Wim J. Baas

Naturally occurring seco-ring-A-triterpenoids and their possible biological significance

Abstract The literature appearing up to mid 1984 on the isolation and identification of naturally occurring seco -ring-A triterpenoids is reviewed. The distribution of these triterpenoids in the plant kingdom is discussed. Their biological action is considered in relation to plant protection. It is concluded that ring-A fission is a general process in the oxidative degradation of tetra- and pentacyclic triternoids.

Leaf wax of Lactuca sativa and Plantago major

Abstract Wax layers of plants are able to accumulate semivolatile organic compounds (SOCs) from the atmosphere. In this study, the composition of the leaf cuticular waxes of lettuce ( Lactuca sativa ) and common plantain ( Plantago major ) was determined for future studies on the role of cuticular waxes in the uptake and bioaccumulation of SOCs. In addition, to find a suitable extraction solvent to be used in these studies, the extraction efficiency of several solvents for the cuticular wax of the plants was studied. Leaf wax of L. sativa consists mainly of long-chain linear alcohols and minor amounts of fatty acids, while the major components of leaf wax of P. major are the free polar triterpene acids, oleanolic and ursolic acid, and the linear alkanes C 27 H 56 C 33 H 58 . The wax composition of both species only slightly changes with leaf developmental stage. This property makes them highly suitable as test plants in studies on uptake of SOCs. The waxes of both plant species are readily extractable with chloroform, toluene and dichloromethane. A mixture of chloroform and methanol 2:1 additionally extracted internal lipids and chlorophyll and, therefore, is not suitable. The apolar solvent, n -hexane, did not extract the triterpene acids of P. major . However, this solvent readily extracted the relatively apolar leaf wax of L. sativa . Since the extraction of SOCs (also from deeper embedded wax layers) can only be efficient if all the components of the cuticular wax are removed, we recommend to test the extraction efficiency of the solvent for each plant species beforehand.

The composition of phytosterols, latex triterpenols and wax triterpenoids in the seedling of Euphorbia lathyris L.

Abstract In the etiolated seedling of Euphorbia lathyris L., three groups of triterpenoids were found, located at different sites. The extracted triterpenoids were purified by TLC and HPLC and identified by GC/MS. Latex consisted mainly of triterpene alcohols. From these, guimarenol, 24-CH3-lanosterol and hopenol-B were not earlier identified in E. lathyris. The epicuticular wax contained mainly triterpene ketones, which were identified as taraxeron, hopenone-I, hopenone-II, hopenone-B, 3-oxo-22-hydroxyhopane, simiarenone and fernenone. Other components of the epicuticular wax were triterpenols, n-alkanes and aliphatic alcohols. The phytosterols were identified as cholesterol, campesterol, stigmasterol, sitosterol and isofucosterol.

Dihydronyctanthic acid methyl ester and other 3,4-seco-pentacyclic triterpenoids from Hoya lacunosa

Abstract From the wax of old leaves of Hoya lacunosa was isolated a mixture of 4(23)-saturated seco -ring-A triterpene acid methyl esters. One of these compounds was identified as the β-amyrin derivative 5-isopropyl-10(2-methoxy-carbonylethyl)-des-A-olean-12-en (dihydronyctanthic acid methyl ester), while another compound was a taraxerol derivative 5-isopropyl-10(2-methoxycarbonylethyl)-des-A-olean- 14-en. Two other constituents were probably derived from α-amyrin and taraxasterol, respectively.

Triterpene Composition of Hoya australis Cuticular Wax in Relation to Leaf Age

Summary Cuticular wax, collected at random from either young or old leaves of Hoya australis R. Br. ex Traill. , contains about 10 % free alcohols that is composed of five main compounds. Of these two were identified as the triterpenols lupeol and β -amyrin. In the wax from young leaves lupeol was the main free alcohol. With increasing leaf age gradually increasing concentrations of an unknown compound were found, up to as much as 90 % of the total alcohol fraction in three-year-old leaves. Experiments using 2- 14 C-mevalonic acid as a precursor indicate that this compound is a terpenol which is probably derived from β -amyrin.

The composition of the lipid constituents of Ilex aquifolium L. (Aquifoliaceae) in relation to the age of the leaf. I: The leaf wax

With increasing age of the leaf the chloroform-soluble part of the surface wax changes from a rather apolar composition largely constituted of a homologous series of hexyl esters of high molecular, saturated fatty acids (C22\3-C32) to a more polar composition with the triterpenol a-amyrin as the major component. Saturated long-chain hydrocarbons start to accumulate during leaf extension, whereas the major triterpenol accumulation occurs on full-grown leaves from the end of the first year of development. Minor concentrations of triterpenes are present on very young leaves with β-amyrin and β-amyrone as major components instead of the corresponding α-compounds.

3,4-Seco-triterpenoid acids and other constituents of the leaf wax of Hoya naumanii

Abstract The main GC-detectable constituents of a methylated extract of Hoya naumanii leaf wax are n -hydrocarbons ( ca 25%, mainly n -C 31 , and n -C33), the triterpenols β-amyrin, lupeol and α-amyrin ( ca 50% of the total wax), and the derived 3,4- seco -3-oic acid methyl esters: dihydronyctanthic acid, dihydrocanaric acid and dihydroroburic acid ( ca 20%). In the non-methylated wax these ring-A-fissioned triterpenoids occur almost exclusively in the form of free acids.

Investigations on Hoya species. IV. Leaf Phenolics and Leaf-Wax Triterpenes of Hoya australis R. BR. ex TRAILL in Relation to Leaf Age*

Summary Hoya australis leaves contain large amounts of chlorogenic acid, smaller amounts of iso-chlorogenic acid and other phenolic depsides such as p-coumaric acid ester and small concentrations of the apigenin-type f lavones. Anthocyanins were found only in very young leaves. With increasing leaf age the concentrations of chlorogenic- and isochloroagenic acid decreased; a more or less stable level was reached at the moment when anthocyanins could no longer be detected and when the concentration of the triterpene lupeol in the leaf wax began to increase.

Investigations on Hoya species, II. Latex Lipids and Leaf Phenolics of Hoya bella Hook

Abstract In Hoya bella latex a number of triterpenols were found, both in the free form and as esters. The main triterpenols were β-amyrin, cycloartenol, lupeol and the rarely occurring isobauerenol; esters of these alcohols which included cinnamic acid, propionic acid and isovaleric acid were identified. A homologous series of alkanes with carbon chain length ranging from C-20 to C-31 was found. In leaf extracts acylated flavonol glycosides as well as free ferulic acid occurred; the concentration of the latter decreased with increasing leaf age.

Isolation of a new seco-nor-Triterpenol from Hoya australis leaf wax

Abstract From the alcohol fraction of the epicuticular leaf wax of Hoya australis R. Br. ex Traill, a new triterpenol was isolated which, according to mass spectral and NMR data, is assumed to be A-seco-A-nor-⊿12-oleanenol.