Naturally occurring quinones as potential bioreductive alkylating agents

Nucleophilic activation of a tetra-substituted mitomycin cyclic bis-disulfide

The multimerization of functional DNA alkylating agents has drawn significant, recent interest because these compounds are expected to generate enhanced levels of DNA cross-linked adducts, compared with their monomeric agents. Here we report the evaluation of 7-N,7'-N'-(1'',2'',9'',10''-tetrathia-cyclohexadecanyl-3'',8'',11'',16''-tetramethylenyl)tetrakismitomycin C (8), in which four mitomycin units are attached to the novel bis-disulfide linker, 3,8,11,16-tetrakis(aminomethyl)-1,2,9,10-tetrathia-cyclohexadecane. Compound 8 was designed to undergo preferential C(1) mitomycin activation under nucleophilic as well as under acidic and reductive conditions. We anticipated that treating 8 with nucleophiles would lead to bis-disulfide cleavage thus producing two mitomycin dimers (9) capable of generating DNA interstrand cross-links (ISC). The mitomycin units in 9 are tethered by a stable carbon backbone linkage. According to the procedure reported by Lee and coworkers (Tetrahedron, 61, 1749-1754 (2005)), we synthesized 8 and the reference mitomycin dimer, 7-N,7'-N'-(2'',7''-dihydroxy-1'',8''-octanediyl)bismitomycin C (15). Compound 8 was activated under acidic conditions thereby generating mitosene product 16, in which all four mitomycin units within the 16-membered ring were activated. Using the nucleophile Et(3)P, we found that 8 underwent significantly enhanced mitosene production compared with its reference compound 15. We further demonstrated that under nucleophilic activation conditions 8 generated higher levels of DNA ISC than either 1 or 15. The cytotoxicities of 8 and 15 in a select tumor cell line were evaluated and compared with mitomycin C (1).

Structure and conformation of 1-beta-D-ribo furanosyl pyridin-2-one-5-carboxamide: an anti-inflammatory agent

The pyrimidine nucleoside, 1-beta-D-ribofuranosyl pyridine-2-one-5-carboxamide, is an anti inflammatory agent used in the treatment of adjuvant-induced arthritis. It is the 2-one isomer of 1-beta-D-ribofuranosyl pyridine-4-one 5-carboxamide, an unusual nucleoside isolated from the urine of patients with chronic myelogenic leukemia and an important cancer marker. Crystals of 1-beta-D-ribofuranosyl pyridine-2-one-5-carboxamide are monoclinic, space group C2, with the cell dimensions a = 31.7920(13), b = 4.6872 (3), c = 16.1838(11), beta = 93.071(3) degrees , V = 2408.2(2) A(3), D(calc) = 1.496 mg/m(3) and Z = 8 (two molecules in the asymmetric unit). The structure was obtained by the application of direct methods to diffractometric data and refined to a final R value of 0.050 for 1669 reflections with I >or= 3sigma. The nucleoside exhibits an anti conformation across the glycosidic bond (chi(CN) = -15.5 degrees , -18.9 degrees ), a C3 '-endo C2 '-exo [(3)(2)T] ribose pucker and g(+) across the C(4 ')-C(5 ') exocyclic bond. The amino group of the carboxamide group is distal from the 2-one and lacks the intramolecular hydrogen bonding found in the related 2-one molecule. Nuclear magnetic resonance studies shows also an anti conformation across the glycosidic bond but the solution conformation of the furanose ring is not the same as that found in the solid state.

Handling of biological samples in the determination of the anti-neoplastic drug mitomycin C

A study to ascertain suitable conditions for handling biological samples from patients, treated with the antibiotic mitomycin C (MMC), with the objective of improving the accuracy and reliability of the determination is described. Situations frequently occurring in medical practice are simulated to optimize procedures for reliable and reproducible sampling, sample treatment and determination of MMC. Continuation of drug partitioning in whole blood after sampling can be prevented by immediate cooling in ice before the separation of plasma from cells. The adjustment of the pH of urine samples is shown to be particularly important since a low urinary pH causes decomposition of MMC; moreover, it may decrease extraction recovery. Furthermore, long-term exposure of samples to daylight induces drug decomposition. Frozen storage of plasma and urine samples for periods greater than 3 weeks is to be avoided as this results in a considerable drop in MMC concentration. Repeated cycles of freezing and thawing are shown to have no effect upon the analytical results (6 cycles tested). The analysis of extracts of biological samples may take place up to at least 24 h after their preparation without measurable loss of analyte.

Synthesis and biological activities of quinazoline derivatives with ortho-phenol-quaternary ammonium salt groups

One phenol-quaternary ammonium salt derivative with a flexible linker and three derivatives with a quinazoline moiety are present. Their binding affinities for DNA are discussed and it is clearly demonstrated that this class of phenol-quaternary ammonium salt derivatives could inhibit DNA transcription effectively.

Selective N1-Alkylation of 2′-Deoxyguanosine with a Quinolinyl Quinone Methide

Nucleobase modification by quinone methides (QMs) has been extensively studied in the past decade, and multiple QM adducts were observed. For 2'-deoxyguanosine (dG), the N (2)-dG alkylation adduct was favored under aqueous buffered conditions over other N1-dG, N7-dG, and N7-guanine adducts. We report in this communication that the N1-dG adduct was selectively formed with a quinolinyl QM in 30% aqueous DMF and 10 mM phosphate buffer (pH 7.0) as a favored dG alkylation product. The quinolinyl QM was formed through the fluoride-induced desilylation and elimination of acetate, and the structure of the N1-dG adduct was fully established by one- and two-dimensional NMR analyses. In addition, the concentration of salt played a significant role in N1-dG adduct formation. Further HPLC analysis indicated that the addition of salt decreased the rate of QM formation from the acetate intermediate, although an in-depth mechanistic study is needed.

TESOTf-induced rearrangement of quinols. Efficient construction of the fully functionalized carbon skeleton of the griseusins by a divergent-reconvergent approach

[reaction: see text] The "reverse polarity" or "umpolung" strategy for the total synthesis of aryl C-glycosides was developed in the context of the antibiotic (-)-griseusin B. Although a key reaction in a model sequence for the total synthesis produced two structurally divergent products, both were converted to the same advanced model intermediate that contains the complete carbon skeleton and (except for the extraneous oxygen substituent in the model series) the functional group pattern of the griseusins.

Synthesis and antimicrobial activity of pyranobenzoquinones related to the pyranonaphthoquinone antibiotics

The synthesis and antimicrobial activity of isochromane-type analogs of the pyranonaphthoquinone antibiotics are reported. Isochromane derivatives with (17a, b) and without (22a, b) a C-4 hydroxyl moiety and their corresponding quinones (19a and 23), were prepared. Both quinones exhibited antimicrobial activity against Staphylococcus aureus, Bacillus atrophaeus and Streptococcus agalactiae, while the related isochromanes were inactive. The results suggest that the quinone moiety is important for biological activity while the C-4 hydroxyl may not be essential.

Design of a Cyclopropyl Quinone Methide Reductive Alkylating Agent. 2

A cyclopropyl quinone methide is formed by elimination of a leaving group from an appropriately functionalized hydroquinone. The presence of a carbon spacer results in the formation of a fused ring rather than the classic methide species. Discussed herein is cyclopropyl quinone methide formation from a pyrido[1,2-a]indole ring system. Both nucleophilic and electrophilic attack on the fused cyclopropane ring results in pyrido[1,2-a]indole and azepino[1,2-a]indole products. The stereoelectronic effect plays less a role in the relatively flexible pyrido[1,2-a]indole system compared to its role in the pyrrolo[1,2-a]-indole system. A 13C label on the fused cyclopropane ring permitted the rapid identification of complex rearrangement products observed in this study.

Phenol quaternary ammonium derivatives: charge and linker effect on their DNA photo-inducible cross-linking abilities

We report here that phenol derivatives with two and four quaternary ammoniums were synthesized and their abilities to bind and cross-link DNA were investigated. Thermal denaturizing studies indicated that derivatives possess similar DNA binding abilities and gel electrophoresis revealed that more charges (series B) and electronic donation substitute linkers (like -S-) dramatically increase the DNA cross-linking abilities.

Quinone Methide Formations in the Cu2+-Induced Oxidation of a Diterpenone Catechol and Concurrent Damage on DNA

Terpene quinone methides have been isolated from natural resources and exhibit broad biological activities against bacteria, fungi, and tumor cells through the reactive quinone methide (QM) moiety. The biological potential of the oxidation of terpene QM precursors, however, has not been assessed even though Cu(2+)-induced oxidation of catechol shows detrimental effects on cells. In this study, a diterpenone catechol was investigated as a precursor of terpene QM under aqueous conditions in the presence of Cu2+. Direct QM formation was implied in the Cu(2+)-induced oxidation through the study of thiol addition using HPLC and ESI-MS analysis. In addition, oxidation of the initial QM adduct to a second-QM intermediate was observed. The direct QM oxidation pathway may be unique for diterpenone catechol in the Cu(2+)-induced oxidation and is an addition to the reported isomerization pathway of o-quinones to QMs. The DNA damage by the Cu(2+)-induced oxidation of diterpenone catechol was assessed on a short duplex DNA target. Both direct DNA cleavage and nucleobase oxidation were observed extensively by in situ-generated hydroxyl radicals.

7-N,7'-N'-(1",2"-Dithianyl-3",6"-dimethylenyl)bismitomycin C: synthesis and nucleophilic activation of a dimeric mitomycin

Dimeric alkylating agents that modify complementary DNA strands have engendered significant interest. We have prepared the novel dimeric mitomycin, 7-N,7'-N'-(1",2"-dithianyl-3",6"-dimethylenyl)bismitomycin C (9), in which the mitomycins are bridged by a dithiane unit. Dimer 9, like the clinically tested acyclic disulfides KW-2149 (3) and BMS-181174 (4), was designed to activate under nucleophilic and reductive conditions. Successive nucleophile-mediated disulfide cleavage transformations of 9 are expected to generate thiol species ideally positioned to render the two mitomycin systems vulnerable to nucleophilic attack and permit DNA interstrand cross-link formation. The dithiane linker, strategically positioned between the two mitomycins, distinguished 9 from 3 and 4. Nucleophilic activation of this cyclic disulfide permitted both activated mitomycins to remain tethered to one another. We report the synthesis of 9, and show that the nucleophile Et(3)P markedly enhances the activation and consumption of 9, compared with the reference compound 7-N, 7"-N'-(cyclohexanyl-trans-1",4"-dimethylenyl)bismitomycin C (27). We further demonstrated that provides higher levels of DNA interstrand cross-links than either the dimeric reference compounds, and 7-N,7-N'-(2",5"-dihydroxy-1",6"-hexanediyl)bismitomycin C (28), or the monomeric mitomycins, 1 and 3, when Et(3)P is added to solutions containing EcoRI-linearized pBR322 DNA.

Design and synthesis of novel sugar-oxasteroid-quinone hybrids

A new class of sugar-oxasteroid-quinone hybrid molecules has been designed and synthesized involving an efficient enyne metathesis/Diels-Alder reaction strategy.

Cyclic Disulfide C(8) Iminoporfiromycin: Nucleophilic Activation of a Porfiromycin

The clinical success of mitomycin C (1) and its associated toxicities and resistance have led to efforts to prepare semisynthetic analogues (i.e., KW-2149 (3), BMS-181174 (4)) that have improved pharmacological profiles. In this study, we report the preparation and evaluation of the novel 7-N-(1'-amino-4',5'-dithian-2'-yl)porfiromycin C(8) cyclized imine (6) and its reference compound, 7-N-(1'-aminocyclohex-2'-yl)porfiromycin C(8) cyclized imine (13). Porfiromycin 6 contains a disulfide unit that, upon cleavage, may provide thiol(s) that affect drug reactivity. We demonstrated that phosphines dramatically accelerated 6 activation and solvolysis in methanolic solutions ("pH 7.4") compared with 13. Porfiromycins 6 and 13 efficiently cross-linked EcoRI-linearized pBR322 DNA upon addition of Et3P. We found enhanced levels of interstrand cross-link (ISC) adducts for 6 and 13 compared with porfiromycin (7) and that 6 was more efficient than 13. The large Et3P-mediated rate enhancements for the solvolysis of 6 compared with 13 and a N(7)-substituted analogue of 1, and the increased levels of ISC adducts for 6 compared with 13 and 7 are attributed to a nucleophile-assisted disulfide cleavage process that permits porfiromycin activation and nucleophile (MeOH, DNA) adduction. The in vitro antiproliferative activities of 6 and 13 using the A549 tumor cell line (lung adenocarcinoma) were determined under aerobic and hypoxic conditions and then compared with 7. Both 6 and 13 were more cytotoxic than 7, with 13 being more potent than 6. The C(8) iminoporfiromycins 6 and 13 displayed anticancer profiles similar to 3.

Reactions of the natural lignan hydroxymatairesinol in basic and acidic nucleophilic media: formation and reactivity of a quinone methide intermediate

The chemical properties and synthetic modifications of the natural lignan hydroxymatairesinol in basic and acidic nucleophilic media were studied. Hydroxymatairesinol presumably reacts via a quinone methide and a carbonium ion mechanism under basic and acidic conditions, respectively. In these conditions the benzylic hydroxyl group was displaced by nucleophiles yielding new 7-substituted butyrolactone lignans. Reactions in alcoholic basic solutions yielded the 7-alkoxy ethers diastereoselectively. Several previously known lignans as well as new lignans and lignan derivatives were synthesised. The transformations were monitored and the products identified by HPLC-MS and NMR.

l-Deprenyl as an inhibitor of menadione-induced permeability transition in liver mitochondria

L-Deprenyl, an inhibitor of mitochondrial monoamine oxidase B (MAO B), inhibits the swelling of liver mitochondria induced by the pro-oxidant 2-methyl-1,4-naphtoquinone with a K(i) dependent on quinone concentration. L-Deprenyl also inhibits the collapse of membrane potential, cation efflux, pyridine nucleotide oxidation and cytochrome c release, all events which accompany the osmotic change and are typical of membrane permeability transition induction, thus emphasizing the inhibitory effect of the drug on this phenomenon. Results show that this inhibition is not due to the effect of L-deprenyl on monoamine oxidase activity but is most likely due to a direct interaction of the drug with the pore forming structures. It is here proposed that L-deprenyl, being a propargylamine, at physiological pH has a protonated amino group able to interact with critical aromatic or anionic amino acidic residues. As a consequence, the opening of the transition pore is prevented. These results indicate a more generalized protective effect of L-deprenyl on mitochondrial functions, involving the inhibition of membrane permeability transition induced not only by the oxidation of substrates of MAO B, but also by pro-oxidant agents such as 2-methyl-1,4-naphtoquinone, which does not involve MAO B activity.

Use of a Sonogashira−Acetylide Coupling Strategy for the Synthesis of the Aromatic Spiroketal Skeleton of γ-Rubromycin

[reaction: see text] The synthesis of the fused aromatic spiroketal core of gamma-rubromycin is described via addition of an aryl acetylide fragment to an aryl acetaldehyde fragment. In turn, the aryl acetylene precursor was readily prepared with use of a Sonogashira reaction.

Suzuki-Miyaura homocoupling of naphthyl triflates using bis(pinacolato)diboron: approaches to the biaryl skeleton of crisamicin A

Homocoupling of naphthyl triflates 27, 16, 17 to the respective binaphthyls 28, 31 and 35 has been achieved in a one-pot procedure using bis(pinacolato)diboron and PdCl2(dppf). Use of potassium acetate as the base provides access to the initial naphthylboronate intermediates whereas the stronger base potassium phosphate is required in order to promote subsequent coupling of the naphthylboronate with a second equivalent of the naphthyl triflate. Attempts to convert binaphthyl 35 into bis-acetylnaphthalene 14, a key intermediate for the synthesis of the dimeric pyranonaphthoquinone antibiotic crisamicin A 2, via double Fries rearrangement of bis-acetate 37 derived from binaphthyl 35, were unsuccessful. Attempts to introduce the acetyl groups at C-7 and C-7' on bis-acetylnaphthalene 14 via Fries rearrangement of the monomeric precursors 21 and 15, before effecting homocoupling to a biaryl were unsuccessful. Introduction of an acetyl group via initial bromination ortho to the hydroxyl group in naphthol 18, which bears an electron rich benzyl ether at C-7, was plagued by the formation of phenolic coupling product 42 and naphthoquinone 43. Bromination of naphthol 45, bearing a less electron rich triflate group at C-7, also afforded binaphthol 47 resulting from phenolic coupling as well as naphthoquinone 48 when using N-bromosuccinimide at low temperature.

A potent, water-soluble and photoinducible DNA cross-linking agent

Water-soluble DNA cross-linking phenol and biphenol derivatives 3 and 6 have been synthesized by a Mannich reaction. Both of them can cross-link DNA by photoactivation using visible light (wavelength > 400 nm). Compound 6 can cross-link DNA at pH 5.0 and 7.7, whereas no cross-link was observed at pH 10.0. Density functional theory (DFT) calculation indicated that 6 displays a twist structure. Therefore, it could bind to DNA naturally and has potent property to cross-link DNA after photoactivation.

7-N-(mercaptoalkyl)mitomycins: implications of cyclization for drug function

The Kyowa Hakko Kogyo and Bristol-Myers Squibb companies reported that select mitomycin C(7) aminoethylene disulfides displayed improved pharmacological profiles compared with mitomycin C (1). Mechanisms have been advanced for these mitomycins that differ from 1. Central to many of these hypotheses is the intermediate generation of 7-N-(2-mercaptoethyl)mitomycin C (5). Thiol 5 has been neither isolated nor characterized. Two efficient methods were developed for mitomycin (porfiromycin) C(7)-substituted thiols. In the first method, the thiol was produced by a thiol-mediated disulfide exchange process using an activated mixed mitomycin disulfide. In the second route, the thiol was generated by base-mediated cleavage of a porfiromycin C(7)-substituted thiol ester. We selected four thiols, 7-N-(2-mercaptoethyl)mitomycin C (5), 7-N-(2-mercaptoethyl)porfiromycin (12), 7-N-(2-mercapto-2-methylpropyl)mitomycin C (13), and 7-N-(3-mercaptopropyl)porfiromycin (14), for study. Thiols 5 and 12-14 differed in the composition of the alkyl linker that bridged the thiol with the mitomycin (porfiromycin) C(7) amino substituent. Thiol generation was documented by HPLC and spectroscopic studies and by thiol-trapping experiments. The linker affected the structure of the thiol species and the stability of the thiol. We observed that thiols 5 and 12 existed largely as their cyclic isomers. Evidence is presented that cyclization predominantly occurred at the mitomycin C(7) position. Correspondingly, alkyl linker substitution (13) or extension of the linker to three carbons (14) led to enhanced thiol stability and the predominant formation of the free thiol species. The dominant reaction of thiols 5 and 12-14 or their isomers was dimerization, and we found no evidence that thiol formation led to mitosene production and aziridine ring-opening. These findings indicated that thiol generation was not sufficient for mitomycin ring activation. The potential pharmacological advantages of mitomycin C(7) aminoethylene disulfides compared with 1 is discussed in light of the observed thiol cyclization pathway.

Highly E-selective and effective synthesis of antiarthritic drug candidate S-2474 using quinone methide derivatives

We have developed an efficient and E-selective synthesis of an antiarthritic drug candidate (E)-(5)-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2-ethyl-1,2-isothiazolidine-1,1-dioxide (S-2474; 1), in which alpha-methoxy-p-quinone methide is used as a key intermediate. alpha-Methoxy-p-quinone methide was revealed to be an equivalent to a p-hydroxy protected benzaldehyde. It reacts smoothly with alpha-sulfonyl carbanion to give 1,6-addition intermediates, which can be further processed to provide S-2474 directly in the presence of a base. This procedure gives S-2474 as an almost single isomer on the benzylidene double bond in excellent yield and thus is a very practical method adaptable to large-scale synthesis. The detailed mechanistic aspects are studied and discussed.

Synthesis, DNA cross-linking activity, and cytotoxicity of dimeric mitomycins

Dimeric DNA cross-linking compounds have emerged as important new antitumor agents. We report the synthesis and biochemical evaluation of a select set of dimeric mitomycins in which the two mitomycin units are tethered at either the mitomycin C(7) amino or the aziridine N(1a) positions. Significantly, mitomycin C (1) itself is the prototypical bioreductive DNA cross-linking agent. DNA cross-linking experiments using a denaturing-gel-electrophoresis-based assay showed that the extent of DNA cross-linking for select dimeric mitomycins can exceed that of the parent compound, mitomycin C, and that the reaction proceeds, in part, at the two distal C(1) sites in the mitomycins. The efficiency of DNA cross-linking depended on the nature of the linker and the position of linker unit's attachment. When we compared the efficiency of DNA cross-linking for the dimeric mitomycins with their in vitro cytotoxicities in cultured human tumor cells, we observed a poor correlation. The mitomycins that gave the highest levels of DNA cross-linked adducts displayed the weakest cytotoxicities. These findings determined that the denaturing-gel-electrophoresis-based assay was a poor predictor of cytotoxic activity.

The effect of C(5) cytosine methylation at CpG sequences on mitomycin-DNA bonding profiles

Recent studies have documented that cytosine C(5) methylation of CpG sequences enhances mitomycin C (1) adduction. The reports differ on the extent and uniformity of 1 modification at the nucleotide level. We have determined the bonding profiles for mitomycin monoalkylation in two DNA restriction fragments where the CpG sequences were methylated. Three mitomycin substrates were used and two different enzymatic assays employed to monitor the extent of drug modification at the individual base sites. Drug DNA modification was accomplished with I and 10-decarbamoylmitomycin C (2) under reductive (Na2S2O4) condilions and with N-methyl-7-methoxyaziridinomitosene (3) under nonreductive conditions. The UvrABC incision assay permitted us to quantitate the sites of drug adduction, and the lambda-exonuclease stop assay provided a qualitative estimation of drug-DNA modification consistent with the UvrABC data. We learned that C(5) cytosine methylation (m5C) enhanced the extent of overall DNA modification. Using the UvrABC endonuclease assay, we found that modification by 1 increased 2.0 and 7.4 times for the two DNA restriction fragments. Analysis of the modification sites at the nucleotide sequence level revealed that guanine (G) was the only base modified and that the overall increased level of DNA adduction was due to enhanced modification of select m5CpG* (G* = mitomycin (mitosene) adduction sites) loci compared with CpG* sites: the largest differences reached two orders of magnitude. Significantly, not all CpG* sites underwent increased drug adduction upon C(5) cytosine methylation. The effect of C(5) cytosine methylation on the drug adduction profiles was less pronounced for G* sites located within dinucleotide sequences other than CpG*. We observed that DNA methylation often led to slightly diminished adduction levels at these sites. The different m5CpG* adduction patterns provided distinctive sequence-selective bonding profiles for 1-3. We have attributed the large differences in guanine reactivity to DNA structural factors created, in part, by C(5) cytosine methylation. The significance of these findings in cancer chemotherapy is briefly discussed.

Spectroscopic studies on iron complexes of different anthracyclines in aprotic solvent systems

Iron complexes of daunorubicin, idarubicin, pirarubicin, and doxorubicin in anhydrous DMF were studied by UV/vis, CD, fluorescence, Mössbauer, and EPR spectroscopy. Titration studies of the metal-free anthracyclines showed one (UV-detectable) deprotonation step requiring 2 equiv of base, compared to 1 equiv for quinizarine. Metal complexation was studied at three different metal/ligand ratios, and with increasing amounts of base. The results obtained from optical spectroscopy show the existence of two different complex species and give clear indications for the requirements of metal complexation. Complex species I, formed at a low iron-to-ligand ratio, is less dependent on base addition than complex species II formed with equimolar ferric ion. EPR and Mössbauer experiments provide further insight into the structures of both complex species. Lack of spin density of the Mössbauer samples in EPR indicates spin coupling between the metal centers. Mössbauer spectra consist of single quadrupole doublets with values typical for high-spin ferric ion in an octahedral arrangement. The Mössbauer spectroscopic features at 7 T exclude the presence of S = 0 dimers. Complex I represents a monomeric ferric iron complex whereas complex II is consistent with a more or less aggregrated oligomeric Fe-anthracycline system.

Inhibition of DNA cross-linking by mitomycin C by peroxidase-mediated oxidation of mitomycin C hydroquinone

Mitomycin C requires reductive activation to cross-link DNA and express anticancer activity. Reduction of mitomycin C (40 microm) by sodium borohydride (200 microm) in 20 mm Tris-HCl, 1 mm EDTA at 37 degrees C, pH 7.4, gives a 50-60% yield of the reactive intermediate mitomycin C hydroquinone. The hydroquinone decays with first order kinetics or pseudo first order kinetics with a t(12) of approximately 15 s under these conditions. The cross-linking of T7 DNA in this system followed matching kinetics, with the conversion of mitomycin C hydroquinone to leuco-aziridinomitosene appearing to be the rate-determining step. Several peroxidases were found to oxidize mitomycin C hydroquinone to mitomycin C and to block DNA cross-linking to various degrees. Concentrations of the various peroxidases that largely blocked DNA cross-linking, regenerated 10-70% mitomycin C from the reduced material. Thus, significant quantities of products other than mitomycin C were produced by the peroxidase-mediated oxidation of mitomycin C hydroquinone or products derived therefrom. Variations in the sensitivity of cells to mitomycin C have been attributed to differing levels of activating enzymes, export pumps, and DNA repair. Mitomycin C hydroquinone-oxidizing enzymes give rise to a new mechanism by which oxic/hypoxic toxicity differentials and resistance can occur.

Synthesis and in vitro antitumor activity of 2-alkyl, 2-aryl, and 2-piperazinyl benzimidazole-4,7-dione derivatives

A series of 2-alkyl, 2-aryl, and 2-piperazinyl benzimidazole-4,7-dione derivatives (7a-h) and 16m-o) were prepared, and their cytotoxicities were tested against three cancer cell lines (mouse lymphocytic leukemia cell line P388, and human gastric carcinoma cell lines SNU-1 and SNU-16). These compounds showed potent cytotoxicity against all of three cell lines tested, and especially SNU-16 was sensitive to them. 2-Aryl (7g,h) and 2-piperazinyl benzimidazole-4,7-dione derivative (16 m) were more potent than mitomycin C against P388 and SNU-16. Among benzimidazole-4,7-dione derivatives with alkyl group at position 2, 7a had the most potent cytotoxicity against all of the cell lines tested.

Iminium ion chemistry of mitosene DNA alkylating agents. Enriched 13C NMR and isolation studies

Described herein is a study of the reductive alkylation chemistry of mitosene antitumor agents. We employed a 13C-enriched electrophilic center to probe the fate of the iminium ion resulting from reductive activation. The 13C-labeled center permitted the identification of complex products resulting from alkylation reactions. In the case of DNA reductive alkylation, the type and number of alkylation sites were readily assessed by 13C NMR. Although there has been much excellent work done in the area of mitosene chemistry and biochemistry, the present study provides a number of new findings: (1) The major fate of the iminium ion is head-to-tail polymerization, even in dilute solutions. (2) Dithionite reductive activation results in the formation of mitosene sulfite esters as well as the previously observed sulfonate adducts. (3) The mitosene iminium ion alkylates the adenosine 6-amino group as well as the guanosine 2-amino group. The identification of the latter adduct was greatly facilitated by the 13C-label at the electrophilic center. (4) The mitosene iminium ion alkylates DNA at both nitrogen and oxygen centers without any apparent base selectivity. The complexity of mitosene reductive alkylation of DNA will require continued adduct isolation studies.

Inhibitors of topoisomerase II based on the benzodiimidazole and dipyrroloimidazobenzimidazole ring systems: controlling DT-diaphorase reductive inactivation with steric bulk

Described herein are the synthesis, cytotoxic properties, and topoisomerase II inhibition assays of benzodiimidazole and dipyrroloimidazobenzimidazole structural variants of the pyrrolo[1, 2-a]benzimidazole or APBI ring system. These ring variants were designed to inhibit topoisomerase II, much as the APBIs are able to do. Since only the quinone form of the APBIs can intercalate DNA, two-electron reduction to the hydroquinone by DT-diaphorase is known to deactivate these compounds. Indeed, the APBIs possess a high inverse correlation with the cellular concentration of DT-diaphorase. Therefore one feature of the ABPI structural variants is the excessive bulk about the quinone ring, which was predicted to diminish DT-diaphorase substrate activity. Another feature is the presence of one or two alkylating centers, which would permit alkylation of DNA and/or topoisomerase II. Inhibition assays for topoisomerase II-mediated relaxation of supercoiled DNA indicate that the benzodiimidazole and dipyrroloimidazobenzimidazole quinone ring systems are catalytic inhibitors of topoisomerase II. Both quinone systems exhibit cytotoxicity perhaps due to the lack of inactivation by DT-diaphorase as well as topoisomerase II inhibition. One quinone displayed the novel feature of cytotoxicity selectively against melanoma cell lines. In conclusion, the benzodiimidazole and dipyrroloimidazobenzimidazole quinone ring systems will be subjected to future analogue development and structure-activity studies.

Phosphodiester Alkylation with a Quinone Methide

Despite the wide array of studies involving DNA alkylation and cleavage with quinone methide generating compounds, there have been no reports on the alkylation of phosphodiesters with quinone methides. We have investigated the reaction of dialkyl phosphates with a p-quinone methide in order to determine the potential for alkylation to produce trialkyphosphates. These studies have revealed that a phosphodiester can be alkylated with a p-quinone methide when promoted by a Brønsted acid. The role of the Brønsted acid is to sufficiently activate the p-quinone methide to allow phosphodiester addition to occur. The alkyl substituents of the phosphodiester have been found to effect the reactivity of the dialkyl phosphate under the reaction conditions examined. Equilibrium conversions up to 83% trialkyl phosphate formation have been achieved.

Chemistry of puupehenone: 1,6-conjugate addition to its quinone-methide system

The marine natural product puupehenone (1), isolated in good yields from sponges of the genus Hyrtios, has been shown to undergo stereospecific 1,6-conjugate addition to its quinone-methide system. Several nucleophilic agents such as hydrogen cyanide, Grignard reagents, and nitroalkanes were studied, producing structurally diverse compounds. This lead optimization study was initiated due to the bioactivity of puupehenone and its natural analogues, which includes numerous previous reports of potential anticancer and antiinfective activity.