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. 2021 Jan 20;143(2):1126-1132.
doi: 10.1021/jacs.0c11960. Epub 2021 Jan 7.

Synthesis and Biological Evaluation of (2 S,2' S)-Lomaiviticin A

Miho Kaneko  1 , Zhenwu Li  1 , Matthew Burk  1 , Laureen Colis  1 , Seth B Herzon  1   2
Affiliations

Synthesis and Biological Evaluation of (2 S,2' S)-Lomaiviticin A

Miho Kaneko et al. J Am Chem Soc. .

Abstract

(-)-Lomaiviticin A (1) is a genotoxic C2-symmetric metabolite that arises from the formal dimerization of two bis(glycosylated) diazotetrahydrobenzo[b]fluorenes. Here we present a synthesis of the monomer 17 and its coupling to form (2S,2'S)-lomaiviticin A (4), an unnatural diastereomer of 1. (2S,2'S)-Lomaiviticin A (4) is significantly less genotoxic, a result we attribute to changes in the orientation of the diazofluorene and carbohydrate residues, relative to 1. These data bring the importance of the configuration of the conjoining bond to light and place the total synthesis of 1 itself within reach.

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Figures

Figure 1.
Figure 1.
a. Structures of (–)-lomaiviticin A (1), (–)-lomaiviticin C (2), (–)-lomaiviticin aglycon (3), and (2S,2’S)-lomaiviticin A (4). b. View of (–)-lomaiviticin A (1; pale blue) bound to d(GCTATAGC)2. The diazo nitrogen and carbon atoms are shown in royal blue and magenta, respectively. The light and dark red spheres correspond to A6H4′ and A14H1′ which are the aliphatic DNA hydrogen atoms closest to each diazo carbon (4.2 Å).
Figure 2.
Figure 2.
a. Dimerization of the enoxysilane 20 using manganese tris(hexafluoroacetylacetonate) provides the (2R,2’R)-coupling product selectively. The selectivity was attributed to contact ion pairing with the reduced oxidant, as in 21. b. The silyl ether product 22 was formed with 1:1–3:2 selectivity relative to the (2S,2’R) coupling product, suggesting the stereoselectivity in the dimerization of 17 does not derive from simple non-bonded interactions. c. The stereochemical outcome in the oxidative coupling of 23 (to form 18, Scheme 3) is attributed to neighboring group participation by the oleandrose residue, which shields the si face of the monomer and (potentially) promotes the final oxidation step following addition of the radical cation to the re face of the remaining enoxysilane.
Figure 3.
Figure 3.
a. Cytotoxicity of (–)-lomaiviticin A (1) and (2S,2’S)-lomaiviticin A (4) against the K562 leukemia cell line. Increasing concentrations of (–)-lomaiviticin A (1; 0⟶5 nM) reduced cell viability by >80% while (2S,2’S)-lomaiviticin A (4) was non-toxic at 5 nM concentration. Cell viability was determined using the CellTiter-Glo assay. b. Plasmid DNA cleavage assay employing (–)-lomaiviticin A (1) or (2S,2’S)-lomaiviticin A (4). (–)-Lomaiviticin A (1) extensively damaged DNA at 500 nM concentration while (2S,2’S)-lomaiviticin A (4) did not generate detectable levels of DNA damage at up to 1 mM concentration in the presence or absence of DTT. c. Immunofluorescence imaging of the DNA DSB repair factors γH2AX and 53BP1 in K562 cells treated with (–)-lomaiviticin A (1) or (2S,2[isp]’S)-lomaiviticin A (4). (–)-Treatment with 0.5 nM (–)-lomaiviticin A (1) led to activation of the DNA DSB response while (2S,2’S)-lomaiviticin A (4) did not activate the DNA DSB damage response at 50 nM concentration. Immunological detection was performed using a primary antibody (rabbit polyclonal anti-53BP1 antibody and mouse monoclonal anti-phospho-histone H2AX (SER139) antibody and visualized with Alexa 488 (goat-anti-mouse IgG) and Alexa 594 (goat-anti-rabbit IgG)). Mounting medium contained 4’,6-diamidino-2-phenylindole (DAPI) to visualize nuclear DNA. Full imaging data are shown in Fig. S1
Figure 4.
Figure 4.
Optimized (wB97X-D/6–311G*) structures of (–)-lomaiviticin A (1) and (2S,2’S)-lomaiviticin A (4). a. Front view. b. Side view. The naphthoquinone and cyclopentadiene rings are shown in yellow. The N-methyl substituents of the aminosugar are shown in magenta. Hydrogen atoms are omitted for clarity.
Scheme 1.
Scheme 1.
Synthesis of the bis(glycoside) 12.
Scheme 2.
Scheme 2.
Synthesis of the monomeric bis(glycosylated) diazofluorene 17.
Scheme 3.
Scheme 3.
Conversion of the monomeric bis(glycosylated) diazofluorene 17 to (2S,2’S)-lomaiviticin A (4).
See this image and copyright information in PMC

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