Pycnanthuquinone C, an Unusual 6,6,5-Tricyclic Geranyltoluquinone from the Western Australian Brown Alga Cystophora harveyi

Abstract

Chemical investigation of the Western Australian marine brown alga Cystophora harveyi resulted in the isolation of the new linearly fused 6,6,5-tricyclic compound pycnanthuquinone C (1), in addition to four previously reported geranyltoluquinol derivatives. Structures were elucidated by interpretation of spectrometric data. Compounds with the same cyclic skeleton as 1 have been reported to be useful drug leads for the treatment of type 2 diabetes, while compounds 4 and 7 are known constituents of Chinese medicinal herbs. A biosynthetic scheme encompassing all of the geranyltoluquinol derivatives isolated from C. harveyi is proposed.

Nature of the Intermediates in Gold(I)‐Catalyzed Cyclizations of 1,5‐Enynes

“…In general, good yields were obtained with electrophilic catalysts B or C. Enyne 9 n, substituted at the meta position of the aryl ring, led to a mixture of regioisomeric compounds 16 e and 16 e' ( [21] 1,5-Enyne 9 o reacted smoothly with catalyst B at room temperature to give cycloadduct 16 f in 95 % yield, the structure of which was confirmed by X-ray diffraction (Scheme 4). [22] Tricyclic compound 16 f possesses the tricyclic skeleton of (+)-pycnanthuquinone C (17), [23,24] which is a natural compound structurally related to pycnanthuquinones A and B [25] and rossinone. [26] Intermediates of cyclizations of 1,6-enynes have been trapped by intra- [27] or intermolecular cyclopropanation; [18,28] however, the trapping of intermediates 2 by alkenes in cyclizations of 1,5-enynes was unknown.…”

Meroterpenes from Marine Invertebrates: Structures, Occurrence, and Ecological Implications

“…The biosynthetic origin of these compounds has been largely speculated about; they clearly arise from corresponding derivatives with linear prenyl chains that are usually isolated concomitantly from the natural source. Ortho -prenylated quinones can undergo different chemical transformations, ranging from cascade cyclization reactions involving carbocation species [19] to pericyclic reactions, such as electrocyclizations or cycloadditions, via ortho -quinones methide intermediates [20]. However, with the data available, it is not possible to argue whether the above mentioned transformations occur in the organism, prior to its extraction, either enzymatically (in nature dehydrogenase enzymes appear to catalyze such processes [21]) or not, or that they take place during isolation and/or chromatographic purification.…”

Biomimetische Synthese von (−)‐Pycnanthuchinon C über eine Vinylchinon‐Diels‐Alder‐Reaktion

“…Die komplizierter aufgebauten Pycnanthuchinone A und B wurden in Pycnanthus angolensis, einem westafrikanischen Baum, der breite Anwendungen in der traditionellen afrikanischen Medizin findet, als antihyperglykämische Verbindungen gefunden. [6] Dagegen wurde für Pycnanthuchinon C, das nur in winzigen Mengen aus der Braunalge Cystophora harveyi isoliert werden konnte, keine biologische Aktivität berichtet. [7] Trotz einiger Versuche konnte die relative Konfiguration an C3 nicht aufgeklärt werden, sodass sich die absolute Konfiguration bisher nicht bestimmen ließ.…”

“…Zusätzlich konnte die Konfiguration des Isomers 13 aus der röntgenkristallographischen Analyse ermittelt werden, und die trans-Konfiguration des Hydrindan-Gerüsts war aus der Literatur bekannt. [5,6] Aufgrund dieser Daten waren zwei Isomere möglich: 16 und (À)-3 (Abbildung 3).…”

“…[5,6] Mit Zugang zu reichlich Material waren wir jedoch in der Lage, nOe-Signale zwischen den Protonen beider Hydroxygruppen und des Methinwasserstoffatoms an C6 in wasserfreiem [D 6 ]DMSO zu beobachten. Dies ist nur möglich, wenn das nichtnatürliche (À)-Pycnanthuchinon C die in Abbildung 3 gezeigte relative Konfiguration aufweist.…”