Towards the Synthesis of the 4,19-Diol Derivative of (-)-Mycothiazole: Synthesis of a Potential Key Intermediate

Asymmetric Catalytic Vinylogous Addition Reactions Initiated by Meinwald Rearrangement of Vinyl Epoxides

The first catalytic asymmetric multiple vinylogous addition reactions initiated by Meinwald rearrangement of vinyl epoxides were realized by employing chiral N,N'-dioxide/Sc^III complex catalysts. The vinyl epoxides, as masked β,γ-unsaturated aldehydes, via direct vinylogous additions with isatins, 2-alkenoylpyridines or methyleneindolinones, provided a facile and efficient way for the synthesis of chiral 3-hydroxy-3-substituted oxindoles, α,β-unsaturated aldehydes and spiro-cyclohexene indolinones, respectively with high efficiency and stereoselectivity. The control experiments and kinetic studies revealed that the Lewis acid acted as dual-tasking catalyst, controlling the initial rearrangement to match subsequent enantioselective vinylogous addition reactions. A catalytic cycle with a possible transition model was proposed to illustrate the reaction mechanism.

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.

Microwave-assisted organic acid–base-co-catalyzed tandem Meinwald rearrangement and annulation of styrylepoxides

A microwave-assisted acid and base co-catalyzed strategy shows very high efficiency in the tandem reaction for the conversion of styrylepoxides into [1,1′-biaryl]-3-carbaldehydes.

A Catalytic Approach for Enantioselective Synthesis of Homoallylic Alcohols Bearing a Z-Alkenyl Chloride or Trifluoromethyl Group. A Concise and Protecting Group-Free Synthesis of Mycothiazole

A protecting group-free strategy is presented for diastereo- and enantioselective routes that can be used to prepare a wide variety of Z-homoallylic alcohols with significantly higher efficiency than is otherwise feasible. The approach entails the merger of several catalytic processes and is expected to facilitate the preparation of bioactive organic molecules. More specifically, Z-chloro-substituted allylic pinacolatoboronate is first obtained through stereoretentive cross-metathesis between Z-crotyl-B(pin) (pin = pinacolato) and Z-dichloroethene, both of which are commercially available. The organoboron compound may be used in the central transformation of the entire approach, an α- and enantioselective addition to an aldehyde, catalyzed by a proton-activated, chiral aminophenol-boryl catalyst. Catalytic cross-coupling can then furnish the desired Z-homoallylic alcohol in high enantiomeric purity. The olefin metathesis step can be carried out with substrates and a Mo-based complex that can be purchased. The aminophenol compound that is needed for the second catalytic step can be prepared in multigram quantities from inexpensive starting materials. A significant assortment of homoallylic alcohols bearing a Z-F₃C-substituted alkene can also be prepared with similar high efficiency and regio-, diastereo-, and enantioselectivity. What is more, trisubstituted Z-alkenyl chloride moiety can be accessed with similar efficiency albeit with somewhat lower α-selectivity and enantioselectivity. The general utility of the approach is underscored by a succinct, protecting group-free, and enantioselective total synthesis of mycothiazole, a naturally occurring anticancer agent through a sequence that contains a longest linear sequence of nine steps (12 steps total), seven of which are catalytic, generating mycothiazole in 14.5% overall yield.

Palladium-Metalated Porous Organic Polymers as Recyclable Catalysts for the Chemioselective Synthesis of Thiazoles from Thiobenzamides and Isonitriles

Two types of thiazole derivatives are synthesized through a multistep cascade sequence with Pd-metalated phosphorus-doped porous organic polymers (POPs) as heterogeneous catalysts. The POPs could be used as both ligands and catalyst supports. No obvious aggregation and loss of any catalytic activity of the catalysts were observed after 10 runs of the reaction. More importantly, imidazo[4,5- d]thiazoles, which are a new class of thiazole derivatives, could be obtained through K₂CO₃-promoted intramolecular cyclization of the synthesized polysubstituted thiazoles. Furthermore, the in vitro anticancer activity of these new compounds were tested with MTT assay, and compound 4b exhibited good antitumor activity toward T-24 and A549 cells with IC₅₀ values of 10.3 ± 0.8 and 11.8 ± 0.5 μM, respectively. In addition, the action mechanism of 4b on tumor cells was determined.

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.