Structure and Absolute Configuration of Helosides A and B, New Saponins from Chamaelirium luteum

Abstract

Investigation of Chamaelirium luteum roots led to the isolation of two new steroidal saponins, helosides A and B, that contain a previously unreported aglycone, helogenin. Their structures and absolute configuration were elucidated through MS-MS, NMR, chemical degradation, and X-ray crystallography.

Caco-2 Monolayer Permeability and Stability of Chamaelirium luteum (False Unicorn) Open-Chain Steroidal Saponins

“…Chamaelirosides A and B (1 and 2), which are based on the same aglycone skeleton, (23R,24S)chiograsterol B (3), were predominant. 35 Given the oral administration of false unicorn herbal extracts, it is important to evaluate bioavailability to identify which of these compounds, if any, are able to reach the bloodstream. Both metabolism and permeability across the gastrointestinal tract are significant barriers to oral bioavailability.…”

Revision of the Absolute Configurations of Bethosides B and C and Their Aglycone

“…1 Our recent investigation into the constituents of the medicinal plant Chamaelirium luteum (False Unicorn) resulted in the isolation of two steroidal saponins, helosides A and B (1 and 2, Figure 1). 2 These contain an unusual (22S,25R)-3β, 11R,16β, 22,26-pentahydroxy-cholest-5-ene skeleton (helogenin, 3), which lacks the additional rings derived from the C-17 side chain that are characteristic of furo-and spirostanol saponins. The stereochemistry of the side chain in 3 was determined to be (22S,25R) by X-ray crystallographic analysis.…”

“…The stereochemistry of the side chain in 3 was determined to be (22S,25R) by X-ray crystallographic analysis. 2 The closely related 3β,16β,22,26-tetrahydroxy-cholest-5-ene skeleton (6 is the 25R isomer), whose planar structure differs from 3 in lacking C-11 hydroxylation, has been reported as the aglycone in steroidal saponins isolated from Solanum lyratum and Solanum anguivi (Solanaceae), 3,4 Allium tuberosum (Alliaceae), 5 and Trillium erectum (Melanthiaceae). 6 Surprisingly, the 1 H and 13 C NMR spectroscopic data for the side chains of 1 and 2 were in good agreement with those for bethosides B and C isolated from T. erectum (4 and 5, Figure 1), despite the fact that we had deduced the latter to contain the epimeric 22R configuration in the side chain (Δδ H e 0.04 ppm, Δδ C e 0.3 ppm in C 5 D 5 N for positions 20 to 27 of the corresponding saponins, Table 1).…”

Open-chain steroidal glycosides, a diverse class of plant saponins

“…102,103 These all possess a single a-L-rhamnopyranosyl residue at C-16 of the aglycone that may be substituted by an acetyl group (at positions C-2, C-3, or both) and in some cases by either a 3,4,5-trimethoxybenzoyl or a para-methoxybenzoyl group (at position C-3). (Dd H ¼ 0.01 ppm; Dd C ¼ 0 ppm) 102,104 in particular strongly suggests that the 11a orientation is also present in 134, however the revision of 133 and 139 must necessarily be tentative since a chemical shi range only is reported for H-11 in these saponins. 102 Four open-chain steroidal glycosides have been reported possessing aglycones that are oxygenated at positions C-3, C-12, C-16, and C-22, namely spongioside B (146) isolated from Dioscorea spongiosa 18 and dioseptemlosides A, B, and I (147, 148, and 149, respectively) isolated from D. septemloba.…”

“…Typically, the absolute congurations of positions within the sidechain are assigned either by comparison of their 1 H and 13 C NMR chemical shis with those of closely related structures, or by degradation into known structural elements. One of the most reliable methods for determination of sidechain stereochemistry is X-ray crystallographic analysis, either of the naturally occurring glycoside 110 or aglycone, 27,51,104 or in combination with total synthesis. 118 The modied (or advanced) Mosher ester analysis has also been used to determine the absolute conguration of C-22 in some glycosides of the alliosterol family, 16,36,45,102,107 although this method suffers from problems of selectivity if more than one secondary alcohol is present in the aglycone.…”