The Shu complex prevents mutagenesis and cytotoxicity of single-strand specific alkylation lesions

Three-methyl cytosine (3meC) are toxic DNA lesions, blocking base pairing. Bacteria and humans express members of the AlkB enzymes family, which directly remove 3meC. However, other organisms, including budding yeast, lack this class of enzymes. It remains an unanswered evolutionary question as to how yeast repairs 3meC, particularly in single-stranded DNA. The yeast Shu complex, a conserved homologous recombination factor, aids in preventing replication-associated mutagenesis from DNA base damaging agents such as methyl methanesulfonate (MMS). We found that MMS-treated Shu complex-deficient cells exhibit a genome-wide increase in A:T and G:C substitutions mutations. The G:C substitutions displayed transcriptional and replicational asymmetries consistent with mutations resulting from 3meC. Ectopic expression of a human AlkB homolog in Shu-deficient yeast rescues MMS-induced growth defects and increased mutagenesis. Thus, our work identifies a novel homologous recombination-based mechanism mediated by the Shu complex for coping with alkylation adducts.

The Akoya pearl oyster shell as an archival monitor of lead exposure

The Akoya pearl oyster (Pinctada imbricata) was experimentally exposed to (a) constant levels of lead (Pb) at 180 microg L(-1) for nine weeks, or (b) two short term (pulse) exposures of Pb at 180 microg L(-1) (three weeks each) with an intervening depuration period (three weeks), to assess its utility as an (i) accumulative monitor of Pb contamination and an (ii) archival monitor for discriminating constant versus pulsed Pb exposure events. P. imbricata showed similar reductions in growth (based on shell morphology and wet weight) and Pb accumulation patterns for whole tissue and shell in response to both Pb exposure regimes. Thus the whole oyster was deemed an inappropriate accumulative monitor for assessing short-term temporal variation of Pb exposure and effect. However, using secondary ion mass spectrometry, Pb was shown to accumulate in the successively deposited nacreous layers of the shell of P. imbricata, documenting the exposure history of constant versus pulsed Pb events. Patterns of Pb deposition not only reflected the frequency of Pb exposure events but also their relative durations. Thus, the shell of P. imbricata may be employed as a suitable biological archive of Pb exposure.

Transient foamy virus vector production by adenovirus vectors

The genome of the prototype foamy virus (PFV) has been introduced into an adenoviral/PFV hybrid vector and tested for stable in vitro gene transfer. Three different adenoviruses are used to encode: (i) the PFV structural genes gag and pol (Ad-GagPolDeltaPacI); (ii) the PFV structural gene env (Ad-Env); and (iii) the PFV vector genome (Ad-MD9) encoding the transgene (the enhanced green fluorescent protein (eGFP) gene). Following cotransduction by the three adenoviruses, the target cells become transient PFV vector-producing cells, resulting in the in situ release of recombinant PFV at a titre of up to 10(3) vector particles/ml, which can then infect surrounding cells, leading to stable integration of the expression cassette. Stable eGFP expression, observed for up to 60 days (11 passages) in cells transduced with all three adenoviral vectors, was shown by PCR to be the result of PFV integration. In contrast, cells transduced with only the adenovirus encoding the PFV vector genome showed a marked decrease in eGFP expression by passage 2 (16 days post-transduction) and did not contain integrated PFV vector. In short, this paper describes the production of a hybrid vector capable of high in vitro transduction and stable transgene expression using adenovirus and PFV vectors.

Human foamy virus integrase fails to catalyse the integration of a circular DNA molecule containing an LTR junction sequence

The presence of closed circular forms of the linear DNA genome of human foamy virus (HFV) has not been established. The ability of the HFV integrase (IN) to catalyse the integration of these circular forms (termed 2 long terminal repeat (LTR) circles) was investigated, with a view to producing a novel hybrid vector. To this end, a construct was made containing, in addition to the enhanced green fluorescent protein (eGFP) marker gene, the last 27 bp of the 3' U5 LTR region of HFV fused to the first 28 bp of the 5' U3 LTR, the latter representing a 2LTR circle. Marker gene expression following transfection of both 293 and 293T cells indicated that the level of integration was not significantly increased by the HFV IN. Moreover, correctly integrated provirus-like forms of the input plasmid could not be detected by PCR. Taken together, these results show that the HFV IN is not able to integrate a circular molecule containing an LTR junction and, hence, the technique is not exploitable as a tool to produce hybrid vectors for gene therapy.

Incorporation of a molecular hinge into molecular tweezers by using tandem cycloadditions onto 5,6-dimethylenenorbornene

Site-selective 1,3-dipolar coupling at the norbornene pi-bond of 5,6-dimethylenenorbornene 1 yields cycloadducts with an end-fused 1,3-diene system which have been reacted with N=N (or C=C) dienophiles to produce ribbon molecules, in which the internal diazacyclohexene (or cyclohexene) subunits are capable of acting as conformational hinges. Direct coupling of 5,6-dimethylenenorbornene with 1,3,4-oxadiazoles or dual coupling with bis(cyclobutene epoxides) afforded bis(1,3-dienes) that diastereoselectively react with dienophiles to produce new, conformationally mobile, molecular tweezers.

The R region found in the human foamy virus long terminal repeat is critical for both Gag and Pol protein expression

It has been suggested that sequences located within the 5' noncoding region of human foamy virus (HFV) are critical for expression of the viral Gag and Pol structural proteins. Here, we identify a discrete approximately 151-nucleotide sequence, located within the R region of the HFV long terminal repeat, that activates HFV Gag and Pol expression when present in the 5' noncoding region but that is inactive when inverted or when placed in the 3' noncoding region. Sequences that are critical for the expression of both Gag and Pol include not only the 5' splice site positioned at +51 in the R region, which is used to generate the spliced pol mRNA, but also intronic R sequences located well 3' to this splice site. Analysis of total cellular gag and pol mRNA expression demonstrates that deletion of the R region has little effect on gag mRNA levels but that R deletions that would be predicted to leave the pol 5' splice site intact nevertheless inhibit the production of the spliced pol mRNA. Gag expression can be largely rescued by the introduction of an intron into the 5' noncoding sequence in place of the R region but not by an intron or any one of several distinct retroviral nuclear RNA export sequences inserted into the mRNA 3' noncoding sequence. Neither the R element nor the introduced 5' intron markedly affects the cytoplasmic level of HFV gag mRNA. The poor translational utilization of these cytoplasmic mRNAs when the R region is not present in cis also extended to a cat indicator gene linked to an internal ribosome entry site introduced into the 3' noncoding region. Together these data imply that the HFV R region acts in the nucleus to modify the cytoplasmic fate of target HFV mRNA. The close similarity between the role of the HFV R region revealed in this study and previous data (M. Butsch, S. Hull, Y. Wang, T. M. Roberts, and K. Boris-Lawrie, J. Virol. 73:4847--4855, 1999) demonstrating a critical role for the R region in activating gene expression in the unrelated retrovirus spleen necrosis virus suggests that several distinct retrovirus families may utilize a common yet novel mechanism for the posttranscriptional activation of viral structural protein expression.

Palindromic sequence plays a critical role in human foamy virus dimerization

The retroviral RNA genome is dimeric, consisting of two identical strands of RNA linked near their 5' ends by a dimer linkage structure. Previously it was shown that human foamy virus (HFV) RNA transcribed in vitro contained three sites, designated SI, SII, and SIII, which contributed to the dimerization process (O. Erlwein, D. Cain, N. Fischer, A. Rethwilm, and M. O. McClure, Virology 229:251-258, 1997). To characterize these sites further, a series of mutants were designed and tested for their ability to dimerize in vitro. The primer binding site and a G tetrad in SI were dispensable for dimerization. However, a mutant that changed the 3' end of SI migrated slower on nondenaturing gels than wild-type RNA dimers. The sequence composition of the SII palindrome, consisting of 10 nucleotides, proved to be critical for in vitro dimerization, since mutations within this sequence or replacement of the sequence with a different palindrome of equal length impaired in vitro dimerization. The length of the palindrome also seems to play an important role. A moderate extension to 12 nucleotides was tolerated, whereas an extension to 16 nucleotides or more impaired dimerization. When nucleotides flanking the palindrome were mutated in a random fashion, dimerization was unaffected. Changing the SIII sequence also led to decreased dimer formation, confirming its contribution to the dimerization process. Interesting mutants were cloned into the infectious molecular clone of HFV, HSRV-2, and were transfected into BHK-21 cells. Mutations in SII that reduced dimerization in vitro also abolished virus replication. In contrast, constructs containing mutations in SI and SIII replicated to some extent in cell culture after an initial drop in viral replication. Analysis of the SIM1 mutant revealed reversion to the wild type but with the insertion of an additional two nucleotides. Analysis of cell-free virions demonstrated that both replication-competent and replication-defective mutants packaged nucleic acid. Thus, efficient dimerization is a critical step for HFV to generate infectious virus, but HFV RNA dimerization is not a prerequisite for packaging.

Sudden death due to metronidazole/ethanol interaction

Metronidazole (Flagyl), a commonly prescribed antimicrobial agent, can produce a reaction similar to that of disulfiram (Antabuse) when administered to patients drinking ethanol. This drug/chemical interaction results in accumulation of acetaldehyde in the blood. Acetaldehyde is hepatotoxic, cardiotoxic, and arrythmogenic; no lethal serum acetaldehyde level has been established. Sudden death has been reported in patients taking disulfiram while using ethanol; no fatalities have been reported due to ethanol/ metronidazole interactions. Described is a case of a 31-year-old woman who died moments after an assault by a male companion, during which he inflicted minor physical trauma to her upper arm. Toxicologic analysis yielded elevated concentrations of serum ethanol (162 mg/d), acetaldehyde (4.6 mg/d), and metronidazole (0.42 mg/L). The cause of death was reported to be cardiac dysrhythmia due to acetaldehyde toxicity due to an ethanol/ metronidazole interaction. Autonomic stress associated with the assault is likely to have contributed to this woman's death. The mechanism of death is examined.

Maleimide-Fused Cyclobutadienes and Dewar Furans: Trapping With Dienes as a Route to Propellane Photosubstrates With Potential for Oxiren Production

N-Methylmaleimide-fused cyclobutadiene (15) and its 1,2-dimethyl derivative (41) have been generated by zinc/titanium tetrachloride treatment of the vicinal dibromide (39) and (24) respectively. Prior epoxidations of (24) and (39) produce mixtures of dibromo epoxides which yield the related N-methylmaleimide-fused Dewar furans (16) and (17) upon similar debromination (Zn/TiCl4). None of these reactive intermediates is sufficiently stable for direct observation, but each was trapped in adduct form by Diels-Alder reaction with furan. Attempts to form fused Dewar furan (17) by flash vacuum pyrolysis of the furan adduct (34) led to the production of the isomeric furo [3,4-c] pyrrole (43), the structure of which was confirmed by separate synthesis. Stereochemical assignments have been made to most adducts, and AM1 calculations have been used to predict the stereoselectivities and facial selectivities in these cycloaddition reactions. Reaction of these Dewar furans with cyclopentadienones produced propellanes which were decarbonylated to their respective cyclohexadienes and used as photosubstrates for the generation of oxiren or dimethyloxiren . Attempts to trap oxiren, generated by photolysis of propellane (12), with isobenzofuran were unsuccessful.

A 19F NMR study of the interaction of 3-fluoro-4-demethoxydaunomycin with the hexanucleotide d(TCCGGA)2

19F NMR spectroscopy has been used to study the binding of the fluorinated anthracycline 3-fluoro-4-demethoxydaunomycin with the hexanucleotide d(TCCGGA)2. In the spectrum of the 1:1 anthracycline-d(TCCGGA)2 complex four resonances of approximately equal intensity were observed. This indicated that 4-demethoxydaunomycin intercalated at all possible sites with similar affinity. This suggests that the specific high affinity binding sites that are observed in anthracycline-DNA footprinting experiments are strongly regulated by the local DNA conformation.

The Photochemical Generation of Isoindene and Its Dimerization to Diastereomeric 1-(Indian-1-yl)indenes

Isoindene (1), generated by ultraviolet irradiation ( Vycor filter, acetone solution) of 1,4- dihydro-1,4-methanonaphthalene-2,3-dione (14), is shown to undergo homodimerization at -60°. This cycloaddition involves the intermolecular transfer of a hydrogen atom from one isoindene molecule to a second isoindene molecule in an [(8π+2σ)+ Sπ ] pericyclic process. The gross structure of the resulting diastereomeric dimers was confirmed by synthesis from 1-bromoindan (25) and indenyl anion (26). The stereochemistry of the dimers was determined by comparing their dihydro derivatives (33) and (34) with authentic samples. The authentic samples were themselves prepared by cis hydrogenation (Pd/C) of (E)-2,2′,3,3′-tetrahydro-1,1′-bi-1H-indenylidene (30) which yielded (34), and trans hydrogenation (Na/NH3) of (30) which formed (33) together with (34) (ratio 7:3). The (E) stereochemistry of (30), which was a critical feature in the stereochemical assignments to (33) and (34), was confirmed by n.O.e. studies on it and its (D4)derivative (32). Complete analysis of the proton, proton coupling was conducted on (32). This identified a 5J coupling between protons C 3-H and C 7-H which contributed a 6% scalar coupling to the observed n.O.e . of 39% at C 7-H. This information allowed unambiguous stereochemical assignments to be made to (33). The chirality of 1,1′-bi-1H-indenyls (43) and (44), prepared by the radical coupling of 1H-inden-1-ylmagnesium bromide, was also determined by a similar hydrogenation process.

The Photochemistry of Isobenzofuran. I. Structure of the Dimers Resulting From Ultraviolet Irradiation of Isobenzofuran in Acetone and Ether Solution

Irradiation of isobenzofuran (1) in acetone solution yields a symmetrical [π8s+π8s] dimer (24) involving bonding at the peri -position of the furan moiety in each molecule. The anti-stereochemistry of this dimer was established by a novel application of lanthanide induced shift spectroscopy. In contrast, irradiation of isobenzofuran (1) in ether solution yielded the unsymmetrical dimer (34) as the major product, together with lesser amounts of the symmetrical dimer (24), and small amounts of a new dimer (50) resulting from [π8s+π4s] cycloaddition , where the 8π system of the isobenzofuran of one molecule reacts with the carbocyclic 4π diene of the other. The structure of the unsymmetrical dimer (34) was confirmed by synthesis. No evidence for the Dewar form (7e) of isobenzofuran could be obtained in these reactions conducted at -60° and monitored by 1H n.m.r. spectroscopy. However, the small, but persistent, production of o-phthalaldehyde may implicate an intermediate derived from (7e).

Reaction of Dienophiles With a 5,6-Bismethylenenorborn-2-en-7-one: the Synthesis of a Stable Norborna-2,5-dien-7-one

Reaction of hemicyclone (10) with (E)-1,4-dibromobut-2-ene (9) under forcing conditions yielded a 1:1 adduct (11) which served as the precursor for the 5,6-bismethylenenorborn-2-en-7-one (12) through fluoride-promoted dehydrobromination. The conjugated diene group in (12) enters into Diels-Alder reactions with reactive dienophiles to produce intermediate norbornadienones en route to aromatic products. It has been possible to identify the norborna-2,5-dien-7-one (16) resulting from the reaction of (12) with N- tolyltriazoline dione (15), thereby offering authentic evidence for the rare norborna-2,5-dien-7-one ring system. In addition, (12) has been used as a reagent to evaluate facial selectivity in its reaction with the transient Dewar benzene (24). The cyclobutamaleimide moiety in (24) is screened on each face, yet facial discrimination in its reaction with (12) is high (7: 1). Thermolysis of the 5,6-bismethylenenorborn-2-en-7-one (12) yields the substituted benzocyclobutene (14), a reaction which may involve the o-xylylene (13) as intermediate.

The Adducts of Isobenzofuran and cis-3,4-Dichlorocyclobutene, and Their Conversion Into Formal Dewar Furan Adducts

cis-3,4-Dichlorocyclobutene (19) reacts with isobenzofuran (4) to produce three of four possible [ π;45+π 28] cycloaddition products. The isomer (27) is the dominant cycloadduct , which indicates that significant stabilization by the chlorine atoms with isobenzofuran occurs in the transition state leading to this product. Both adducts (26) and (27) are dechlorinated to form the exo cyclobutene (31), and the other adduct, the isomer (28), yields the endo cyclobutene (33); these products correspond to the formal adducts of cyclobutadiene with isobenzofuran . Separate reactions of cyclobutenes (31) and (33) with 3-chloroperbenzoic acid produce a single anti epoxide in each case, (32) and (34), respectively; these products are identical with the pair of isobenzofuran adducts derived from Dewar furan itself, as reported elsewhere.

Acetylene Stacking: a New Concept for the Synthesis of Cyclic Polyenes. Application to the Preparation of a 1,6-Bridged Bicyclo[4.2.0]octa-2,4,7-triene and Some Novel Oxepins

A new protocol for a general synthesis of cyclic polyenes is presented; in this protocol two new concepts are introduced. The first, acetylene stacking, is the generic term covering both the synthesis of a target molecule and the specific retrosynthesis upon which it is based. This retrosynthetic analysis involves conversion of the target molecule, through a series of transannular [ π2s+π2s] valence isomerizations , into a key polycyclobutanoid intermediate (24). This intermediate is cleaved, in turn, through a similar number of [ σ2s+ σ2s] electrocyclic fragmentations, to yield a set of acetylene synthons . The synthetic phase is based on the recombination of the corresponding acetylene synthetic equivalents in a stacking mode which leads to the target molecule by way of the same polycyclobutanoid intermediate (24). To achieve the ordered assembly of the acteylene synthons, in the required stacking mode, it has been necessary to develop the second concept, namely transfer technology. This involves the use of special transfer reagents, to act as synthetic equivalents and provide the molecular equivalent of acetylenes without ever producing acetylenes per se. Similar transfer reagents are described for cyclobutadienes which serves to demonstrate the wider implications of this new concept in organic synthesis. The bridged bicyclic polyene 8-oxatricyclo [4.3.2.01,6]undeca-2,4,10-triene (73), and the heterocycle 2,4,5,7,8-pentamethyl-1H-oxepino[4,5-c]pyrrole-1,3(2H)- dione (91) are used as the target molecules to illustrate this new synthesis protocol involving sets of stacked acetylenes (or cyclobutadienes ) as the synthetic base. The conversion of the oxepin (91) into isomeric oxepins, and the role of their tautomeric benzene oxides, present as equilibrium partners, is discussed.

The Preparation of Dimethyl (1-α,2-β,5-β,6-α)-9-Oxatricyclo[4.2.1.02,5]nona-3,7-diene -3,4-dicarboxylate: a New Transfer Reagent for Dimethyl Cyclobutadiene-1,2-dicarboxylate

A synthesis, based on transfer technology, of the title compound is reported and its advantages over previously described reagents are discussed.

New Thermal and Photochemical Routes to Dewar Furan and Other Isomers on the C4H4O Energy Surface: the Role of Isobenzofuran as a Trapping Agent

Photolysis of the specially synthesized substrate (39) leads to quantitative fragmentation into the phthalimide (56) and Dewar furan (4a). Dewar furan has only transient existence even at -65°, yet can be trapped effectively with isobenzofuran but not furan. Rapid isomerization to cycloprop-2-enecarbaldehyde (57) occurs at the photolysis temperatures and this product is also trapped by the isobenzofuran . In the absence of trapping agent, photolysis of (39) produces some furan but no 1H n.m.r . evidence can be obtained for (4a) or (57), even at low temperatures (-85°). Separate irradiation of (57) causes extensive polymerization, without yielding other recognizable products. Furan is concluded, therefore, to arise from photoisomerization of (4a) rather than photochemical or thermal isomerization of (57). Separate thermal study of (57) shows that isomerization to furan only occurs above 420°. Flash vacuum pyrolysis of the polycyclic epoxide (72) provides a new retro- Diels-Alder route to (57) which likely proceeds via (4a) as an intermediate. At high temperatures (57) is isomerized to furan. A new Dewar benzene oxide (41) and Dewar benzene (45) are reported en route to the photosubstrates (39) and (50) respectively. Photolysis of (50) provides a high-yielding source of cyclobutadiene , which in the absence of trapping agent yields the syn-dimer (59).

The Synthesis of Bisanthraquinones Joined by Polyether Linkages

Derivatives of quinizarin linked by polyether chains have been prepared by the annelation of bis (quinone monoacetals) with the anions of substituted 3-cyanophthalides.

Towards the Synthesis of a Dewar Furan Stabilized by a Pinching Group: the Role of Dewar o-Xylylenes as Dienes and Dienophiles

The synthesis of a photosubstrate (42) suitable for the production of a Dewar furan (46) containing a four-carbon bridge at the 1,4-position is described. The route to this product illustrates an example of transfer technology in synthesis, by using the oxanorbornadiene (29). Other active species such as Dewar benzene (32) and Dewar o-xylylene (50) play key roles as intermediates. Diels-Alder cycloadditions are also central to the overall strategy, and some observations are made regarding the facial specificities operating, especially in regard to Dewar o-xylylene (50) and its dimerization. Attempts to isolate the photoproducts, presumably involving the Dewar furan (46) as intermediate, were unsuccessful.

Anodic-Oxidation Products of 2',5'-Dimethoxyacetanilide Derivatives, and Their Application to the Synthesis of Aminoanthraquinones

Anodic oxidation of simple 2′,5′-dimethoxyacetanilides proceeds under mildly basic conditions to afford either monomeric or dimeric quinone bisacetals, depending on the structure of the substrate. Similarly, the oxidation of linked derivatives of 2′,5′-dimethoxyacetanilides is shown to exhibit a comparable sensitivity, with non-alkylated amides being efficiently converted into bis(quinone bisacetals). The regiospecificity of acetal hydrolysis for both simple and linked quinone bisacetals is shown to be dependent upon the nature of the N-acyl group. The annelation of these hydrolysis products with the anion of 3-cyanophthalide to yield (acylamino)anthraquinones is also reported.

A 19F-NMR study of 3-fluoro-4-demethoxydaunomycin intercalation complexes with the hexanucleotide d(CTGCAG)2

Equilibrium systems containing intercalation complexes formed between the novel anthracycline drug, 3-fluoro-4-demethoxydaunomycin (3FD), and the hexanucleotide duplex d(CTGCAG)2 have been studied by 19F-NMR spectroscopy. Solutions containing a 1:1 molar ratio of 3FD/d(CTGCAG)2 gave four 19F signals which have been assigned to each of four possible intercalation isomers for the 1:1 3FD.d(CTGCAG)2 complex, which we denote by [d(CTGCAG)2][3FD]; these were where 3FD bound between the 5'-CT-3', 5'-TG-3', 5'-GC-3' or 5'-CA-3' base sequences, with the drug sugar moiety lying in the minor groove and pointed in the 3' direction in each case. Changes in temperature and NaCl concentration affecting the equilibrium distribution of these isomers were studied and indicated that no overriding binding site preference prevailed under standard biochemical conditions. Formation of some of the 2:1 3FD.d(CTGCAG)2 complex occurred when a solution of [d(CTGCAG)2][3FD] was exposed to excess 3FD; however, this complex was unstable to gel filtration and no co-operative binding of the second 3FD molecule was observed.

Effects of solute conditions on the relative affinities of the oligonucleotides d(G-C)5 and d(A-T)5 for the anthracycline drug 2-fluoro-4-demethoxydaunomycin

19F NMR has been used to show that changes in NaCl concentration, as well as the presence of lysine or arginine, affect the equilibrium distribution of the synthetic anthracycline 2-fluoro-4-demethoxydaunomycin (2FD) between binding sites on d(G-C)5 and d(A-T)5 in a 1:1:1 molar aqueous system: 2FD/d(G-C)5/d(A-T)5. Varying the pH between 6.2 and 7.7 had no effect. NaCl concentrations below 0.1 M led to a d(G-C)5 preference while above 0.1 M a preference for d(A-T)5 was observed. At comparable solute concentrations, use of either lysine or arginine resulted in a significant drug preference for d(G-C)5 compared to systems containing only NaCl.

A 19F-NMR study of 2-fluoro-4-demethoxydaunomycin intercalation complexes with the decanucleotides d(G-C)5 and d(A-T)5

Binding configurations and equilibria of intercalation complexes formed by the novel anthracycline drug, 2-fluoro-4-demethoxydaunomycin (2FD), with the decanucleotides d(G-C)5 and d(A-T)5 have been studied by 19F-NMR spectroscopy. The 19F chemical shift of 2FD bound to d(A-T)5 was approximately 1.5 ppm downfield of that observed for 2FD bound to d(G-C)5. By mixing equimolar amounts of aqueous d(G-C)5, d(A-T)5 and 2FD, the distribution of drug between the nucleotides was followed by observing relative peak intensities and showed no G-C or A-T binding preference at room temperature. It was shown that each decanucleotide duplex bound three 2FD molecules, giving a neighbour exclusion parameter, n, of n = 3 for this drug. The stoichiometric complexes, which we denote by [d(A-T)5][2FD]3 and [d(G-C)5][2FD]3, were also purified and isolated in this study.

Anthracyclines. XVI. Further Comments Concerning the Phthalide Anion Annelation of Quinone Monoacetals

.Yields of tricyclic and tetracyclic quinones prepared by annelation of quinone monoacetals with the anion of 3-phenylsulfonylphthalides are shown to be sensitive to the substituent on both the phthalide and the quinone monoacetal partner. In contrast, reactions with the anions of 3-cyanophthalides afford high yields of condensed products in all cases examined.

Anthracyclines. XIII The Synthesis of (+)-(4R,6R)- and (+)-(4S,6R)-6-Acetyl-6-(t-butyldimethylsilyloxy)-4-ethoxy-4-methoxy-5,6,7,8-tetrahydronaphthalen-1(4H)-one: New Chiral AB Synthons for the Synthesis of (—)-7-Deoxydaunomycinone

The title dienones have been prepared from (-)-(2R,1′S)-8-benzyloxy-2-(1′-hydroxyethyl)-5-methoxy-1,2,3,4-tetrahydronaphthalen-2-ol, by a series of reactions in which the selective cleavage of an aryl methyl ether in the presence of an aryl ethyl ether plays a key role. This 10- step sequence proceeds in an overall yield of 55%, and chiral integrity is preserved throughout.

Anthracyclines. XII. The preparation of (—)-(7R)-7-Acetyl-7-(t-butyldimethylsilyoxy-1(4H)-one and (+)-(6R)-6-Acetyl-6-(t-butyldimethylsilyloxy)- 4,4-dimethoxy-5,6,7,8-tetrahydronaphthalene-1(4H)-one: an Improved Route to Chiral AB Synthons for 7-Deoxydaunomycinone

The title dienones (2) and (5) were prepared from the chiral alcohols (7a) and (7b) respectively. These key starting materials were in turn available from the reduction of 3-acetyl-5-benzyloxy-8-methoxy-1,2- dihydronaphthalene (6a) and 3-acetyl-8-benzyloxy-5-methoxy-1,2- dihydronaphthalene (6b) with lithium aluminium hydride modified with (—)-N- methylephedrine and N- ethylaniline . Chiral phase high-pressure liquid chromatography was used to analyse the enantioselectivity of these reductions which were shown to yield variable results depending upon the origin of the reducing agent.

Pinching group stabilization. The synthesis and thermal isomerization of 10-Oxapentacyclo[6.3.2.13,6.01,8.02,7]tetradeca-4,12-diene

Sensitized irradiation (benzophenone, 0�, N2, pyrex filter, medium pressure Hg lamp) of dimethyl tricyclo[4.2.1.02,5]nona-3,7-diene-3,4-dicarboxylate (11) in (E)-1,2-dichloroethene yielded a mixture of 1 : 1 adducts (13) and (14) by site selective [2 π+2 π] cycloaddition at the cyclobutene π-bond. Reduction of the (Z)-dichloro isomer(13) with lithium aluminium hydride formed the related diol (16) which is the immediate precursor to the cyclic ether (18). Dechlorination of (18) with zinc in ethanol forms the title diene (19). Thermolysis of the polycyclic diester (20) affords the fragmentation products cyclopentadiene and dimethyl benzene-1,4-dicarboxylate. In contrast, the title compound (19) containing the cyclic ether ring was more stable and yielded the novel isomer (28) as the major product only upon flash vacuum pyrolysis at 560�(1.5 × 10-2 Torr). This difference in behaviour is attributed to a pinching group effect exerted by the cyclic ether present in (19).

Anthracyclines. XI. A short, site-specific synthesis of unsymmetrical 3-Acetyl-5,8-dialkoxy-1,2-dihydronaphthalenes; key precursors to daunomycinone AB-synthons

5,8-Dihydronaphthalene-1,4-diol, readily available from benzoquinone and buta-1,3-diene, is isomerized by heating with strong sodium hydroxide, and acetylated (Ac2O), in situ, to form 5,8-diacetoxy-1,2-dihydronaphthalene. Catalysed (AlCl3) addition of acetyl chloride followed by dehydrochlorination (LiCI/HCONMe2) yielded 5,8-diacetoxy-3-acetyl-1,2-dihydronaphthalene (11) in 82% overall yield. Base hydrolysis of (11), followed by methylation (Me2SO4) gives 3-acetyl-5,8-dimethoxy-1,2-dihydronaphthalene in 94% yield, the most direct route to this product so far described. More importantly, the diacetate (11) is selectively deacetylated at C5 (Cs2CO3 in tetrahydrofuran, or K2CO3 in Me2SO) to form the related phenol, alkylation of which produces the 5-alkoxy compound. Further hydrolysis followed by alkylation yields the unsymmetrically, but regiospecifically substituted, 3-acetyl-5,8-dialkoxy-1,2-dihydronaphthalenes. This method is specifically illustrated by the production of 3-acetyl-5-benzyloxy-8-methoxy-1,2-dihydronaphthalene which is formed in a short, cost effective synthesis in a moderate overall yield (25%) based upon benzoquinone as starting material;significantly, no chromatographic separations are required.

Anthracyclines. X. The enantiospecific synthesis of ( - )-(7R)-7-Acetyl-7-hydroxy- 4,4-dimethoxy-5,6,7,8-tetrahydronaphthalen-1(4H)-one; a type I chiral dienone for the synthesis of 7-Deoxydaunomycinone

8-Benzyloxy-5-methoxy-3,4-dihydronaphthalene-2-carboxylic acid (34) has been prepared by a four-step sequence from 5-methoxy-8-hydroxy-3,4-dihydronaphthalen-1(2H)-one. Condensation of the unsaturated acid (34) with ethyl (S)-prolinate in the presence of dicyclohexylcarbodiimide afforded the amide (35) which was enantioselectively cyclized to the bromo lactone (37). Debromination with tributyltin hydride and subsequent reaction of the lactone with methyllithium afforded (-)-(2R)-2-acetyl-8-benzyloxy-5-methoxy-1,2,3,4-tetrahydronaphthalen-2-ol. Removal of the benzyl ether by catalytic hydrogenation and oxidation of the resulting phenol with thallium(III) nitrate afforded the title chiral dienone.

A practical route to alcohols in the 7,7-Dimethylbenzonorbornene (9,9-Dimethyl-1,4-methanonaphthalene) series

The previously undescribed exo-and endo-7,7-dimethylbenzonorbornen-5-ols, can be prepared by the selective hydrogenolysis of the central unsubstituted bond in the corresponding spirocyclopropyl derivatives. Other examples of the reaction are also described.

The regiospecific synthesis of an anthraquinone based upon the elaboration of the adduct of 1-acetoxyisobenzofuran with p-benzoquinone monoacetal

1-Acetoxyisobenzofuran (4) reacts regiospecifically with 4,4-dimethoxycyclohexa-2,5-dienone (p-benzoquinone monoacetal) (6) to yield a single [4π+2π] cycloadduct with endo stereochemistry. Treatment of this adduct (7) with sodium methoxide formed 1,10-dihydroxy-4,4-dimethoxy-4a,10- dihydroanthracen-9(4H)-one (12), which was oxidized by the Corey-Fleet reagent to afford 1-hydroxy-4-methoxyanthracene-9,10-dione. This model reaction illustrates the potential of this approach to the regiospecific synthesis of anthraquinones. Attempts to introduce methoxy substituents into the anthraquinone by using 4- and 7-methoxy-1-acetoxyisobenzofuran, isobenzofurans described for the first time, were less successful. This limitation is discussed.

The regiospecific cycloaddition of 8,8-dimethylisobenzofulvene with isobenzofuran, 1-methylisobenzofuran and 1,3-dimethylisobenzofuran

The mixed 1 : 1 adduct formed upon reaction of isobenzofuran with 8,8-dimethylisobenzofulvene is shown to have structure (5) resulting from a [10 + 8] cycloaddition in which the isobenzofulvene serves as the 10 π reagent and the isobenzofuran as the 8 π reagent. The reaction occurs stereospecifically and forms exclusively the endo adduct. Lanthanide-induced shift spectroscopy, 13C n.m.r. and 1H n.m.r. spectroscopy, and deuterium-labelling techniques have been used to establish this structure. The structure of the adducts (24) and (26) derived from 1-methylisobenzofuran and 1,3-dimethylisobenzofuran, respectively, have also been established. A PMO treatment of this reaction correctly predicts the structure of these products including the regiochemistry of the product (24) formed from 1-methylisobenzofuran.

Isobenzofulvenes. VIII. The structure of the dimers derived from 8,8-dimethylisobenzofulvene. A PMO treatment of the perispecificity in this dimerization and related cycloadditions involving isobenzofulvenes

8,8-Dimethylisobenzofulvene, generated from the reaction of ll-isopropylidenetricyclo[6,2,1,02.7]- undeca-2,4,6,9-tetraene (23) and 3,6-di(pyridin-2-yl)-s-tetrazine, undergoes spontaneous dimerization to form a mixture of two isomers. This is shown to be a mixture of endo (33) and exo isomers (37) resulting from [π10s+π8s] cyclodimerization, with the former isomer predominating. 1H and 13C n.m.r. spectroscopy, in conjunction with lanthanide shift reagents and spin decoupling, was used, together with chemical degradation, to determine the structure and stereochemistry of these products. Chemical interconversion has placed these structures on a firm basis since the structure of the minor isomer has been determined by X-ray structure analysis. The constancy of this dimer ratio in solvents of widely differing polarity, and in the absence of solvent, supports an isopolar transition state which is typical of many concerted electrocyclic processes. A complete PMO treatment of all possible modes of isobenzofulvene dimerization is presented and the results of these calculations are discussed in terms of the observed peri- and stereospecificities. In a similar way, the PMO model is successfully employed to explain the relative efficiencies of various polyenophiles in trapping the isobenzofulvene nucleus.

An investigation of the reaction of dehydrogenating agents with a stable 8-Oxatricyclo[4,3,0,07,9]nona-2,4-diene and related Bicylo[4,2,0]octa-2,4-dienes as a potential route to isobenzofurans

Reaction of the 7,8-dichlorobicyclo[4,2,0]octa-2,4-diene (9) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone yields the benzocyclobutene (10). Extension of this technique to the related bicyclo[4,2,0]octa-2,4,7-trienes (21) and (23), or 8-oxatricyclo[4,3,0,07,9]nona-2,4-diene (6) was unsuccessful. Manganese dioxide was equally unrewarding while o-chloranil reacted with these olefins to yield benzodioxins in a [4+2] cycloaddition reaction.

The preparation of a stable 8-oxatricyclo[4,3,0,07,9]nona-2,4-diene and an evaluation of its potential as a source for the photochemical generation of oxiren

The synthesis of 2-methyl-3,4,5-triphenyl-8-oxatricyclo[4,3,0,07,9]nona-2,4-diene (14) is described, the first stable member of this ring system. Preparation of (14) was achieved by reacting dibenzyl diazenedicarboxylate with 2-methyl-3,4,5-triphenylbicyclo[4,2,0]octa-2,4,7-triene (29) to form the adduct (30a), which was selectively epoxidized at the cyclobutenyl double bond with 3-chloroperbenzoic to yield the epoxide (32a). Removal of the benzyl groups (H2/Pd) from the hydrazo bridge of (32a), followed by oxidation (red mercuric oxide or hydrogen peroxide) yielded the putative azo compound (33) which spontaneously lost dinitrogen, even at -78�, to yield (14) as a crystalline solid, m.p. 128�. While (14) has the potential to undergo 1,2-photoaromatization to yield oxiren (4a), this is not realized and ring-opening to the cyclic epoxide (34) is the major photochemical reaction observed under various ultraviolet irradiation conditions. Isomerization of (14) into (34) also occurs under thermal conditions. The 1H n.m.r, spectra of (14) as well as its trapping with dienophiles is discussed.

Preparation and trapping of 1-Acetoxyisobenzofuran. The structure of a novel phthalide formed in the attempted generation of 1-Acetoxyisobenzofuran in the presence of quinones

A new potential synthesis of anthraquinones based upon 1-acetoxyisobenzofuran (4) is reported. The key reaction used to generate isobenzofurans, namely the s-tetrazine reaction, proceeds smoothly in the presence of N-methylmaleimide to yield the expected adduct (16). In contrast, the reaction takes a different path in the presence of quinones to yield a novel phthalide (15). These reactions are considered to involve a non-concerted fragmentation of the intermediate dihydro-pyridazine (3) to yield the stabilized zwitterionic species (13). The zwitterion leads on to the phthalide (15) in a two step sequence involving the quinone as oxidant, while normal fragmentation is the sole reaction in the absence of oxidant. ��� The structure of 3-[3',6'-di(pyridin-2''-yl)pyridazin-4'- yl]isobenzofuran-1(3H)-one (15) has been determined by single crystal X-ray diffraction and refined by full-matrix least squares to a residual of 0.107 for 1389 'observed' reflections. Crystals are monoclinic, P21/c, a 8.271(2), b 19.183(4), c 11.814(2)Ǻ, β 110.0(1)β.

Site- and stereo-selectivity in the reaction of bicyclo[4,2,0]octa-2,4-dienes and related 2,4,7-trienes with 3-chloroperbenzoic acid: the formation ofacid-sensitive ene-epoxides and their conversion into 1,4-epoxides

Controlled site selective peroxidation of the bicyclo[4,2,0]octa-2,4,7-trienes (1a), (1b) or the related 2,4-diene (9) by means of 3-chloroperbenzoic acid in a basic two-phase medium allows the isolation of ene epoxides; these are especially sensitive to acid and rearrange to 1,4-oxides upon treatment with commercial (D)chloroform. Regular 3-chloroperbenzoic acid peroxidation conditions yield the 1,4-oxides directly. A carbonium mechanism is proposed to account for the interconversion of the initially formed 1,2-oxides into the more stable 1,4-oxides; the benzocyclobutene and methylene alcohols isolated in some cases are accommodated within this mechanism. Structure determinations draw heavily on 13C n.m.r. spectroscopy, especially to distinguish between epoxides and 1,4-oxides. The X-ray structure of a key 1,4-Coxide (11) is presented. The concept of the steric bulk of a π-cloud is discussed in terms of its role in controlling the stereoselectivity of the epoxidation reaction.

In vitro studies of the rabbit immune system. VII. The generation of rabbit anti-mouse cytotoxic T lymphocytes

Lymphocytes from normal or immunized rabbits generated cell-mediated cytotoxic activity (CML) after culture with mitomycin C-treated mouse stimulator cells for 4--7 days. CML activity was detected in short term (4--6 h) isotope-release assays using 51Cr-labeled tumor cells or mitogen stimulated blast cells as targets. Rabbit CML effectors could distinguish between different mouse strains including congenics differing only at H-2. It was previously shown that rabbit CML precursors and effectors expressed antigens recognized by a specific anti-T cell serum (ATS). The current results demonstrate that T-enriched fractions from nylon wool columns were enriched for CTL precursors and were sufficient to generate CML responses. These data were most consistent with the xenogeneic CML being mediated by rabbit cytotoxic T-lymphocytes (CTL) analogous to murine CTL. Rabbit lymphocytes also produced a strong mixed lymphocyte (MLC) response when tested in microculture with mouse stimulator cells. However, optimal CML and MLC responses did not occur in lymphocytes from the same organ sources or subpopulation. These data implied that CML activity could be generated with little, if any, proliferation necessary.

An improved synthesis of 6-Methoxyanthranilic acid

6-Methoxyanthranilic acid (1) is prepared in three steps from 2,6- dinitrobenzoic acid (6) in an overall yield of 46%.

A comparative study of Jones's, Collins's and Corey's reagents in the chromium(VI) oxidation of an epimeric pair of allylic alcohols in the benzo-fused Norbornen-5-ol series

A comparison has been made between a series of chromium(VI) oxidizing agents, as well as manganese dioxide, a bicyclic allylic secondary alcohol, the exo-ol (7), being the substrate. Jones's, Collins's and Corey's reagents gave, in each case, a mixture of products: the main reactions were epoxidation to yield (8) and (9), normal ketone formation (10), and ring-fragmentation to form the indanol (11) and the indanone (12). All reagents yielded substantial amounts of epoxide, which is rare for Collins's reagent, and unprecedented for Corey's reagent, and varying amounts (13-30 %) of ketone, while Jones's reagent alone gave significant ring-opened products. A dramatic change in product composition was observed with the epimeric endo-alcohol (13), where Jones's reagent (only one studied) yielded the related α,β,-unsaturated ketone (10) in essentially quantitative yield. A discussion of these results is presented in terms of the current understanding of the mechanism of chromium oxidations.

The preparation and acid-catalysed rearrangement of a spiro epoxy alcohol in the benzo-fused norbornene series

Epoxidation of 3-(1?-methylethylidene)-1,2,3,4-tetrahydro-1,4- methanonaphthalen-exo-2-ol (1) with meta-chloroperbenzoic acid formed exclusively the exo-epoxide (2). Acid-catalysed rearrangement of this spiro epoxy alcohol yielded two ring-expanded keto alcohols, exo-8- hydroxy-6,6-dimethyl-6,7,8,9-tetrahydro-5,9-methano-5H- benzocyclohepten-7-one (24) and exo-8-hydroxy-7,7-dimethyl-6,7,8,9- tetrahydro-5,9-methano-5H-benzocyclohepten-6-one (21), with the former predominating. Chemical and spectroscopic (including l.i.s.) methods were used to determine the structure of (21) and (24).

An improved synthesis of 2-(1,1-Dimethylprop-2-enyl)indole

The condensation of aniline with 1-bromo-3,3-dimethylpent-4-en-2-one yields 2-(1,1-dimethylprop-2-enyl)indole.