Total Synthesis and Bioactivity Profile of (+)-Ieodomycins A and B and their Stereoisomers

Herein, we report the first- and second-generation syntheses of (+)-ieodomycins A and B and their stereoisomers via the late-stage elaboration of their conjugated E-diene side chains. Key steps for successful synthesis included Keck asymmetric allylation to introduce a hydroxyl group at the C5 position, consecutive Wipf's carboalumination modification, iodination, Sharpless asymmetric dihydroxylation, one-carbon homologation via cyanation, Mukaiyama lactonization, and Stille cross-coupling to form the conjugated E-diene moiety. Further, the preliminary in vitro bioactivity profile against various disease-related molecular targets and cell lines was investigated. Results indicated that compounds 30b and 30c, diastereoisomers of (+)-ieodomycin B (2), serve as α-glucosidase inhibitors, while compounds 30b and 30d inhibit the angiotensin-converting enzyme.

Studies of the Enantiocontrolled Synthesis of the C(10)-C(25) Subunit of Amphidinolide C

A stereocontrolled synthesis of 28, the C(10)-C(25) component of amphidinolide C (1), has been efficiently achieved. Reaction of the dithiane component 21 with nonracemic bis(epoxide) 19 directly affords functionalized 2,5-trans-disubstituted tetrahydrofuran 22. Propargylation is highly diastereoselective for the formation of the desired C(12)-C(13) anti stereochemistry, and the resulting terminal alkyne 25 is utilized for a regioselective syn-silylstannylation. A general strategy is illustrated for sequential replacement of stannyl and silyl substituents of the trisubstituted alkene to yield (E)-alkenyl iodide 28.

Asymmetric copper-catalyzed conjugate additions of organometallic reagents in the syntheses of natural compounds and pharmaceuticals

Access to enantiopure complex molecular structures is crucial for the development of new drugs as well as agents used in crop-protection. In this regard, numerous asymmetric methods have been established. Copper-catalyzed 1,4-additions of organometallic reagents are robust C-C bond formation strategies applicable in a wide range of circumstances. This review analyses the syntheses of natural products and pharmaceutical agents, which rely on the application of asymmetric Cu-catalyzed conjugate additions of various organometallic reagents. A wide range of available organometallics, e.g. dialkylzinc, trialkylaluminum, Grignard, and organozirconium, can now be used in conjugate additions to address various synthetic challenges present in targeted natural compounds. Furthermore, efficient catalysts allow high levels of stereofidelity over a diverse array of starting Michael acceptors.

Enantioselective total synthesis of (+)-ieodomycin A, (+)-ieodomycin B, and their three stereoisomers

Enantioselective routes for the total synthesis of ieodomycins A & B, and three stereochemical analogues of ieodomycin B via a late-stage elaboration of the side chain.

Asymmetric Baeyer-Villiger oxidation: classical and parallel kinetic resolution of 3-substituted cyclohexanones and desymmetrization of meso-disubstituted cycloketones

Classical kinetic resolution, parallel kinetic resolution and desymmetrization were achieved by asymmetric BV oxidation of 3-substituted and meso-disubstituted cycloketones.

Regioselectivity is a crucial issue in Baeyer–Villiger (BV) oxidation. To date, few reports have addressed asymmetric BV oxidation of 3-substituted cycloketones due to the high difficulty of controlling regio- and stereoselectivity. Herein, we report the asymmetric BV oxidation of 3-substituted and meso-disubstituted cycloketones with chiral N,N′-dioxide/Sc(iii) catalysts performed in three ways: classical kinetic resolution, parallel kinetic resolution and desymmetrization. The methodology was applied in the total and formal synthesis of bioactive compounds and natural products. Control experiments and calculations demonstrated that flexible and adjustable catalysts played a significant role in the chiral recognition of substrates.

Cs2CO3-promoted methylene insertion into disulfide bonds using acetone as a methylene source

An efficient halogen-free Cs2CO3-promoted methylene insertion into disulfide bonds has been achieved using acetone as a methylene source under mild conditions. This method provides a convenient and practical route to dithioacetals in up to 96% yield with good functional group compatibility.

α-Pyrones, secondary metabolites from fungus Cephalotrichum microsporum and their bioactivities

Cephalotrichum microsporum (SYP-F 7763) was a fungus isolated from the rhizosphere soil of traditional Chinese medicine Panax notoginseng. The EtOAc extract of Cephalotrichum microsporum cultivated on sterilized moistened-rice medium was separated by various chromatographic techniques, which yielded 11 metabolites (1-11) of this fungus. On the basis of the widely spectroscopic data, the chemical structures of isolated metabolites were determined, most of which were α-pyrones, including 5 compounds (4-7, and 10) unreported. In the anti-bacterial bioassay, compound 1 displayed significant inhibitory effects on three pathogenic bacteria, MR S. aureus, S. aureus, and B. cereus. α-Pyrones 2, 3, and 5-7 also displayed moderate inhibitory effects on MR S. aureus, S. aureus, and B. subtilis, which could be the major anti-bacterial constituents of Cephalotrichum microsporum. Additionally, compounds 1, 4, and 5 displayed significant cytotoxicity on five human cancer cell lines, with the IC₅₀ values < 20 μM, which are more effective than positive control 5-fluorouracil. Therefore, α-pyrones were important secondary metabolites of Cephalotrichum microsporum, which displayed anti-bacterial and anti-tumor activities.

Zirconium-Catalyzed Asymmetric Carboalumination of Unactivated Terminal Alkenes

Carbometalation of alkenes with stereocontrol offers an important opportunity for asymmetric C-C bond formation. However, the scope of catalytic stereoselective carbometalation of alkenes had until recently been limited to electronically biased alkenes or those with the presence of directing groups or other auxiliary functionalities to overcome the challenge associated with regio- and stereoselectivity. Catalytic asymmetric carbometalation of unactivated alkenes on the other hand remained as a formidable challenge. To address this long-standing problem, we sought to develop Zr-catalyzed asymmetric carboalumination of alkenes (namely, ZACA reaction) encouraged by our discovery of Zr-catalyzed alkyne carboalumination in 1978. Zr-catalyzed methylalumination of alkynes (ZMA) shows high regioselectivity and nearly perfect stereoselectivity. Its mechanistic studies have revealed that the ZMA reaction involves acyclic carbometalation with "superacidic" bimetallic reagents generated by interaction between two Lewis acids, i.e., alkylalanes and 16-electron zirconocene derivatives through dynamic polarization and ate complexation, affectionately termed as the "two-is-better-than-one" principle. With the encouraging results of Zr-catalyzed carboalumination of alkynes in hand, we sought to develop its alkene version for discovering a catalytic asymmetric C-C bond-forming reaction by using alkylalanes and suitable chiral zirconocene derivatives, which would generate "superacidic" bimetallic species to promote the desired carbometalation of alkenes. However, this proved to be quite challenging. Three major competing side reactions occur, i.e., (i) β-H transfer hydrometalation, (ii) bimetallic cyclic carbometalation, and (iii) Ziegler-Natta polymerization. The ZACA reaction was finally discovered by employing Erker's (-)-(NMI)₂ZrCl₂ as the catalyst and chlorinated hydrocarbon as solvent to suppress the undesired side reactions mentioned above. The ZACA reaction has evolved as a powerful tool for the efficient preparation of a wide range of chiral natural products through the following methodological developments: (1) three mutually complementary protocols for methyl-branched chiral alkanols; (2) water, MAO, and IBAO as promoters to accelerate otherwise sluggish carboaluminations; (3) one-step homologation synthesis of deoxypropionates based on one-pot ZACA-Pd-catalyzed vinylation tandem process; (4) ZACA-lipase-catalyzed acetylation-transition-metal-catalyzed cross-coupling processes for preparing various virtually enantiopure chiral alcohols; (5) the chemoselective ZMA and ZACA reactions as well as alkyne elementometalation-Pd-catalyzed cross-coupling for constructing a variety of chiral compounds containing regio- and stereodefined substituted alkenes; (6) the ZACA reaction of dienes to generate chiral organocyclic compounds including those with all-carbon quaternary stereocenters.

Base-promoted annulation of α-hydroxy ketones and dimethyl but-2-ynedioate: straightforward access to pyrano[4,3-a]quinolizine-1,4,6(2H)-triones and 2H-pyran-2,5(6H)-diones

A novel direct synthesis of pyrano[4,3-a]quinolizine-1,4,6(2H)-triones and 2H-pyran-2,5(6H)-diones from α-hydroxy ketones and dimethyl but-2-ynedioate via a base-promoted cascade annulation has been developed.

Total synthesis of (-)-doliculide, structure-activity relationship studies and its binding to F-actin

Actin, an abundant protein in most eukaryotic cells, is one of the targets in cancer research. Recently, a great deal of attention has been paid to the synthesis and function of actin-targeting compounds and their use as effective molecular probes in chemical biology. In this study, we have developed an efficient synthesis of (-)-doliculide, a very potent actin binder with a higher cell-membrane permeability than phalloidin. Actin polymerization assays with (-)-doliculide and two analogues on HeLa and BSC-1 cells, together with a prediction of their binding mode to F-actin by unbiased computational docking, show that doliculide stabilizes F-actin in a similar way to jasplakinolide and chondramide C.