides loganin 1107, sweroside 161, cantleyoside 197, and sylvestrosides III lirl and IV 187, D i p s m lan'niatrrr has provided six new bis-iridoid glucosides, laciniatosides I-VI. These derivatives contain an acidic unit (secologanic acid, swerosidic acid, or 7deoxyloganic acid) and an alcoholic unit (various loganin-like alcohols) linked by an ester bond. Laciniatosides I 111, I1 127,III 137, IV 147, and VI 1117, as well as sylvestroside IV, were characterized by chemical transformations and 'Hand 13Cnmr spectroscopy. NOe measurements were used to determine the steric position of the hydrogens and substituents. Conformational analysis ofthe separated loganin-type subunit ofthe new compounds was performed using molecular mechanics calculations. The calculated structures were related to solution structures based on direct comparison of measured and calculated vicinal proton-proton coupling constants.The first bis-iridoid compound, cantleyoside 191, containing a secoiridoid unit and an iridoid unit, was found in Cantleya cornicukzta (1). Five other bis-iridoids related to cantleyoside, namely sylvestrosides I-IV from Dipsacus sylvestris (2), and laciniatoside V 151 from Dipsacus laciniatus L. (Dipsacaceae) ( 3 ) , were isolated previously. Recently, we have isolated five new bis-iridoids, laciniatosides I-IV 11-41 and laciniatoside VI 1111, from D. laciniatus. Here we report the isolation and the structure determination of laciniatosides I-IV and laciniatoside VI as well as the elucidation of the stereostructure of sylvestroside IV 181 which was not given by Jensen et al. (2). RESULTS AND DISCUSSIONThe above-ground parts of D. laciniatus L. were extracted and gave, after purification, a glycosidic fraction. Countercurrent distribution and cc were used to separate laciniatosides I 111, I1 121,l I11 131, IV 141, and V 151, sweroside 167, and sylvestrosides I11 13 and IV 181 from this fraction. Likewise, cantleyoside 191, loganin 1101, sylvestroside IV, sweroside, and laciniatoside VI {llf were isolated from the roots of the same plant.On the basis of 'H-and 13C-nmr data, a bis-iridoid structure was postulated for laciniatoside I 111. Its 13C-nmr spectrum (Table 1) also contained all the signals corresponding to secologanic acid and reported previously for unit A of sylvestrosides I11 13 and IV 181 (2). Two sets of signals for unit B, with slightly different intensity ratios, were observed in the n m r spectra of 1, recorded in several solvents; thus compound 1 occurs in solution as a mixture of two isomers. The nmr spectra gave no evidence for unsaturation in unit B. Acetylation of laciniatoside I 111 gave apentaacetyl derivative suggesting a hydroxyl group in unit "B." The signal of the C-4 atom of the pentaacetylated derivative showed an upfield shift of 3.6 ppm when compared to that of the same atom in laciniatoside I. This shift is in agreement with the presence of the hydroxyl group at C-3 position. The structure of laciniatoside I 111 (Scheme 1) was pr...

Phytochemicals and Biological Activities of Dipsacus Species

“…Compounds 38 -40 exist in iridoid form, which were isolated from the roots of D. asper (Table). Among them, compound 38, another common constituent, was also obtained from the roots of D. japonicus [61], the aerial parts of D. laciniatus [28] [63], and the seeds of D. sylvestris [64]. The roots of D. japonicus also afforded compound 39 [61].…”

“…The bis-iridoids 41 -57, which possess a secoiridoid unit together with an iridoid unit, are common in genus Dipsacus. Laciniatoside VI (41), occurring in D. laciniatus, displays a novel skeleton which was formed by rearrangement of the secologanin unit via ring opening at the C(1)ÀO(2) bond, followed by ring closure between C(7) and O(2) [63]. Compounds 42 -58 contain a,b-unsaturated ester moieties attached to enol ethers in iridoid pyran rings.…”

“…Compounds 47 -50 constitute a series of ethylidene ethers [35]. Investigation of the aerial parts of D. laciniatus led to the isolation of compounds 52, 53 and 55, which have a 3-oxo-iridoid unit [63], as compound 54 from D. ferox. Compounds 56 and 57, which carry a OH group at C(3), were obtained from D. laciniatus [63] and D. asper [35], respectively.…”

“…Investigation of the aerial parts of D. laciniatus led to the isolation of compounds 52, 53 and 55, which have a 3-oxo-iridoid unit [63], as compound 54 from D. ferox. Compounds 56 and 57, which carry a OH group at C(3), were obtained from D. laciniatus [63] and D. asper [35], respectively. Laciniatoside III (58) isolated from the aerial parts of D. laciniatus is the only compound with two iridoid units [63], and compound 59, which was obtained from the roots of D. asper [35] [28].…”

“…Compounds 56 and 57, which carry a OH group at C(3), were obtained from D. laciniatus [63] and D. asper [35], respectively. Laciniatoside III (58) isolated from the aerial parts of D. laciniatus is the only compound with two iridoid units [63], and compound 59, which was obtained from the roots of D. asper [35] [28]. Caffeoylquinic acids (CQAs), 68 -74, isolated from the roots of D. asper (Table), were produced via formation of ester bond(s) between the COOH group(s) of caffeic acid(s) and the OH group(s) of quinic acid.…”