Methoxymethyl-directed aryl metalation. Total synthesis of (.+-.)-averufin

Dynemicin A Derivatives as Potential Cancer Chemotherapeutics by Mutasynthesis

The enediyne antitumor antibiotics have remarkable structures and exhibit potent DNA cleavage properties that have inspired continued interest as cancer therapeutics. Their complex structures and high reactivity, however, pose formidable challenges to their production and development in the clinic. We report here proof-of-concept studies using a mutasynthesis strategy to combine chemical synthesis of select modifications to a key iodoanthracene-γ-thiolactone intermediate in the biosynthesis of dynemicin A and all other known anthraquinone-fused enediynes (AFEs). By chemical complementation of a mutant bacterial producer that is incapable of synthesizing this essential building block, we show that derivatives of dynemicin can be prepared substituted in the A-ring of the anthraquinone motif. In the absence of competition from native production of this intermediate, the most efficient utilization of these externally-supplied structural analogues for precursor-directed biosynthesis becomes possible. To achieve this goal, we describe the required Δorf15 blocked mutant and a general synthetic route to a library of iodoanthracene structural variants. Their successful incorporation opens the door to enhancing DNA binding and tuning the bioreductive activation of the modified enediynes for DNA cleavage.

Examining Heterodimerization by Aryl C-N Coupling in Dynemicin Biosynthesis

Distinct among the enediyne antitumor antibiotics, the dynemicin subgroup is comprised of two discrete halves, an enediyne and an anthraquinone, but each is ultimately derived from the same linear β-hydroxyhexaene precursor. The linkage of these two halves by an aryl C-N bond is examined here using a variety of experimental approaches. We demonstrate that this heterodimerization is specific for anthracenyl iodide as the corresponding bromo- and amino-substituted anthracenes do not support dynemicin biosynthesis. Furthermore, biochemical experiments and chemical model reactions support an S_RN1 mechanism for the aryl C-N coupling in which electron transfer occurs to the iodoanthracene, followed by loss of an anthracenyl iodide and partition of the resulting aryl radical between C-N coupling and reduction by hydrogen abstraction. An enzyme pull-down experiment aiming to capture the protein(s) involved in the coupling reaction is described in which two proteins, Orf14 and Orf16, encoded by the dynemicin biosynthetic gene cluster, are specifically isolated. Deletion of orf14 from the genome abolished dynemicin production accompanied by a 3-fold increased accumulation of the iodoanthracene coupling partner, indicating the plausible involvement of this protein in the heterodimerization process. On the other hand, the deletion of orf16 only reduced dynemicin production to 55%, implying a noncatalytic, auxiliary role of the protein. Structural comparisons using AlphaFold imply key similarities between Orf14 and X-ray crystal structures of several proteins from enediyne BGCs believed to bind hydrophobic polyene or enediyne motifs suggest Orf14 templates aryl C-N bond formation during the central heterodimerization in dynemicin biosynthesis.

Synthesis and in vitro biological evaluation of novel dendrocandin analogue as potential anti-tumor agent

Dendrocandins are characteristic chemical structures of D. officinale and have strong physiological bioactivities. In this study, a dendrocandin analogue (1) has been prepared by total synthesis (9 steps, 12.6% overall yield) in which coupling reaction and Wittig reaction as the key steps. Compound 1 was also evaluated for its anticancer activity in vitro against six human cancer cells (MCF-7, A549, A431, SW480, HepG-2 and HL-60) using MTT assays. Compound 1 showed potent cytotoxicity, with the IC50 value 16.27 ± 0.26 µM. The expression levels of apoptotic proteins indicated that compound 1 can up-regulate the expression of apoptotic proteins, leading to apoptosis. This compound suggested that it's potential as anticancer agent for further development.

Aryne-based strategy in the total synthesis of naturally occurring polycyclic compounds

This review has outlined the strategies and tactics of using arynes in the total syntheses of polycyclic natural products.

A concise synthesis of pawhuskin A

Pawhuskin A is an isoprenylated stilbene that was isolated from Dalea purpurea and reported to have affinity for the opioid receptor in vitro. It has been synthesized through a convergent sequence that joins a prenylated aldehyde with a geranylated phosphonate in a stereoselective Horner-Wadsworth-Emmons condensation to afford the target E olefin isomer. This synthesis confirms the structure assigned to the natural product and establishes a route that may be used to explore its biological activity and to prepare more active analogues.

Synthesis of the alkenyl-substituted tetracyclic core of the bisabosquals

HCl-catalyzed deprotection and cyclization of benzylic alcohol 15 cleanly provided tricycle 16 by a cis-selective intramolecular Diels-Alder reaction. Acetylation of the phenol, bis epoxidation, and base-catalyzed hydrolysis and cyclization afforded tetracycle 19 with the bisabosqual skeleton, but the wrong stereochemistry at the tertiary alcohol. Selective dehydration of the tertiary alcohol to form the exocyclic alkene, ozonolysis, reductive deoxygenation of the side chain epoxide, and addition of MeMgBr to the ketone from the less hindered face gave tertiary alcohol 24 with the tetracyclic core of bisabosqual A (1).

An Improved Method for the Bromination of Metalated Haloarenes via Lithium, Zinc Transmetalation: A Convenient Synthesis of 1,2-Dibromoarenes

A facile protocol for the synthesis of 1,2-dibromoarenes is described. A standard ortho-lithiation/bromination procedure, when applied to bromoarenes, resulted in poor yields of the corresponding 1,2-dibromoarenes (13-62% yield). However, transmetalation of the transient aryllithium intermediate to an arylzinc species with ZnCl2, followed by bromination, resulted in dramatically improved yields of the synthetically useful 1,2-dibromoarenes (68-95% yield).

Synthesis and structure-activity studies of schweinfurthin B analogs: Evidence for the importance of a D-ring hydrogen bond donor in expression of differential cytotoxicity

The synthesis and biological evaluation of several enantioenriched schweinfurthin B analogs were undertaken to develop structure-activity relationships and guide design of probes for their putative molecular target. The desired stilbenes contain a common left-half hexahydroxanthene ring system and an aromatic right-half with varied substituents. The synthesis involves penultimate Horner-Wadsworth-Emmons coupling of one of several right-half phosphonates with the aldehyde comprising the left-half of 3-deoxyschweinfurthin B. Preparation of the requisite phosphonates, and the respective stilbenes, as well as the cytotoxicity profiles of these new compounds in the National Cancer Institute's 60 cell-line anticancer screen is described. Several of these analogs displayed cytotoxicity patterns well-correlated with the natural product and differences in activity of approximately 10(3) across the various cell lines. Together, these assay results indicate the importance of at least one free phenol group on the aromatic D-ring of this system for differential cytotoxicity.