Peter L. Katavic

New Cytotoxic Norditerpenes from the Australian Nudibranchs Goniobranchus Splendidus and Goniobranchus Daphne

This study reports the isolation and characterisation of six new metabolites with ‘gracilin’-type carbon skeletons and of aplytandiene-3 from the Australian nudibranch Goniobranchus splendidus. The structure of gracilin G is revised, and the C-6 configuration deduced by comparison of calculated 3JC/H values with values measured using the EXSIDE pulse sequence. A lactone isolated from Goniobranchus daphne contains a rearranged spongionellin-type skeleton. Screening of selected metabolites revealed significant cytotoxicity against a HeLa S3 cell line by five of the new terpenes.

Oxygenated Terpenoids from the Australian Sponges Coscinoderma matthewsi and Dysidea sp., and the Nudibranch Chromodoris albopunctata

The isolation and structure elucidation of seven new oxygenated terpenoids and eight known terpene metabolites from marine invertebrates collected at the Inner Gneerings Reef, South East Queensland, is discussed. Investigation of the sponge Coscinoderma matthewsi yielded an epoxylactone derivative (1) of the known furanoterpene tetradehydrofurospongin-1 (2). A chemical investigation of the dissected nudibranch Chromodoris albopunctata provided the new oxygenated diterpenes 12α-acetoxyspongian-16-one (10), 20-acetoxyspongian-16-one (12), 20-oxyspongian-16-one propionate (13) and 12α,20-dioxyspongian-16- one dipropionate (14) in conjunction with three other known diterpene metabolites, while two new chromodorolides, D(17) and E(18), in addition to four known diterpenes were isolated from a Dysidea sp.

Tropane alkaloids from Darlingia darlingiana

A new γ-pyranotropane, darlingine N-oxide, was isolated from the bark and leaves of Darlingia darlingiana, along with the known compound, darlingine. 1D-NOESY NMR experiments indicated that the N-methyl groups of both alkaloids were orientated towards the pyran ring.

A versatile synthetic approach toward diversity libraries using monosaccharide scaffolds

The pyranose scaffold is unique in its ability to position pharmacophore substituents in various ways in 3D space, and unique pharmacophore scanning libraries could be envisaged that focus on scanning topography rather than diversity in the type of substituents. Approaches have been described that make use of amine and acid functionalities on the pyranose scaffolds to append substituents, and this has enabled the generation of libraries of significant structural diversity. Our general aim was to generate libraries of pyranose-based drug-like mimetics, where the substituents are held close to the scaffold, in order to obtain molecules with better defined positions for the pharmacophore substituents. Here we describe the development of a versatile synthetic route toward peptide mimetics build on 2-amino pyranose scaffolds. The method allows introduction of a wide range of substituent types, it is regio- and stereospecific, and the later diversity steps are performed on solid phase. Further, the same process was applied on glucose and allose scaffolds, in the exemplified cases, and is likely adaptable to other pyranose building blocks. The methods developed in this work give access to molecules that position the three selected binding elements in various 3D orientations on a pyranose scaffold and have been applied for the production of a systematically diverse library of several hundred monosaccharide-based mimetics.

Chemoecological studies on marine natural products: terpene chemistry from marine mollusks

Abstract Some species of nudibranchs (Mollusca) protect themselves from predatory attacks by storing defensive terpene chemicals acquired from dietary sponges (Porifera) in specialized body parts called MDFs (mantle dermal formations), often advertising their unpalatability to potential predators by means of bright coloration patterns. Consequently, the survival of these trophic specialist species is closely related to the possibility of obtaining the defensive tools from sponges that live in their immediate vicinity; therefore, it is important to determine as precisely as possible the chemical composition of nudibranch extracts prior to any ecological studies addressing issues that involve their alimentary behavior and their defensive strategies, including the significance of their color patterns. Some of our recent studies on the chemical composition of terpene extracts from nudibranchs belonging to the genera Chromodoris and Hypselodoris are summarized. We also report the development of a method to assay extracts and purified metabolites for their feeding deterrent activity against co-occurring generalist predators. In a recent chemoecological study, showing that repugnant terpene chemicals are accumulated at extremely high concentrations in exposed parts of the nudibranchs’ bodies, the feeding deterrence assays were carried out on the generalist marine shrimp Palaemon elegans, very common in the Mediterranean. We have modified this assay for use with the Australian shrimp species P. serenus, and confirmed the ecological validity of the assay by analysis of extracts from species of sponges and mollusks that live in the same habitat as P. serenus. The deterrent properties of haliclonacyclamine alkaloids isolated from the sponge Haliclona sp. were demonstrated, with the alkaloid mixture demonstrating palatability deterrence at concentrations as low as 0.05 mg/mL, and complete deterrence at 0.75 mg/mL. In contrast, the diterpene thuridillin metabolites from the sacoglossan mollusk Thuridilla splendens did not deter feeding by P. serenus.

Orthogonally Protected Monosaccharide Building Blocks for Solid Phase Production of Diversity Oriented Libraries

The large scale synthesis of three orthogonally protected monosaccharide scaffolds suitable for use in the solid phase preparation of large diversity libraries is presented. Scaffolds based on 2-amino-2-deoxy-d-glucopyranose, 2-amino-2-deoxy-d-allopyranose, and 2,4-diamino-2,4-dideoxy-d-galactopyranose were prepared in good yield and with minimal chromatographic purification from commercially available methyl 2-azido-2-deoxy-1-thio-β-d-glucopyranose and methyl 2-amino-2-deoxy-1-thio-β-d-glucopyranose.

TWO NEW NAPHTHOQUINONES FROM THE ROOTS OF CONOSPERMUM SPHACELATUM

Two new naphthoquinones, 8-[(2′E)-3′,7′-dimethylocta-2′,6′-dienyl]-2,7-dihydroxynaphthalene-1,4-dione (1) and 2-hydroxy-6,7-dimethoxy-3-methylnaphthalene-1,4-dione (2), and one known naphthoquinone, (+)-teretifolione-B (3), were isolated from the roots of Conospermum sphacelatum Hook. (Proteaceae) collected in central Queensland. The structures of compounds (1) and (2) were determined by spectroscopic analysis.

Note of clarification about: Oxygenated Terpenoids from the Australian Sponges Coscinoderma matthewsi and Dysidea sp., and the Nudibranch Chromodoris albopunctata [vol. 65, pp. 531–538]

The isolation and structure elucidation of seven new oxygenated terpenoids and eight known terpene metabolites from marine invertebrates collected at the Inner Gneerings Reef, South East Queensland, is discussed. Investigation of the sponge Coscinoderma matthewsi yielded an epoxylactone derivative (1) of the known furanoterpene tetradehydrofurospongin-1 (2). A chemical investigation of the dissected nudibranch Chromodoris albopunctata provided the new oxygenated diterpenes 12?-acetoxyspongian-16-one (10), 20-acetoxyspongian-16-one (12), 20-oxyspongian-16-one propionate (13) and 12?,20-dioxyspongian-16-one dipropionate (14) in conjunction with three other known diterpene metabolites, while two new chromodorolides, D (17) and E (18), in addition to four known diterpenes were isolated from a Dysidea sp.