Structure elucidation of three triterpenoid saponins from Alphitonia zizyphoides using 2D NMR techniques

The genus Alphitonia Reissek ex Endl. (Rhamnaceae): A review of its customary uses, phytochemistry and biological activities

ETHNOPHARMACOLOGICAL RELEVANCE

Alphitonia Reissek ex Endl. is a relatively small genus of the family Rhamnaceae. Plants of this genus are found predominantly in the tropical regions of Southeast Asia, Australia and the Pacific, with some species being widely distributed and others endemic to a region. Almost half of the species of the Alphitonia genus have been reported for their customary (traditional and contemporary) medicinal uses. This includes for the treatment of skin conditions, headache, stomachache, inflammation, and body pain such as joint pain and childbirth.

AIM OF THE REVIEW

The aim of this review is to provide the first comprehensive account on the customary uses including ethnomedicinal uses, and phytochemistry and biological activities of the Alphitonia genus, and to identify gaps in current knowledge and scope for future research of plants of this genus.

MATERIALS AND METHODS

Information relevant to the genus Alphitonia was collected by searching the scientific databases (SciFinder, Google Scholar, ACS publications, PubMed, Wiley Online Library and International Plant name Index). Species names were validated using the World Flora Online database (www.worldfloraonline.org).

RESULTS

Eight plants from the Alphitonia genus have been reported to be used as customary medicines, i.e. A. excelsa, A. ferruginea, A. franguloides, A. incana, A. neocaledonica, A. petriei, A. philippinensis and A. zizyphoides. A. excelsa, A. petriei, A. philippinensis and A. zizyphoides, have been shown to have biological activities that align with their customary uses, including antimicrobial, antioxidant and anti-inflammatory activities. Only five Alphitonia species reported for their medicinal customary uses have been explored for their phytochemistry, i.e. A. excelsa, A. neocaledonica, A. petriei, A. philippinensis and A. zizyphoides. Compounds identified from these plants include those that are well known for their medicinal importance. A. macrocarpa, A. whitei and A. xerocarpus have also been examined for their phytochemistry and have been found to have the same or similar bioactive compounds to those found in customarily used Alphitonia species. No biological activities or phytochemistry studies have been reported for the known customarily used medicinal plants A. ferruginea, A. franguloides and A. incana.

CONCLUSIONS

This review highlights the customary uses, biological activities and phytochemistry of plants of the Alphitonia Reissek ex Endl. genus and highlights the significance of the knowledge systems of Indigenous peoples. Of the plants that have been researched for their biological activities and phytochemistry, there is good correlation with these properties and their customary medicinal uses. However, over half of the plants of the Alphitonia genus, including those that are already reported in the public domain for their customary medicinal uses, have had none or limited biological activities or phytochemistry studies conducted. While only eight species of the Alphitonia genus have been reported as customary medicines, other Alphitonia species also possess medicinally important compounds, and it is possible that they are customary medicines but their uses have not been shared publicly by the Indigenous knowledge custodians. There is clearly much scope for further investigation of this genus with regards to their ethnomedicinal uses and therapeutic potential.

Ultrafast acquisition of 1H-1H dipolar correlation experiments in spinning elastomers

We show that two widely used 2D solid-state NMR (ssNMR) pulse sequences can be implemented in an ultrafast (UF) manner, and yield 2D spectra of elastomers in a single scan, under magic-angle spinning. UF 2D ssNMR provides an acceleration of one to several orders of magnitude for classic experiments.

Triterpenoids from the leaves of Alphitonia xerocarpus Baill and their biological activity

Ten previously undescribed triterpenoid saponins and a previously undescribed norlupane triterpenoid were isolated, with three known saponins, four known flavonoids, two known lupane derivatives, sitosterol and 6'-heptadecanoyl-3-O-β-d-glucopyranosylsitosterol from the leaves of Alphitonia xerocarpus (Rhamnaceae), an endemic tree of New Caledonia. The chemical structures of the purified compounds were identified by nuclear magnetic resonance and mass spectrometry. The isolated compounds were tested for their antioxidant, antityrosinase, antibacterial and cytotoxic activity. The aqueous methanol extract showed antioxidant activity (DPPH assay) due to the presence of rutin. Ceanothenic acid showed good cytotoxic activity against a KB cell line (IC50 = 2.6 μM) and antibacterial activity against Staphylococcus aureus and Enterococcus faecalis with MIC values of 8 and 16 μg/mL, respectively. The previously undescribed 29-hydroxyceanothenic acid exhibited moderate cytotoxic activity (IC50 = 10 μM), good antibacterial activity against S. aureus (MIC = 4 μg/mL) and moderate antibacterial activity against E. faecalis (MIC = 16 μg/mL).

Ultrafast 2D NMR: an emerging tool in analytical spectroscopy

Two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy is widely used in chemical and biochemical analyses. Multidimensional NMR is also witnessing increased use in quantitative and metabolic screening applications. Conventional 2D NMR experiments, however, are affected by inherently long acquisition durations, arising from their need to sample the frequencies involved along their indirect domains in an incremented, scan-by-scan nature. A decade ago, a so-called ultrafast (UF) approach was proposed, capable of delivering arbitrary 2D NMR spectra involving any kind of homo- or heteronuclear correlation, in a single scan. During the intervening years, the performance of this subsecond 2D NMR methodology has been greatly improved, and UF 2D NMR is rapidly becoming a powerful analytical tool experiencing an expanded scope of applications. This review summarizes the principles and main developments that have contributed to the success of this approach and focuses on applications that have been recently demonstrated in various areas of analytical chemistry--from the real-time monitoring of chemical and biochemical processes, to extensions in hyphenated techniques and in quantitative applications.

Evaluation of some Samoan and Peruvian medicinal plants by prostaglandin biosynthesis and rat ear oedema assays

In our ongoing program to find new anti-inflammatory compounds, 58 extracts from 46 different medicinal plant species, used in treatment of inflammatory disorders-38 plants from the traditional medicine of Western Samoa and eight originating from the indigenous medicine of the Shipibo-Conibo tribe of Peruvian Amazonia-ere evaluated. The ability of all extracts to inhibit cyclooxygenase-1 catalysed prostaglandin biosynthesis in vitro was examined. Of the plant species tested 14 showed moderate to strong inhibition; including 11 Samoan and three Peruvian species. Further, 12 Samoan and all eight Peruvian species were investigated on their inhibitory activity of ethyl phenylpropiolate induced rat ear oedema in vivo. Significant activity was shown by 10 of the Samoan and by all eight Peruvian species. An additional evaluation of the most active species was provided through a compilation of existing literature documenting traditional medicinal uses, pharmacological activity and chemical constituents. Several known cyclooxygenase-1 inhibitors were reported to which the observed pharmacological activity can be attributed at least partly. The combination of chemical and pharmacological literature data and our experimental data may help to explain the anti-inflammatory use of these species in indigenous medicine.

Dammarane saponins from Zizyphus lotus

Four dammarane-type saponins were isolated by means of centrifugal partition chromatography from the root bark of Zizyphus lotus. Their structures were elucidated using a combination of 1D and 2D 1H and 13C NMR spectra and mass spectroscopy. One of these glycosides is the known jujuboside A. The others are three new dammarane saponins, identified as 3-O-beta-D-glucopyranosyl(1-->6)-beta-D-glucopyranosyl (1-->3)-[alpha-L-rhamnopyranosyl(1-->2)]-alpha-L-arabinopyranosyl jujubogenin = jujuboside C, 3-O-alpha-L-rhamnopyranosyl (1-->2)-[beta-D-glucopyranosyl(1-->3)]-beta-D-galactopyranosyl lotogenin = lotoside I, and 3-O-alpha-L-rhamnopyranosyl(1-->2)-[beta-D-glucopyranosyl (1-->3)]-beta-D-glucopyranosyl lotogenin = lotoside II. Lotogenin is a new dammarane derivative identified as (15R, 16R, 20R, 22R)-16 beta, 22-epoxydammar-24-ene-3 beta, 15 alpha, 16 alpha, 20 beta-tetraol.