Further Probing the Properties of a Unique Sponge-derived Alkaloid Through the Isolation of a New (-)-(5E)-(8R)-(14Z)-Mycothiazole Analogue

Scale-up isolation of (+)-(5Z)-(8S)-(14Z)-mycothiazole (1) from Vanuatu specimens of C. mycofijiensis to semisynthesize (+)-(5Z)-(8S)-8-O-acetyl-(14Z)-mycothiazole (2) revealed a new diastereomer, (-)-(5E)-(8R)-(14Z)-mycothiazole (4). The structure of 4 was determined using HRMS, NMR, and comparing optical rotation to (-)-(5Z)-(8R)-(14Z)-mycothiazole (3) and 2. The maximum tolerated dose of 2 in mice was 0.1 mg/kg. The IC50 of 4 in PANC-1 and HepG2 cancer cell lines was 111.6 and 115.0 nM. Evaluation of 4 in C. elegans showed similar oxygen consumption compared to 1-2, and all compounds significantly increased the lifespan. The Z orientation at Δ5,6 is crucial for picomolar cytotoxicity but not for mitochondrial inhibition.

Reinvestigation of Mycothiazole Reveals the Penta-2,4-dien-1-ol Residue Imparts Picomolar Potency and 8S Configuration

Reinvestigation of mycothiazole (1) revealed picomolar potency (IC50 = 0.00016, 0.00027, 0.00035 μM) against pancreatic, (PANC-1), liver (HepG2), and colon (HCT-116) tumor cell lines. Reevaluation of 1 provided [α]D data indicating Vanuatu specimens of C. mycofijiensis contain the 8S enantiomer of 1 and not the 8R configuration previously reported. Semisynthesis provided 8-O-acetylmycothiazole (2), 8-oxomycothiazole (8), mycothiazole nitrosobenzene derivatives (MND1, MND2: 9a, 9b), and MND3 (10) with IC50 = 0.00129, >1.0, >1.0, >1.0, >1.0 μM, respectively, against PANC-1 cell lines. These results highlight the significance of the penta-2,4-dien-1-ol residue as a key structural feature of 1 required for its cytotoxicty against tumor cell lines.

Synthesis of Sultones from Chlorosulfates by a Complex Cascade Reaction Occurring under Mild Thermal Conditions

Chlorosulfate derivatives are interesting reagents that have been traditionally used to get other sulfur-containing compounds by formal nucleophilic substitution of the chlorine atom. This work describes a different mode of reactivity of alkyne-containing chlorosulfates to get sultones, the sulfur analogues of lactones. The complex skeletal rearrangement observed in this transformation is comparable to those intricate processes promoted or catalyzed by organometallic compounds. However, the reaction here described does not require any reagent or additive, being just a thermal process. Computational calculations support a mechanism based on a series of cascade reactions where almost every step is counterintuitive. Some of these steps include original processes related to classical reactions, thus adding complementary views to traditional organic chemistry.

Total Synthesis of the Potent HIF-1 Inhibitory Antitumor Natural Product, (8R)-Mycothiazole, via Baldwin-Lee CsF/CuI sp(3)-sp(2)-Stille Cross-Coupling. Confirmation of the Crews Reassignment

A convenient asymmetric total synthesis of the potent HIF-1 inhibitory antitumor natural product, (-)- or (+)-(8R)-mycothiazole (1), is described. Not only does our synthesis confirm the 2006 structural reassignment made by Crews ( Crews , P. , et al. J. Nat. Prod. 2006 , 69 , 145 ), it revises the [α]D data previously reported for this molecule in MeOH from -13.7° to +42.3°. The newly developed route to (8R)-1 sets the C(8)-OH stereocenter via Sharpless AE/2,3-epoxy alcohol reductive ring opening and utilizes two Baldwin-Lee CsF/cat. CuI Stille cross-coupling reactions with vinylstannanes 8 and 3 to efficiently elaborate the C(1)-C(4) and C(14)-C(18) sectors.

The marine sponge metabolite mycothiazole: a novel prototype mitochondrial complex I inhibitor

A natural product chemistry-based approach was applied to discover small-molecule inhibitors of hypoxia-inducible factor-1 (HIF-1). A Petrosaspongia mycofijiensis marine sponge extract yielded mycothiazole (1), a solid tumor selective compound with no known mechanism for its cell line-dependent cytotoxic activity. Compound 1 inhibited hypoxic HIF-1 signaling in tumor cells (IC(50) 1nM) that correlated with the suppression of hypoxia-stimulated tumor angiogenesis in vitro. However, 1 exhibited pronounced neurotoxicity in vitro. Mechanistic studies revealed that 1 selectively suppresses mitochondrial respiration at complex I (NADH-ubiquinone oxidoreductase). Unlike rotenone, MPP(+), annonaceous acetogenins, piericidin A, and other complex I inhibitors, mycothiazole is a mixed polyketide/peptide-derived compound with a central thiazole moiety. The exquisite potency and structural novelty of 1 suggest that it may serve as a valuable molecular probe for mitochondrial biology and HIF-mediated hypoxic signaling.