Fragmentation of Golgi membranes by norrisolide and designed analogues

Subcellular targeting strategies for protein and peptide delivery

Cytosolic delivery of proteins and peptides provides opportunities for effective disease treatment, as they can specifically modulate intracellular processes. However, most of protein-based therapeutics only have extracellular targets and are cell-membrane impermeable due to relatively large size and hydrophilicity. The use of organelle-targeting strategy offers great potential to overcome extracellular and cell membrane barriers, and enables localization of protein and peptide therapeutics in the organelles. Although progresses have been made in the recent years, organelle-targeted protein and peptide delivery is still challenging and under exploration. We reviewed recent advances in subcellular targeted delivery of proteins/peptides with a focus on targeting mechanisms and strategies, and highlight recent examples of active and passive organelle-specific protein and peptide delivery systems. This emerging platform could open a new avenue to develop more effective protein and peptide therapeutics.

Total Syntheses of Norrisolide-Type Spongian Diterpenes Cheloviolene C, Seconorrisolide B, and Seconorrisolide C

The first total syntheses of three unusual norrisolide-type rearranged spongian diterpenes, cheloviolene C, seconorrisolide B, and seconorrisolide C, have been accomplished via a common intermediate through late-stage ring-scissoring. The synthesis features a Wolff ring contraction for the synthesis of the trans-hydrindane system, and a crucial retro Diels-Alder reaction/intramolecular ene cyclization for the rapid stereoselective construction of the furo[2,3-b]furan system, which is commonly seen in rearranged spongian diterpenes.

Total Synthesis of (-)-Chromodorolide B By a Computationally-Guided Radical Addition/Cyclization/Fragmentation Cascade

The first total synthesis of a chromodorolide marine diterpenoid is described. The core of the diterpenoid is constructed by a bimolecular radical addition/cyclization/fragmentation cascade that unites two complex fragments and forms two C-C bonds and four contiguous stereogenic centers of (-)-chromodorolide B in a single step. This coupling step is initiated by visible-light photocatalytic fragmentation of a redox-active ester, which can be accomplished in the presence of an iridium or a less-precious electron-rich dicyanobenzene photocatalyst, and employs equimolar amounts of the two addends. Computational studies guided the development of this central step of the synthesis and provide insight into the origin of the observed stereoselectivity.

Spongian-16-one Diterpenes and Their Anatomical Distribution in the Australian Nudibranch Goniobranchus collingwoodi

Six new (1-6) spongian-16-one analogues have been characterized from the Australian nudibranch species Goniobranchus collingwoodi, along with four known spongian-16-one derivatives. The structures and relative configuration were suggested by spectroscopic analyses informed by molecular modeling. Dissection of animal tissue revealed that the mantle and viscera differ in their terpene composition. Whole body extracts were not toxic to brine shrimp (Artemia sp.), but were unpalatable to palaemon shrimp (Palaemon serenus) at a concentration found within the nudibranch. Individual terpenes were not cytotoxic to human lung (NCIH-460), colorectal (SW620), and liver (HepG2) cancer cells.

Isothiouronium modification empowers pyrimidine-substituted curcumin analogs potent cytotoxicity and Golgi localization

Most of protein post-translational modifications occur in the Golgi and many human diseases are associated with abnormal Golgi function or improper post translational modifications of proteins in the Golgi. In this study, we designed and synthesized 4 × 6 series of novel isothiouronium-modified (E,E)-4,6-bis(styryl)-pyrimidine analogs and found that they localized at the Golgi as visualized by the intrinsic fluorescence of the analogs. The isothiouronium-modified analogs had potent cytotoxicity in both normal (Chinese Hamster Ovary or CHO) and cancer cells. Furthermore, permethylated isothiouronium-modified analogs showed cancer cell-selective cytotoxicity. The molecular mechanisms underlying Golgi localization of isothiouronium-modified compounds were investigated using 7 CHO and 4 human cancer cell lines and the results indicated that the compounds had binding partners in the Golgi. Thus, isothiouronium-modified analogs might be promising anticancer agents, novel Golgi staining reagents, and useful research tools for studying Golgi functions in normal or cancer cells and in Golgi-related human diseases.

Rearranged Diterpenes and Norditerpenes from Three Australian Goniobranchus Mollusks

Three new norditerpenes (1, 6, and 7) and four diterpenes (2-5) with extensively rearranged carbon skeletons have been characterized from Australian nudibranchs. The relative configuration of the cyclopropyl-containing verrielactone (1) from Goniobranchus verrieri was suggested by spectroscopic analysis at 500 MHz informed by a combination of molecular modeling and DFT calculations. The nudibranchs G. splendidus and G. cf. splendidus provided 2-7, for which the structures and stereochemistry were deduced by 2D NMR studies at either 500 or 700 MHz. Each of the seven terpenoids exhibited a carbon skeleton modified from one of the tetrahydroaplysulphurin, spongionellin, or gracilane series of terpenes. A biosynthetic pathway to terpenes 1-7 from spongialactone is proposed.

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.

7,9-Diaryl-1,6,8-trioxaspiro[4.5]dec-3-en-2-ones: readily accessible and highly potent anticancer compounds

7,9-Diaryl-1,6,8-trioxaspiro[4.5]dec-3-en-2-ones are a recently described group of spirocyclic butenolides that can be generated rapidly and as a single diastereomer through a cascade process between γ-hydroxybutenolides and aromatic aldehydes. The following outlines our findings that these spirocycles are potently cytotoxic and have a dramatic structure-function profile that provides excellent insight into the structural features required for this potency.

Exploring the Chemistry of Marine Opisthobranchs: Recent Results

The current communication is an extended abstract of the presentation delivered on the joint Moldo-Italian seminar “New frontiers in natural product chemistry”, held in the Institute of Chemistry, Academy of Sciences of Moldova on 30th September. An overview of the recent studies conducted by our group on opisthobranch molluscs from distinct geographical areas is briefly presented.

Golgi-modifying properties of macfarlandin E and the synthesis and evaluation of its 2,7-dioxabicyclo[3.2.1]octan-3-one core

Golgi-modifying properties of the spongian diterpene macfarlandin E (MacE) and a synthetic analog, t-Bu-MacE, containing its 2,7-dioxabicyclo[3.2.1]octan-3-one moiety are reported. Natural product screening efforts identified MacE as inducing a novel morphological change in Golgi structure defined by ribbon fragmentation with maintenance of the resulting Golgi fragments in the pericentriolar region. t-Bu-MacE, which possesses the substituted 2,7-dioxabicyclo[3.2.1]octan-3-one but contains a tert-butyl group in place of the hydroazulene subunit of MacE, was prepared by chemical synthesis. Examination of the Golgi-modifying properties of MacE, t-Bu-MacE, and several related structures revealed that the entire oxygen-rich bridged-bicyclic fragment is required for induction of this unique Golgi organization phenotype. Further characterization of MacE-induced Golgi modification showed that protein secretion is inhibited, with no effect on the actin or microtubule cytoskeleton being observed. The conversion of t-Bu-MacE and a structurally related des-acetoxy congener to substituted pyrroles in the presence of primary amines in protic solvent at ambient temperatures suggests that covalent modification might be involved in the Golgi-altering activity of MacE.

Chemical biology studies on norrisolide

The cellular activity of norrisolide (7), a novel Golgi-vesiculating agent, was dissected as function of its chemical structure. This natural product induces irreversible vesiculation of the Golgi membranes and blocks protein transport at the level of the Golgi. The Golgi localization and fragmentation effects of 7 depend on the presence of the perhydroindane core, while the irreversibility of fragmentation depends on the acetyl group of 7. We show that fluorescent derivatives of norrisolide are able to localize to the Golgi apparatus and represent important tools for the study of the Golgi structure and function.

Trifunctional norrisolide probes for the study of Golgi vesiculation

Inspired by the effect of norrisolide on the Golgi complex, we synthesized norrisolide probes that contain: the perhydroindane core of the parent natural product for Golgi localization, a crosslinking unit (aryl azide or epoxide) for covalent binding to the target, and a tag (biotin or iodine) for subsequent target purification. We found that biotin-containing probes 14, 20 and 24 induced inefficient Golgi vesiculation. However, the iodinated probe 25 induced extensive and irreversible Golgi fragmentation. This probe can be used for the isolation of the cellular target of norrisolide.

Synthesis of a 10,000-membered library of molecules resembling carpanone and discovery of vesicular traffic inhibitors

Split-and-pool synthesis of a 10,000-membered library of molecules resembling the natural product carpanone has been achieved. The synthesis features development of solid-phase multicomponent reactions between nitrogen nucleophiles, enones, and hydroxylamines, and a solid-phase application of the Huisgen cycloaddition affording substituted triazoles. The synthesis was performed in high-capacity (500 microm) polystyrene beads using a one bead-one stock solution strategy that enabled phenotypic screens of the resulting library. Using whole-cell fluorescence imaging, we discovered a series of molecules from the carpanone-based library that inhibit exocytosis from the Golgi apparatus. The most potent member of this series has an IC(50) of 14 microM. We also report structure-activity relationships for the molecules exhibiting this interesting phenotype. These inhibitors of exocytosis may be useful reagents for the study of vesicular traffic.

Norrisolide: Total Synthesis and Related Studies

A stereoselective synthesis of (+)-norrisolide is presented. This natural product belongs to a family of marine spongiane diterpenes the structure of which is characterized by a fused gamma-lactone-gamma-lactol ring system attached to a bicyclic hydrophobic core. Our studies led to the development of a expedient synthesis of such gamma-lactone-gamma-lactol motifs based on ring expansion of a fused cyclopropyl ester. Highlights of the synthetic strategy toward norrisolide include the coupling of the two bicyclic systems by constructing a sterically demanding C9-C10 bond and the installation of the C19 oxygen at the last step of the synthesis via a Baeyer-Villiger oxidation.