Triterpenoid Skeleton Research Articles

ChemInform Abstract: A Diene Transmissive Diels—Alder Strategy for Oxygenated Nor‐Steroid and Triterpenoid Skeletons.

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A Diene Transmissive Diels−Alder Strategy for Oxygenated Nor-Steroid and Triterpenoid Skeletons

A diene transmissive cycloaddition strategy for the synthesis of tetracyclic skeletons is described. Initially both l-gulonolactone and l-arabinose were converted independently to related acetal aldehydes 13 and 14. A pentadienyl indium reagent supplied the triene unit for 16. The cis-isopropylidene acetal controlled the initial intramolecular [4 + 2] cycloaddition to the decalin 21, and a second (tandem) intermolecular cyclization afforded highly oxygenated nor-steroid and triterpenoid skeletons as chiral nonracemic compounds.

1998 Alfred Bader Award Lecture Tangents and targets: The synthetic highway from natural products to medicine

Synthetic studies directed toward various classes of compounds including taxoids and enediyne systems are described. These investigations include tether-controlled imtramolecular Diels-Alder reactions, carbometallation routes to dienes and furans, the use of carbohydrate building blocks, pentadienyl indium reagents for tandem cycloadditions to steroid and triterpenoid skeletons, and the synthesis of taxamycins and revolveneynes and related cyclophanes.Key words: cycloaddition, taxoids, enediyne, cyclophanes, carbometallation.

Studies on Physicochemical Behaviors of Glycyrrhizinate

Dipotassium β-glycyrrhizinate (GK2), contained in “Kanzou” root, with two hydrophilic sugarparts and one hydrophobic triterpenoid part is a three-based acid used as an anti-allerugic and anti-inflammatory drug in pharmaceuticals and soaps. The physicochemical features and behavior of GK2 and derivatives (GK2s) have been but little studied. To use GK2s effectively, the physicochemical characteristics of GK2s, interactions with an artificial membrane model and catalytic activity toward nonionic ester surfantant (NES), a solubilizing agent, must be studied. GK2s characteristically form anionic micelles depending on pH and structure of the hydrophobic triterpenoid skeleton. GK2 micelles deliver certain cationic drugs into hydrophobic membranes, particularly so at less than pH 5.5. GK2s catalyze the hydrolysis of NES. Pharmaceutically undesirable acidic catalysis by GK2s is due to the presence of carboxy groups that are not protonated in its structure. The catalytic activity of GK2 was found completely inhibited by an equimolar amounts of cyclodextrins (CyDs) such as γ-CyD owing to the formation of host-guest complexes. Both GK2 and NES are formed in pharmaceuticals at the same time. The adsorption of GK2 at 340nm was found useful for determining the microenviroment of the enone chromophore of GK2s.

Early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry

The distribution of triterpanes in sediments and crude oils is commonly used for oil/oil and oil/source rock correlation in petroleum geochemistry while isomer ratios of such compounds are applied as maturity parameters. The triterpane pattern in terrestrially influenced geological samples is, however, remarkably less diverse than the triterpenoid skeletons occurring in the extant higher plant biosphere. Natural observations, laboratory experiments and molecular mechanics calculations have revealed that acid catalysed double bond isomerization and skeletal rearrangement reactions of terrigenous triterpenoids during early diagenesis are the key to understanding the triterpane patterns in more matured geological materials. Examples studied in detail are the double bond isomerization of oleanenes and the subsequent hydrogenation of the products into oleanane and 18α-oleanane, and the transformation of taraxer-14-ene and lup-20(29)-ene into oleanenes. Although the reactions are likely to be kinetically controlled, the main products formed and ultimately preserved are the thermodynamically most stable ones. The experimental results and natural observations have significant implications for the use of terrigenous triterpenoid compounds in petroleum geochemistry.

Baccharane (18,19-secolupane): A rare triterpenoid skeleton widespread in Triassic sediments and petroleum from the Adriatic Basin

Baccharane (18,19-secolupane) 1, a triterpenoid skeleton seldom encountered in living organisms, has been characterized together with 17βH-des- E-lupane 2, one of its minor degradation products, in Italian Triassic sediment and crude oil samples from the Adriatic Basin by synthesis of standards. Reports of baccharane-derived triterpenoids in the field of natural products are scant and up to now restricted to terrestrial plants (angiosperms and ferns). In this regard, sedimentary baccharane derivatives may indicate a continental contribution (ferns?) to fossil organic matter; but they may also represent a contribution of as yet undetermined marine microorganisms, as has been proposed for dammarenes and dammaranes. Alternatively, they could be the bio/geochemical transformation products of biosynthetically closely related precursors such as lupane- or dammarane-type triterpenoids. The apparently restricted occurrence of baccharane derivatives in geological samples (up to now detected only in Triassic sediments of the Adriatic Basin) confers upon these compounds great value as correlation parameters and possibly as source indicators.

Raspacionin B, a Further Triterpenoid from the Mediterranean Sponge Raspaciona aculeata

A new triterpenoid, raspacionin B [4], has been isolated from the Mediterranean sponge Raspaciona aculeata. The structure and relative stereochemistry of 4 were elucidated by means of spectral methods, mainly 1D and 2D nmr. The absolute stereochemistry was proposed by comparison of its cd curve with those of related compounds. The triterpenoid skeleton of raspacionin B, characterized by the presence of a cyclopropane ring, is related to those of terpenoids co-occurring in the same sponge

Two‐dimensional NMR study of ganwuweizic acid

AbstractSeveral two‐dimensional NMR techniques were applied to assign completely the 1H and 13C chemical shifts and to study the configuration and conformation of a new triterpenoid, 3‐keto‐9,10,19‐cyclopropyllanost‐24‐en‐26‐oic acid (ganwuweizic acid). Some 13C NMR signals previously reported for the triterpenoid skeleton were corrected.

The diagenetic fate of taraxer-14-ene and oleanene isomers

The extractable organic matter in Holocene to early Miocene deep-sea sediments from Site 645 (ODP Leg 105) in Baffin Bay contains almost exclusively biological markers of terrigenous origin. Pentacyclic triterpenoids of the α-(ursene) and β-amyrin (oleanene) type often occur as the most abundant compounds in the aliphatic hydrocarbon, ketone and alcohol fractions of the sediment extract. A specific diagenetic reaction involves the conversion of taraxer-14-ene into olean-12-ene in the upper 700 metres of the sedimentary sequence. The taraxerene-to-oleanene conversion is complete before the onset of isomerisation of diasterenes at C-20. In the sediment as well as in laboratory simulation experiments, olean-12-ene further isomerises to olean-13(18)-ene and olean-18-ene, the latter of which may be the direct precursor of 18β(H)- and 18α(H)-oleanane found in sediments containing more mature organic matter and in crude oils. The subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid.

Crystal and molecular structure of adiantol B bromoacetate

The crystal structure of adiantol B bromoacetate, C31H51O2Br, has been determined by a three-dimensional X-ray analysis. The crystals are monoclinic, a= 19·138, b= 7·437, c= 9·849 Å, β= 94° 04′, Z= 2, space group P21. The intensities were measured with a Hilger and Watts automatic four-circle diffractometer using Mo-Kα radiation. The structure was solved by the programme SEARCH, for the automatic heavy-atom analysis, and refined by full-matrix least-squares calculations to a final R of 0·076 for 1570 independent observed reflexions. The absolute configuration was determined by the anomalous dispersion method. The rings A, B, C, and D of the triterpenoid skeleton have a chair form, and ring E is represented by the α-envelope conformation. The configuration at C(21) was S-form.