Kiyoshi Bessho

Synthesis and evaluation of nitro 5-deazaflavins as novel bioreductive antitumor agents

Abstract A series of nitro 5-deazaflavins, 5-deazaflavins possessing a nitro group at C(6)–C(9) position, has been designed and synthesized as a novel class of bioreductive nitrohetero-aromatic compounds and their cytotoxicities towards L1210 and KB cells were evaluated. It has been found that the nitro 5-deazaflavins undergo one electron reduction on the nitro group and undergo two electrons or “(net) hydride” reduction on the C(5)-C(4a)-C(10a)-N(1) redox system. They showed much more potent antitumor activities than the other 5-deazaflavins bearing no nitro group. These results suggest that an activation of nitro group by biological one electron reduction is crucial for an expression of cytotoxicity.

Synthesis and evaluation of nitro 5-deazaflavin-pyrrolecarboxamide(s) hybrid molecules as novel DNA targeted bioreductive antitumor agents.

A series of 6-nitro-5-deazaflavins bearing at N(3) or N(10) position the pyrrolecarboxamide(s) group as DNA minor groove binder has been synthesized. These hybrid molecules show similar redox properties to those of 6-nitro-5-deazaflavins with no pyrrolecarboxamide(s) group, suggesting that they generate stable one- and two-electron reduction product(s). Electrolytic reductions of the hybrid molecules were carried out at a controlled potential under anaerobic conditions in the presence of plasmid pBR322 DNA. Significant conversions of the supercoiled circular pBR322 DNA (form I) to the open circular DNA (form II) have been found by treatment with the reductively activated 6-nitro-5-deazaflavin derivatives. Their DNA damaging effects have been found to be enhanced as the number of pyrrolecarboxamide group as the DNA binder increases. Antitumor activities of the hybrid molecules towards KB and L1210 cells were evaluated in vitro. It has been found that the antitumor effects of the compounds on KB cells slightly change and those on L1210 cells decrease as the number of the pyrrolecarboxamide group increases. These results reveal that the combination of 6-nitro-5-deazaflavin molecule with the pyrrolecarboxamide(s) group increase the DNA binding properties of the compounds, giving rise to promoted DNA damaging effects, and also suggest that the combination would affect the capacity of the compounds to act as the substrate for intracellular reductases and/or the cellular uptake of the compounds.

SYNTHESIS AND DNA BINDING PROPERTIES OF AMIDE BOND-MODIFIED ANALOGUES RELATED TO DISTAMYCIN

Abstract Novel nitro analogues of distamycin which have trans olefin or α-diketo moiety instead of amide bond were synthesized. Their DNA binding properties studied by ethidium displacement assay and MPE footprinting experiments were also described.

Evaluation of differential hypoxic cytotoxicity and electrochemical studies of nitro 5-deazaflavins

Abstract Cytotoxicities of nitro 5-deazaflavins were evaluated in vitro towards hypoxic and oxic Chinese hamster cells (V79). 6-Nitro and 8-nitro derivatives were generally more toxic towards hypoxic cells than oxic cells, showing marked hypoxic selectivity. In contrast, 7-nitro and 9-nitro derivatives showed no significant hypoxic selectivity. Electrochemical study using cyclic voltammetry (CV) revealed that 6-nitro and 8-nitro derivatives generate a stable two electrons reduction product as well as a stable one electron reduction product and that 7-nitro and 9-nitro derivatives afford an unstable one electron reduction product. These results strongly support that not solely electron affinity but also stability of the one electron reduction products is crucial for the differential hypoxic cytotoxicities of nitro 5-deazaflavins.

Remarkable difference in reactivity of ordinary vinylcopper reagents and vinylzinc halide containing a copper salt towards γ-mesyloxy-α, β-enoates. Synthesis of homochiral 1,4-dienes

Abstract Whereas the reaction of γ-mesyloxy α,β-enoates with vinyl-Cu(CN)M or (vinyl) 2 Cu(CN)M 2 (M = Li or MgX) yielded a reduction product with an ( E )-double bond at the β,γ-position, treatment of the same substrates with “higher order” zinc cuprate reagents or vinyl-ZnCl by the addition of a catalytic amount of Cu(I) or Cu(II) salt afforded α- and γ-vinylation products. Both vinylation products were stable 1,4-diene derivatives that are only more difficulty accessed by more traditional means.

Studies on Peptides CLVIII. Model Experiments for the Synthesis of Open-Chain Unsymmetrical Cystine-Peptides

Treatment of a mixture of Cys(R)(O) and Cys(R′) with an acid was found to generate cystine in fairly good yields, when suitable R, R′, and an acid were selected. An unsymmetrical cystine peptide was prepared by treatment of a mixture of Z(OMe)-Cys(R) (0)-Ala-NH2 (R=Acm or MBzl) and Z(OMe)-Cys(MBzl)-Gly-OBzl with TFA or 1 M TFMSA/TFA.3 Oxytocin was obtained in an excellent yield by TFA treatment of the protected peptide containing Cys(Acm)(0) and Cys(MBzl). Thus, formation of the disulfide bond was found feasible at the position of Cys(R) (0).

New procedure for the synthesis of cystine-peptides by oxidation of S-substituted cysteine-peptides with thallium(III) trifluoroacetate

Thallium(III) trifluroacetate cleaves various S-protecting groups of cysteine in trifluoroacetic acid forming cystine; as examples, three model peptides, oxytocin, urotensin II, and a human calcitonin gene-related peptide, were prepared by direct oxidative conversion of the respective S-substituted cysteine-peptides.

Synthesis of a new type of 5-deazaflavoquinone. (hybrid model compound of 5-deazaflavin and coenzyme PQQ)

Abstract A novel chemical hybrid model compound of 5-deazaflavin and PQQ was designed and synthesized via the suitably substituted 5-deazaflavin (5-deazaisoalloxazine) intermediate, followed by the oxidation to introduce orthoquinone group; the obtained model compound showed higher autorecycling oxidizing ability for benzylamine than usual 5-deazaflavins.

Stereochemistry of asymmetric “(net) hydride transfer” in an intercoenzyme model reaction system

Abstract X-ray crystal structure analysis revealed the absolute configuration of compound 2 and thus proved the absolute configuration of 5-deazaflavin (+)-1 possessing both axial and planar chirality to be (S). Model reactions of “(net) hydride transfer” between 1 and Me2PNPH enanatiomers revealed that (S)-(+)-1 oxidizes (4S)-Me2PNPH more rapidly than its (4R) isomer and that (R)-(−)-1 oxidizes (4R)-Me2PNPH more rapidly than its (4S) isomer. These results strongly suggest that an enatioselectivity on Me2PNPH by chiral 1 is not solely determined by the availability of C(4) hydrogen but by the “(net) hydride donor-acceptor” interactions involving the interaction between the pyrimidine site of 5-deazaflavin molecule and the carbamoyl group of the NAD(P)H model as the important contributor.

Variation of reaction channel in a flavoenzyme model with a modified pyrimidine ring

Abstract A chiral 5-deazaflavin derivative with 2-hydroxymethylphenyl group at N(3) position of the pyrimidine ring has been synthesized. Oxidized form of the 5-deazaflavin derivative is reduced stereo-specifically: the hydroxymethyl group exerts steric inhibition in the absence of Mg 2+ , whereas it facilitates the approach of a reducing agent in the presence of Mg 2+ .