SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
As a first example of opening a secondary aziridine with a tertiary carbanion, the title amines (3a-c, aryl = phenyl, 4-tert-butylphenyl,2-naphthyl) were synthesized by opening N-(diphenylphosphinoyl)-7-azabicyclo[4.1.0]heptane, aziridine 1, with the corresponding alpha-potassium isopropylarenes, followed by a hydrolysis of the resulting phosphinamides 2a-c.
[formula: see text] trans-Aziridine-2-carboxylic acid derivatives are useful intermediates for the synthesis of threonine or allo-threonine through ring expansion and SN2 displacement, respectively. We describe here the preparation of the Ile-allo-Thr-Gly 11 fragment of Lysobactin via the aziridine 9 intermediate.
Two different chiral lithium amide base routes for the synthesis of amino- and aziridino-containing cyclohexenols have been explored. The first strategy involved the diastereoselective preparation of novel meso-aziridinocyclohexene oxides and their subsequent enantioselective rearrangement using chiral bases. In this approach, the diphenylphosphinoyl nitrogen protecting group proved optimal and aziridinocyclohexenols of 47-68% ee were obtained. Of particular note was the smooth rearrangement of the epoxide to an allylic alcohol in the presence of an aziridine: under optimised chiral base conditions, the aziridine remained essentially unaffected. A second more straightforward strategy for introduction of an amino functionality was also investigated: (1S,4R,5S)- and (1R,4R,5S)-4,5-bis(tert-butyldimethylsilyloxy)cyclohex-2-enols, readily prepared in > 95% ee using a chiral base approach, were subjected to Mitsunobu substitution using a sulfonamide and Overman rearrangement.
Alkyl aziridine analogues of the hypoxic cell radiosensitizer RSU 1069 have been synthesized and one of these, RB 7040, containing the tetramethyl substituted aziridine, is a more efficient sensitizer in vitro than RSU 1069 (Ahmed et al., 1986). The extent to which variation in drug uptake can influence the sensitizing efficiency of RSU 1069 and its analogues has been investigated by determining the cellular uptake of these weakly basic sensitizers as a function of the pH of the extracellular medium (pHe) over the range 5.4-8.4. Following exposure of V79 cells to these agents for 1 h at room temperature, the ratio of intra- to extracellular concentration (Ci/Ce) was near unity at pH 5.4. Increasing pHe to 8.4 resulted in no change in the ratio Ci/Ce for RSU 1069 (pKa = 6.04). In contrast, the values of Ci/Ce increased three-fold for RSU 1165 (pKa = 7.38) and eleven-fold for RB 7040 (pKa = 8.45). Radiosensitization by RSU 1069 showed little dependence on pHe over the range studied, whereas increasing pH caused an apparent increase in sensitizing efficiency of both RSU 1165 and RB 7040. However, when the enhancement ratios for sensitization were normalized to take account of the effect of extracellular pH on drug uptake, efficiency of sensitization was independent of pHe. This study suggests that changes in basicity (pKa) may have wider potential for therapeutic exploitation on the basis of selective tumour uptake for this type of agent.
The presence of an aziridine ring in mitomycin C suggests that the mechanism of action of the antibiotic is like that of the antitumor alkylating agents. However the compound is unexpectedly stable during aerobic incubation with rat liver homogenates although rapidly metabolized anaerobically. Mitomycin is not reactive with gamma-(4-nitrobenzyl) pyridine and reacts only slowly at acid p(H) with thiosulfate. It is proposed that mitomycin is activated in vivo, possibly by a reduction which "unmasks" the potential activity of the fused aziridine ring.
The cytotoxic action of the antitumor antibiotic mitomycin C occurs primarily at the level of DNA. Using highly sensitive fluorescence assays which depend on the enhancement of ethidium fluorescence only when it intercalates duplex regions of DNA, three aspects of mitomycin C action on DNA have been studied: (a) cross-linking events, (b) alkylation without necessarily cross-linking, and (c) strand breakage. Cross-linking of DNA is determined by the return of fluorescence after a heat denaturation step at alkaline pH's. Under these conditions denatured DNA gives no fluorescence. The cross-linking was independently confirmed by S1-endonuclease (EC 3.1.4.-) digestion. At relatively high concentrations of mitomycin the suppression of ethidium fluorescence enhancement was shown not to be due to depurination but rather to alkylation, as a result of losses in potential intercalation sites. A linear relationship exists between binding ratio for mitomycin and loss of fluorescence. The proportional decrease in fluorescence with pH strongly suggests that the alkylation is due to the aziridine moiety of the antibiotic under these conditions. A parallel increase in the rate and overall efficiency of covalent cross-linking of DNA with lower pH suggests that the cross-linking event, to which the primary cytotoxic action has been linked, occurs sequentially with alkylation by aziridine and then by carbamate. Mitomycin C, reduced chemically, was shown to induce single strand cleavage as well as monoaklylation and covalent cross-linking in PM2 covalently closed circular DNA. The inhibition of this cleavage by superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6), and by free radical scavengers suggests that the degradation of DNA observed to accompany the cytotoxic action of mitomycin C is largely due to the free radical O2. In contrast to the behavior of the antibiotic streptonigrin, mitomycin C does not inactivate the protective enzymes superoxide dismutase or catalase. Lastly, mitomycin C is able to cross-link DNA in the absence of reduction at pH 4. This is consistent with the postulated cross-linking mechansims.
Angiotensin-converting enzyme 2 (ACE2) is considered an important therapeutic target for controlling cardiovascular diseases and severe acute respiratory syndrome (SARS) outbreaks. Recently solved high-resolution crystal structures of the apo-bound and inhibitor-bound forms of ACE2 have provided the basis for a novel molecular docking approach in an attempt to identify ACE2 inhibitors and compounds that block SARS coronavirus spike protein-mediated cell fusion. In this study, approximately 140 000 small molecules were screened by in silico molecular docking. In this structure-activity relation study, the molecules with the highest predicted binding scores were identified and assayed for ACE2 enzymatic inhibitory activity and for their ability to inhibit SARS coronavirus spike protein-mediated cell fusion. This approach identified N-(2-aminoethyl)-1 aziridine-ethanamine as a novel ACE2 inhibitor that also is effective in blocking the SARS coronavirus spike protein-mediated cell fusion. Thus, the molecular docking approach resulting in the inhibitory capacity of N-(2-aminoethyl)-1 aziridine-ethanamine provides an attractive small molecule lead compound on which the development of more effective therapeutic agents could be developed to modulate hypertension and for controlling SARS infections.
We have used chemical cross-linking and dense amino acid labeling of estrogen receptors to characterize the subunit nature and rate of turnover of nuclear 5S estrogen-receptor complexes. When MCF-7 human breast cancer cells are incubated with [3H]estradiol or [3H]antiestrogen [alpha-[4-pyrrolidinoethoxy]phenyl-4-hydroxy-alpha'-nitrostilbe ne (CI628M) or (Z)-1-[4-(2-[N-aziridinyl]ethoxy)phenyl] 1,2-diphenyl-1-butene (tamoxifen aziridine)] and nuclear estrogen-receptor complexes are extracted with 0.6 M KCl and then chemically cross-linked with the cross-linker 2-iminothiolane, the cross-linked receptor complexes sediment as a 5.4S species on 3 M urea-containing sucrose gradients, while the noncross-linked species are 4S. Sodium dodecyl sulfate-polyacrylamide gel analyses of these cross-linked nuclear receptor complexes labeled with the covalently attaching ligand [3H]tamoxifen aziridine reveal a species of about 130,000 mol wt, while the noncross-linked or the cross-linked but mercaptan-cleaved receptor is 65,000 mol wt. Both receptor species are also detectable by interaction with an immunoadsorbent column containing antireceptor monoclonal antibody. For analyses of receptor turnover rates, cells exposed for different time periods to medium containing dense (15N, 13C, and 2H) amino acids were labeled with [3H]antiestrogen [1-[4-(2-dimethylaminoethoxy)phenyl]1-[4-hydroxyphenyl] 2-phenylbut-1-(2)ene (trans-hydroxytamoxifen) or CI628M] or [3H]estradiol, and salt-extracted nuclear estrogen receptors were analyzed on sucrose gradients. The normal density 5S form shifted to a broader, more dense peak at 2 and 4 h and finally, by 8-10 h, to a more dense, sharply sedimenting species. The time course of this shift is the same as that seen for the 4S urea-dissociated nuclear receptor form (t1/2 approximately 4h), suggesting that the 5.4S nuclear receptor is composed of two species which turn over at the same rate. We conclude from these cross-linking and density shift experiments that the nuclear 5S receptor complex consists of two similarly sized units, which turn over with similar half-lives. These data provide strong evidence that the 5S nuclear receptor complex is a homodimer of two 4S, 65,000 mol wt monomers.
Mucohalogen acids have been used for the preparation of a variety of 3,4-dihalogenated 2(5H)-furanones. In one synthetic step the carbamates 2a-c and the pseudoanhydrides 4a-e were prepared using isocyanates and acid anhydrides. A series of 5-alkoxylated 3,4-dichloro-2(5H)-furanones 5a-o have been synthesized with a wide range of lipophilicity, using the hydroxy-form of mucohalogen acids 1a and 1b. The 5-allyl-3,4-dichloro-2(5H)-furanone 5f was derived into the dihydro-isoxazol 6 and the oxirane 7. The methyl ester 5a was converted with ammonia into the tetramic acid chloride 11. The pseudo acid chloride 3 was reacted further into the bis aziridine 8. Reduction of the mucochloric acid 1a furnished the trichlorofuranone 3. The cytotoxicity of these simple and bis-cyclic butenolides have been evaluated in tissue culture on MAC13 and MAC16 cancer cell lines using the MTT cytotoxicity assay. The ester 5g, the acetate 4b and the carbamate 2b displayed a cytotoxicity in the low micromolar range. Further, an IC50 (50% inhibitory concentration) of 50 nM and 30 nM was determined for the epoxide 7 and the aziridine 8.
The metabolism of quinone-containing antitumor agents involves enzymatic reduction of the quinone by one or two electrons. This reduction results in the formation of the semiquinone or the hydroquinone of the anticancer drug. The consequence of these enzymatic reductions is that the semiquinone yields its extra electron to oxygen with the formation of superoxide radical anion and the original quinone. This reduction by a reductase followed by oxidation by molecular oxygen (dioxygen) is known as redox-cycling and continues until the system becomes anaerobic. In the case of a two electron reduction, the hydroquinone could become stable, and as such, excreted by the organism in a detoxification pathway. In some cases such as aziridine quinones, the hydroquinone can be oxidized by one electron at a time resulting in the production of superoxide, the semiquinone and the parental quinone. Quinone anticancer agents upon reduction can also set up an equilibrium between the hydroquinone, the parental quinone and the semiquinone which results in a long-lived semiquinone. Depending on the compound, aziridine quinones, for example, this equilibrium is long lasting thus allowing for the detection of the semiquinone under aerobic conditions. This phenomenon is known as comproportionation-disporportionation equilibrium. The series of reviews in this Special Issue address the consequences of bioreduction of quinone alkylators used in the treatment of cancer. In this particular review we are interested in describing the phenomenon of redox-cycling, how it is measured, and the biological consequences of the presence of the semiquinone and the oxygen radicals generated.
In order to analyse the molecular weight polymorphism of the estrogen receptor (ER) in MCF-7 cells, we have developed a procedure which allowed in situ linkage of ER by (3H) tamoxifen aziridine and provided labelled proteins in conditions which minimized protease activities. After labelling, cell lysis was performed in SDS buffer containing various concentrations of [symbol: see text]-mercaptoethanol. Proteins extracted with phenolic solution and precipitated by cold acetone were analysed by SDS PAGE. It appears that beside the form of 67 kDa already described, binding entities of tamoxifen aziridine were also present at a molecular mass of 110 kDa and 45 kDa. On the other hand, investigations on the effect of 12-0-Tetradecanoyl Phorbol 13-Acetate (TPA) showed that TPA induces a decrease of the 67 kDa entity.
A structural characteristic of many antiestrogens (AEs) is a bulky side chain with basic or polar functional groups that may interact with charged and polar amino acids near the hormone-binding site in the estrogen receptor. Recently, we have identified Cys530 as the residue of the human estrogen receptor that is the site of covalent labeling by aziridine analogs of estrogens (Es) and AEs (Harlow, K. W., Smith, D. N., Katzenellenbogen, J. A., Greene, G. L., and Katzenellenbogen, B. S. (1989) J. Biol. Chem. 264, 17476-17485). Since the aziridine function is on the bulky side chain of these ligands, Cys530 must be at or near the site of those side chain interactions. To probe these interactions, we have, by site-directed mutagenesis, made mutant human estrogen receptors in which charged and polar amino acids near Cys530 are changed (Glu523 to Gln, Lys529 and Lys531 to Gln, Asn532 to Asp, and Asp538 to Asn) so as to alter charge with minimal steric alteration. These receptors were expressed in mammalian (Chinese hamster ovary or COS-1) cells and assayed for their binding affinity for Es and AEs, their interaction with estrogen-responsive element DNA, and their ability to activate or suppress transcription of estrogen-responsive reporter genes. Two of the estrogen receptor mutants, KKN-QQD (mutation of Lys529, Lys531, and Asn532 to Gln529, Gln531, and Asp532, respectively) and KK-QQ (mutation of Lys529 and Lys531 to Gln529 and Gln531, respectively), in which the local charge is changed from +2 to -1 or 0, respectively, display an affinity for estradiol (E2) 5-10 times lower than that of the wild-type receptor, which is attributable to an enhanced rate of E2 dissociation. Although these mutant receptors have reduced affinity for a variety of Es, they retain unaltered affinity for AE. The profiles of transcriptional activation of reporter genes by various concentrations of E2 show that these two mutants (KKN-QQD and KK-QQ) require 40- and 15-fold higher E2 concentrations, respectively, to achieve half-maximal activity. In contrast, mutants E523Q and D538N, with changes at amino acids further from Cys530, were unaltered in their hormone binding and transactivation activity by E or AE. Interestingly, the AEs 4-hydroxytamoxifen, LY 117018, U 23469M, and ICI 164384 were 15-30-fold more effective in inhibiting E2-stimulated transcription by mutants KKN-QQD and KK-QQ compared to the wild-type receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
The purified estrogen receptor (ER) whether in 9 or 5 S molecular form, binds more than one molecule of the monoclonal antibody JS 34/32 (Redeuilh, G., Moncharmont, B., Secco, C., and Baulieu, E.-E. (1987) J. Biol. Chem. 262, 6969-6975). We now have investigated the effects of controlled trypsin proteolysis and of a dissociating chaotropic salt (NaSCN) on the structure of the estrogen receptor covalently labeled with radioactive tamoxifen aziridine. When the DNA-binding transformed 5S ER was dialyzed against a buffer containing 0.5 M NaSCN, it was converted into a form sedimenting at 3.7 S +/- 0.1 (n = 3). It reverted to the 5 S molecular form when NaSCN was dialyzed away. Fluorographic analysis of both the 5 and 3.7 S ER following SDS-gel electrophoresis revealed one main band corresponding to Mr congruent to 66,000. After limited trypsin treatment of the 5 S ER, tamoxifen aziridine-binding protein sedimented at 4.3 S +/- 0.1 (n = 5), had a Stokes radius of 3.6 nm (calculated Mr = 65,000), and did not bind DNA. The same form was obtained after limited trypsin digestion of the ER bound to DNA-cellulose or to hsp 90 (the nontransformed 8-9 S ER molecular form). This 4.3 S trypsinized ER was reversibly dissociated by NaSCN into a congruent to 3 S +/- 0.1 (n = 3) molecular form. Fluorographic analysis of both the 4.3 and 3 S ER after SDS-gel electrophoresis showed one main radioactive band of Mr congruent to 30,000. Taken together our results suggest that 1) the 5 S ER is a homodimer of two Mr congruent to 66,000 hormone binding subunits which may be released as such from the nontransformed 8-9 S ER, 2) the trypsin digestion products yield two carboxyl-terminal fragments of Mr congruent to 30,000 that remain in the form of a dimer having lost their DNA-binding region, and 3) the trypsin cleavage would occur within the region located between the hormone-binding domain and the DNA-binding domain. These data indicate that the dimerization of the receptor occurs through hydrophobic interaction of its hormone-binding domain but cannot exclude that other part(s) of the receptor may also contribute to the dimer formation. The dimerization may be critically involved in the mechanism by which estradiol-receptor complexes promote change of gene transcription.
The specificity of antisera produced in rabbits for use in mitomycin C (MMC) enzyme immunoassay has been examined employing competitive experiments using several mitomycin analogs and the chemically or biologically degraded preparations of MMC. These studies demonstrate that the antiserum distinguished alterations in the chemical structure of the molecule, showing decreased immunoreactivity with mitomycin A (7.8%) and B (0.78%). On the other hand, porfiromycin and acetyl MMC (Ac-MMC), which commonly possess the substituted groups (methyl and acetyl groups, respectively) at the aziridine ring, showed enhanced reactivity with the antiserum (about two times and ten times as compared to the parent MMC, respectively), suggesting that the antigen used for antibody production was the MMC acylated at the imino group of the aziridine ring. The values of the chemically or biologically degraded preparations of MMC quantified by this enzyme immunoassay were in good agreement with those of the remaining nonreacted MMC measured spectrophotometrically, thus indicating that the anti-MMC antiserum hardly cross-reacted with these degradation products.
The enzyme nitroreductase from E. coli can reduce the weak, monofunctional alkylating agent 5-(aziridin-1-yl)-2, 4-dinitrobenzamide (CB1954) to a potent cytotoxic species that generates interstrand crosslinks in DNA. Nitroreductase therefore has potential as a "suicide enzyme" for cancer gene therapy, as cells that express nitroreductase become selectively sensitive to the prodrug CB1954. We have incorporated a nitroreductase expression cassette into a replication-defective adenovirus vector (Ad-CMV-ntr), which allowed efficient gene transfer to SK-OV-3 or IGROV-1 ovarian carcinoma cells. Nitroreductase levels increased in line with multiplicity of infection, and this was reflected in increasing sensitisation of the cells to CB1954, reaching an optimum (approx. 2, 000-fold sensitisation) with 25-50 p.f.u. per cell. Similar Ad-CMV-ntr-dependent sensitisation to CB1954 was seen in 3 of 6 low-passage primary ovarian tumour lines. Cells grown at low-serum concentration to inhibit proliferation remained equally susceptible to the Ad-CMV-ntr-dependent cytotoxicity of CB1954, indicating a distinct advantage over retroviral gene delivery and other popular enzyme-prodrug systems for human tumours with a low rate of cell proliferation. Additionally, cisplatin-resistant cells were sensitised towards CB1954 by Ad-CMV-ntr as efficiently as the parental cells, indicating that the system could be effective in patients with cisplatin-resistant tumours. In a murine xenograft model for disseminated peritoneal carcinomatosis with ascites, treatment of nude mice bearing intraperitoneal SUIT2 tumours with Ad-CMV-ntr and CB1954 almost doubled the median survival from 14 to 26 days (p < 0.0001).
The mass spectrometric behaviour of six cis- and trans-1a, 3-disubstituted 1,1-dichloro-1a,2,3,4-tetrahydro-1H-azirino[1,2-a][1, 5]benzodiazepines has been studied with the aid of mass-analysed ion kinetic energy spectrometry and exact mass measurements under electron impact ionization. All compounds show a tendency to eliminate a neutral propene or styrene molecule from the diazepine ring and to simultaneously eliminate a chlorine atom from the aziridine ring to yield azirino[1,2-b][1,3]benzimidazole ions, and to lose hydrogen chloride plus propene or styrene to give quinoxaline ions. All compounds also show a tendency to eliminate N=CCl(2) or HN=CCl(2) to produce dihydro- or tetrahydroquinoline ions, and to eliminate sequentially hydrogen chloride and a chlorine atom to yield pyrrolo[1,2-a][1, 3]benzimidazole ions.
The mass spectrometric behaviour of eight 1a,3-disubstituted 1, 1-dichloro-1,1a,2,3-tetrahydroazirino[2,1-d][1,5]benzothiazepines has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and exact mass measurements under electron impact ionization. All compounds show a tendency to eliminate a chlorine radical from the aziridine ring and then eliminate a neutral propene or substituted/unsubstituted styrene from the thiazepine ring to yield 1,4-benzothiazine ions. They can also lose hydrogen chloride and a chlorine radical, or lose two chlorine atoms, to undergo a ring enlargement rearrangement to produce 1,6-benzothiazocine ions, which can further eliminate propyne or phenylacetylene, or small molecular fragments, to yield some abundant fragment ions.
2-Phenylindole derivative 8, linked to aziridine by a hexamethylene spacer group, was synthesized and tested. It binds to the estrogen receptor with an RBA-value of 4.0 (estradiol = 100). In vitro, it shows a selective cytostatic activity in hormone-dependent MCF-7 breast cancer cells (41% T/C at 10(-6) M). In vivo, it exerts a strong estrogenic effect. The binding to the estrogen receptor is largely reversible.