Search

The affinity of L-DNAs, L-RNAs and L/D-DNAs for homopurine homopyrimidine d.s. D-DNA and s.s. D-RNA was probed by gel electrophoresis and CD spectroscopy. It was found that the L-modified oligomers do not bind to d.s. DNA and to natural RNA that contains all four natural bases. Thus they cannot be used, in general, for the control of gene expression according to the antigene and antisense methodologies. Heterochiral complexes with 1:1 stoichiometry and low thermal stability are formed, instead, by homopurinic L-RNA or L/D-DNA and homopyrimidinic L-RNA with the W/C complementary natural RNA sequences.

L-beta-Deoxythymidine (L-dT), the optical enantiomer of D-beta-deoxythymidine (D-dT), and L-enantiomers of nucleoside analogs, such as 5-iodo-2'-deoxy-L-uridine (L-IdU) and E-5-(2-bromovinyl)-2'-deoxy-L-uridine (L-BVdU), are not recognized in vitro by human cytosolic thymidine kinase (TK), but are phosphorylated by herpes simplex virus type 1 (HSV-1) TK and inhibit HSV-1 proliferation in infected cells. Here we report that: (i) L-dT is selectively phosphorylated in vivo to L-dTMP by HSV-1 TK and L-dTMP is further phosphorylated to the di- and triphosphate forms by non-stereospecific cellular kinases; (ii) L-dTTP not only inhibits HSV-1 DNA polymerase in vitro, but also human DNA polymerase alpha, gamma, delta and epsilon, human immunodeficiency virus reverse transcriptase (HIV-1 RT), Escherichia coli DNA polymerase 1 and calf thymus terminal transferase, although DNA polymerase beta was resistant; (iii) whereas DNA polymerase beta, gamma, delta and epsilon are unable to utilize L-dTTP as a substrate, the other DNA polymerases clearly incorporate at least one L-dTMP residue, with DNA polymerase alpha and HIV-1 RT able to further elongate the DNA chain by catalyzing the formation of the phosphodiester bond between the incorporated L-dTMP and an incoming L-dTTP; (iv) incorporated L-nucleotides at the 3'-OH terminus make DNA more resistant to 3'-->5' exonucleases. In conclusion, our results suggest a possible mechanism for the inhibition of viral proliferation by L-nucleosides.

Anthracycline antibiotics daunomycin and adriamycin are among the most widely used in cancer chemotherapy and DNA is believed to be the primary target of their biological action. The crystal structure of a morpholino derivative of adriamycin bound to the DNA hexamer d(CGTACG) has been determined at 1.5 A resolution. The complex crystallizes in space group P1 with unit cell dimensions a = 18.01 A, b = 18.83 A, c = 27.65 A, alpha = 92.6 degrees, beta = 100.5 degrees, gamma = 94.9 degrees and there are two drug molecules bound per duplex. Morpholino derivatives differ greatly from their parent compounds in their biological and pharmacological properties. Structural comparison of this complex with the series of previously reported anthracycline-DNA complexes offers an opportunity for studying relationships between structure and function. The anthracycline chromophore intercalates at the CpG step and DNA distortions from a B-type conformation are similar to those observed in the other DNA-anthracycline complexes. Interactions between drug and DNA show no differences at the intercalation site, while in the minor groove they are significantly affected by the presence of the bulky morpholinyl moiety on the anthracycline amino sugar. The binding site involves four base-pairs and the absence of a positive charge on the amino sugar appears to influence the hydration pattern on both grooves. The two halves of the duplex are symmetrically related by a non-crystallographic 2-fold axis but they are not equivalent. In one half, one magnesium cluster bridges both drug and DNA, further stabilizing the complex.

The hydroxybenzotriazole phosphotriester approach has been successfully applied to the PEG-supported synthesis ( HELP ) of oligodeoxynucleotides. Main advantages over the MSNT-based HELP procedure are the elimination of side-reactions at the guanosine level and the use of the 1ess expensive protected nucleosides as starting materials.

The hydroxybenzotriazole phosphotriester approach has been successfully applied to the PEG-supported synthesis ( HELP ) of oligodeoxynucleotides. Main advantages over the MSNT-based HELP procedure are the elimination of side-reactions at the guanosine level and the use of the 1ess expensive protected nucleosides as starting materials.

Using polyethylenglycol (PEG) as soluble supporting polymer, oligonucleotides have been prepared in high yield by an easy and fast procedure. The method looks promising for rapid synthesis of grams of short oligomers at reasonable cost.

A simple, rapid and high-yielding method for the synthesis of oligonucleotides by the phosphotriesters approach is described. The use of polyethylene glycol (PEG) as soluble polymeric support preserves some convenient features of the solid-phase synthesis with new interesting advantages. Short oligonucleotides in hundred milligrams scale can be obtained from few grams of functionalized PEG.

The effects of different DNA sequences on the photoreaction of various furocoumarin derivatives was investigated from a quantitative point of view using a number of self-complementary oligonucleotides. These contained 5'-TA and 5'-AT residues, having various flanking sequences. The furocoumarins included classical bifunctional derivatives, such as 8-methoxy- and 5-methoxypsoralen, as well as monofunctional compounds, such as angelicin and benzopsoralen. Taking into an account the thermodynamic constant for noncovalent binding of each psoralen to each DNA sequence, the rate constants for the photobinding process to each fragment were evaluated. The extent of photoreaction is greatly affected by the DNA sequence examined. While sequences of the type 5'-(GTAC)n are quite reactive towards all furocoumarins, 5'-TATA exhibited a reduced rate of photobinding using monofunctional psoralens. In addition terminal 5'-TA groups were the least reactive with 5- and 8-methoxypsoralen, but not with angelicin or benzopsoralen. Also 5'-AT-containing fragments exhibited remarkably variable responses toward monofunctional or bifunctional psoralen derivatives. As a general trend the photoreactivity rate of the former is less sequence-sensitive, the ratio between maximum and minimum being less than 2 for the examined fragments. The same ratio is about 3.4 for 8-methoxypsoralen and 6.2 for 5-methoxypsoralen. This approach, in combination with footprinting studies, appears to be quite useful for a quantitative investigation of the process of covalent binding of psoralens to specific sites in DNA.

The binding between Distamycin 3 and the palindromic duplexes d(CGTTTAAACG)2 and d(CGTACGTACG)2 was investigated by two independent techniques: UV-Vis absorption in the Job's plot approach and Induced Circular Dichroism. Both decamers bind two molecules of peptide per duplex, with close overall affinities. This result indicates that a row of six A:T base pairs can accommodate two molecules of drug and that the minimal binding site of Distamycin 3 can consist of just two A:T base pairs.

Unnatural L-2'-deoxyribonucleosides L-T, L-dC, L-dA and L-dG were prepared from L-arabinose and assembled, by solution or solid phase synthesis, to give L-oligonucleotides (L-DNAs), which contain all four natural bases. The affinity of these modified oligomers for complementary D-ribo- and D-deoxyribo-oligomers was studied with NMR, UV and CD spectroscopies and mobility shift assay on native PAGE. All experimental results indicate that L-DNAs do not, in general, recognize single-stranded, natural DNA and RNA. Hence, contrary to previous suggestions, it is not possible to envisage their use as wide scope antimessenger agents in the selective control of gene expression.

The radical adducts resulting from the reaction between group IVB organometallic radicals MR 3 (M = Si, Ge, Sn; R = alkyl or aryl) and a number of thioketones of the chromone and flavone series have been investigated by ESR spectroscopy. The spectral parameters obtained for these species have been compared with those of similar adducts of the corresponding ketones. Both classes of radicals adopt an orthogonal conformation, and the differences between the former and the latter paramagnetic species can be accounted for by the different electronegativity of oxygen and sulphur. the effects of substitution of the heterocyclic oxygen with a sulphur or selenium atom on the spin density distribution are likewise explained. INDO calculations have been carried out on the model systems CH 2 XSiH 3 (X = O, S).

The 15N and 13C chemical shifts of the sodium salt of deoxycytidylyl-(3′,5′)-guanosine have been measured in dimethylsulfoxide in the presence of variable amounts of CF3COOH. N3(cyt) is protonated first, followed by N7(gua) and the phosphate anion. These results vary from those reported for the binding of the methylmercuric cation to d(CpG).

The electron transmission spectra of the o,o ′-dimethyl substituted benzenes 2,6-(CH 3 ) 2 C 6 H 3 -XR (X = O,S, NR: R = H, CH 3 ) show that the substituents adopt a planar (R = H) or rotated (R = CH 3 ) conformation depending upon their size and they suggest that in the sulphur derivatives the 2 B 1 H anion states are stabilized by S3d orbital participation. MS Xα calculations performed on both the planar and orthogonal forms of the model systems p -(XH) 2 -C 6 H 4 (X = O, S) support this hypothesis and assign the extra resonance present in the ET spectra of the thio derivatives to electron capture into [ σ S-R * MOS. strongly mixed with sulphur 3d orbitals ( = 33% d character).

The shake-up satellites present in the O 1s and N 1s energy regions of the XPS spectra of the planar 4-N-piperidyl-nitrobenzene ( 1 ) and 2-N-piperidyl-5-nitrothiophen ( 3 ), and of the sterically hindered 2-N-piperidyl-nitrobenzene ( 2 ), 2-N-piperidyl-3-nitrothiophen ( 4 ) and 3-N-piperidyl-2-nitrothiophen ( 5 ) and, for comparison, of 2-bromo-3-nitrothiophen ( 6 ) have been analyzed with the help of CNDO/S CI calculations. The spectra of the planar derivatives closely resemble these of the related compounds previously analysed, the main satellites deriving from the transition between the highest occupied molecular orbital (HOMO, localized at the donor-ring moiety) towards the lowest unoccupied one (LUMO, localized at the nitro group). Calculations indicate that in the ortho derivatives new relaxation processes are allowed upon N 1s /NO 2 ionization. In 2 , where the angle of rotation θ is closer to 90° than 60°, the NR 2 lone-pair orbital relaxes through space towards the core-ionized N/NO 2 atom. In 4 and 5 , where 45° ⩽ θ ⩽ 60°, both through-ring and through-space relaxations are present. The assignment of the main N 1s /NO 2 line in 1 is discussed.

2D 31P/1H correlation spectroscopy has been used to assign individual phosphates in the self-complementary DNA fragment d(CGTACG), which is present in solution as a B-DNA type double helix. 31P chemical shift variation with temperature and with the base sequence has been studied, and evidence is given of a steric clash between purines in the minor groove, affecting the chemical shift of the innermost TpA phosphate. For this hexanucleotide there is a good correlation of 31P shifts with both the helical twist (∑1) and roll angle (∑2) Calladine-Dickerson sum functions. Different types of linear correlations, also including data from other nuclotides, have been performed. The results show that it is more appropriate to consider the change in chemical shifts as it occurs during melting rather than the actual 31P shifts. An interesting correlation was also found between 31P chemical shifts and P,H-3′ coupling constants.

The ESR spectra of the paramagnetic species produced by photoreaction of benzo[2,1-b;3,4-b]dithiophen-4,5-dione with a number of organomercurials, RHgR, have been recorded. The spectral parameters and the temperature dependence of the 199Hg coupling constants are consistent with a structure of the adducts in which the Hg atom is bound to both carbonyl oxygens.

The photoelectron (He(I)) spectra of the tricyclic tetracarbonyl compounds pyromellitic dianhydride, dithioanhydride and diimide and of the tetracyclic hexacarbonyl compound trimellitic anhydride have been investigated. To aid the interpretation of the main features of the spectra, i.e. the ordering and splitting of the nCO ionisations and the behaviour of the ‘benzenic’ and heteroatom π ionisations, MO calculations based on a ZDO pragmatic model and semiempirical SCF-PP calculations have been carried out. The evolution of the nCO and πX ionisations upon progressive fusion of anhydride moieties with a benzene nucleus is analysed in detail. The proposed orbital sequences for the n orbitals are: ag(S+) $ b1u(AS+) $ b2u(S−) $ b3g(AS−) for the tetracarbonyls and a′1(S+) $ e′(AS+) $ a′2 (AS−) ≈ e′(S−) for the hexacarbonyl.

The photoelectron (He(I)) spectra of 1,2-indandione and heteroanalogues (coumarandione, thionaphthenequinone, and isatin), 1,3-indandione and heteroana

The first two ionization energy values of p-substituted trans-azobenzenes pX-C6H4-N = N-C6H5 (X = NH2, OCH3, OH, CH3, H, Cl, COOH and NO2) are reported. These have been obtained by U.V. (HeI and HeII) photoelectron spectroscopy (UPS). The substituent effect indicates that for electron donor substituents, the highest occupied orbital is π-type. This is confirmed by semiempirical calculations. When the substituent is H or a withdrawing group, the first two bands heavily overlap, and in these cases no certain assignment was possible, in spite of the several approaches used. The UPS data are discussed along with previous polarographic and U.V. absorption measurements.

The sodium salt of the dinucleoside phosphate d(GpG), dissolved in water, forms two mesophases which have been characterized, by optical microscopy, as being of the cholesteric (columnar chiral nematic, N∗) and hexagonal (M) type.

The u.v. photoelectron spectra of a number of push-pull substituted ethylenes with two donor groups and with planar or twisted double bonds have been interpreted by the aid of perturbational arguments, CNDO/2 calculations, and comparison with published spectra of similar compounds. The highest bonding molecular orbital in all cases is of π-type, and its energy is raised with increasing twist about the double bond, whereas the orbital formed by anti-symmetric combination of the donor atom pz orbitals is unchanged or lowered by increased twist. Through-bond interaction splits the ‘non-bonding’ oxygen orbitals by 0.6–0.7 eV in 1,1-diacetyl-2,2-diaminoethylenes, in which the carbonyl groups are E,Z oriented with respect to the CC double bond. When Z,Z orientation is enforced by ring closure, the splitting is only 0.38 eV, in agreement with calculations. In the 2,2-dithio-analogues, interaction with the C–S bond orbitals leads to a more complex splitting pattern.

The photoelectron He(I) and He(II) spectra of 4H-pyran-4-one ( 1 ), 4H-thiopyran-4-one ( 2 ), 4H-pyran-4-thione ( 3 ) and 4H-thiopyran-4-thione ( 4 ) are reported. The assignments are based on experimental evidence, taking into account the results of theoretical calculations. The outermost orbital sequences proposed (X = O, S) are n X (σ), 3 b 1 (π), 1 a 2 (π) for 1 , 2 and 4 ; and 3 b 1 (π), n X (σ) and 1 a 2 (π) for 3 . The shifts of the core-ionization energy values for 1–4 are ascribed to a drift of π-charge from the intracyclic heteroatom towards the carbonyl or thiocarbonyl group. Low-energy shake-up satellites (up to 25% with respect to the main line) are observed in the various energy regions of the XPS spectra. They are qualitatively reproduced by CNDO/2 calculations. The most important satellites derive from the transition in the ion corresponding to the 3 b 1 (π) → 4 b 1 (π*) transition in the UV-visible spectra of the neutral molecules. Charge rearrangements accompanying this transition lead to charge depletion of the core-ionized atom.

The ultraviolet photoelectron spectra of [2,2](2,5)furanophane (FUPH) and [2,2](2,5)thiophenophane (THPH) have been analyzed on the basis of a perturbational molecular orbital analysis, by comparison with CNDO/2 computations and by correlating them with the spectra of related molecules. Through space and through bond interactions between the two heteroaromatic rings are shown to be important in determining the ordering of the outermost MO’s in this class of compounds.

The photoelectron (HeI) spectra of 1,3-thiazole and its 2F, 2Cl, 2Br, 4Br and 5Br-derivatives are reported. The assignment of the first few bands of the various spectra to the corresponding molecular orbital is based, for thiazole, on the results of an ab initio SCF—MO calculation, while for the various halogen derivatives, on reasonings based on perturbation theory. In particular, the first five outermost molecular orbitals of thiazole probably correspond to π3 (9.50 eV), π2 (10.24), σN (10.48; orbital mainly localized on the nitrogen atom), σS (12.78; orbital mainly localized on the sulphur atom) and π1 (13.5).

The intensity of the shake-up satellites present in the solid-phase XPS spectra of paranitroaniline ( 1 ), 2-amino-5-nitropyridine ( 2 ) and 2-amino-5-nitropyrimidine ( 3 ) decreases from ( 1 ) to ( 3 ) in agreement with CNDO/S CI calculations. The HOMO—LUMO energy gap appears to be responsible for the observed trend.

The ET spectra of monosubstituted benzenes containing the −OH, −OCH 3 , −OC(CH 3 ) 3 , −SH, −SCH 3 , −SC(CH 3 ) 3 and −NHCH 3 groups show that in the non-hindered nitrogen and oxygen derivatives the lone pair/π* interaction produces a significant destabilization of the ring 4b 1 π* MO, while the electron affinity (EA) of the LUMO π* 2a 2 is close to that of benzene. The stabilization of the empty π* MOs produced by the sulphur-containing substituents demonstrates the presence of interacting empty orbitals localized at the substituent. The stabilizing effect of these orbitals does not change significantly with the σ framework of the substituent nor with its torsional angle around the S-ring bond. This is consistent with the S 3d character of the stabilizing orbitals. The EA increase of the LUMO in the rotated −SC(CH 3 ) 3 derivative is mainly ascribed to the reduced interaction between the S lone-pair orbital and the 4b 1 π* MO, and, in part, to σ*/π* interaction.

The photoelectron (He(I)) spectra of 1,4-dithiin (1), 1,4-thiaselenin (2), 1,4-thiatellurin (3) and 4H-thiopyran (4) were assigned by comparison with published spectra of similar compounds and with the help of ab initio and semi-empirical calculations. The proposed orbital sequences for the outermost orbitals are π4, π3, π2, σ for 1, 2 and 3, and π4, π2, σ, π3 for 4. π4 and π3 correspond to the symmetric and antisymmetric combinations, respectively, of the heteroatom lone pairs, while π2 is the antisymmetric combination of the πeth orbitals.

The equilibrium and kinetic aspects of the interaction between four anthracyclines and two synthetic self-complementary hexanucleotides was investigated by fluorescence detection. Two of the studied anthracyclines are widely used antitumor drugs: doxorubicin (1, formerly adriamycin) and daunorubicin (2, formerly daunomycin). The other two, 9-deoxydoxorubicin (3) and 3'-deamino-3'-hydroxy-4'-epidoxorubicin (4), are doxorubicin analogues with modifications of the chemical groups that have been proposed as responsible for sequence specificity (Chen, K.-X., Gresh, N. and Pullman, B. (1985). J. Biomol. Struct. Dyn. 3, 445-466). One of the oligonucleotides, d(CGTACG), is identical to that used in the high resolution x-ray structure determination of the daunorubicin intercalative complex (Wang, A. H.-J., Ughetto, G., Quigley, G. J. & Rich, A. (1987). Biochemistry 26, 1152-1163). Binding to this hexanucleotide is compared with intercalation into the d(CGCGCG) duplex, revealing sequence preferences of the four anthracyclines. Taking into account the anthracycline aggregation and the dissociation of the hexanucleotide double standard form, results can be interpreted with a model that assumes complete fluorescence quenching at intercalative sites containing the CG base pair, and a large residual fluorescence after intercalation within the TpA fragment. All four anthracyclines show preferential intercalation at sites near the ends of both hexanucleotide duplexes, partly as a result of positive cooperativity in the formation of di-intercalated species at these sites. Within the limits of experimental error, complete site specificity for the CpG fragment is found in the intercalation of 1 and 2 into d(CGTACG) duplex, whereas analogues 3 and 4 give increasing evidence of intercalation at other sites including the fluorescence-preserving TpA fragment. Site specificity is less pronounced in the association with d(CGCGCG), when cooperativity is taken into account. Kinetic data corroborate the results of equilibrium studies and are interpreted with a mechanism that includes formation of an intermediate bound species followed by drug redistribution to preferential sites. Finally, from a comparison of pertinent site binding constants, approximate free energy contributions to sequence specific DNA interaction, due to C9-OH on the aglycone and -NH3+ on daunosamine, are estimated not to exceed 2 kcal/mol.

The photoelectron spectra of the S[X(CH3)3]2 and CH3SX(CH3)3 series (X = C, Si, Ge, Sn and Pb) are reported, and assigned on the basis of the semilocalized orbitals approximation and a consideration of symmetry and substituent effects. The electronic interactions between the X(CH3)3 substituents and the sulfur nπ orbital are discussed in terms of the relative importance of hyperconjugation (nσ mixing), (pd)π bonding and electrostatic interactions.

The analysis of dipole moment data obtained for dibenzo-p-dioxin, phenoxathiin, phenoxaselenin and phenoxatellurin in benzene at 25°C in conjunction with EHT calculations of the ocnformational energies show that these molecules adopt a non-planar conformation in solution. Each of the phenoxachalcogenins is folded along the axis connecting the two heteroatoms. A butterfly flapping motion about the planar conformation canot be excluded. The uv and photoelectron spectroscopic data support the conclusions drawn from the dipole moment studies. The spectroscopic data were interpreted with the help of SCF-PPP-CI calculations.

Vertical ionization energies of the two highest molecular orbitals and of orbitals mainly localized on the substituent of 31 α-substituted derivatives of furan, thiophen, selenophen, and tellurophen are discussed. The substituent effects confirm the reversal in the energy sequence of the two highest occupied π-MOs of tellurophen with respect to other five-membered heteroaromatic congeners and permit the assignment of the ionization energy values of the and π2, π3 MOs in selenophen. Assignments for some of the bands other than the first two it :he photoelectron spectra of tellurophen and selenophen are proposed. The effect of the ring on the orbitals mainly localized on the substituent is briefly discussed.

The first two π(a2, b1) IE’s, of monosubstituted benzenes containing di- and tri-coordinated nitrogen directly linked to the ring have been measured and analysed together with the N1s IE. These photoelectron properties are found to respond in the same sense, though to different extents, to inductive and mesomeric interactions that the N-containing substituents sustain with the aromatic ring. The different sensitivities of these properties to substituent changes are discussed in connection with mechanisms of transmission of electronic effects with the aid of the ground state electronic structures determined by means of ab-initio calculations. The relative contribution of the relaxation energy to the considered core and valence IE’s is also examined by referring to the model used by Gelius and Siegbahn. The factors determining the apparently anomalous behaviour of nitrobenzene are discussed

The low ionization energy regions of the photoelectron (He I) spectra of several p-p′-substituted thiobenzophenones (X-C6H4)2CS and of the corresponding S-oxides (sulphines) (XC6H4)2CSO (where X = H , OCH3, CH3, I, Br, Cl and NO2) have been assigned on the basis of perturbational molecular orbital theory arguments coupled with CNDO/2 computations and substituent effects. For the thioketones, the ordering of the outermost MO's results to be n(S), π7, π6, π5/π4, π3, n(S) being the HOMO; while for the sulphines the two outermost MO’s have π character and correspond to π7 and π6 in the thioketones. In the light of the above results the different behaviour toward oxidation of these two classes of compounds can be rationalized.

A rapid equilibrium is present in enaminic systems derived from 3-substituted cyclohexanones. Their reactions with β-nitrostyrene have been studied and the stereochemical implications discussed.

Morpholine, piperidine and pyrrolidine enamines of 2-methylcyclohexanone react with ethyl azodicarboxylate to give, after hydrolysis, 2-methyl-6-(N,N′-dicarbethoxy)hydrazinocyclohexanone in 49%, 47% and 84%, yield, respectively. The same enamines by reaction with phenyl isocyanate and subsequent hydrolysis furnish 2-methyl-6-phenylcarbamylcyclohexanone in 51%, 42% and 88% yield, respectively. These results reflect the percentages of the less substituted isomeric enamines and are in good agreement with those determined by NMR spectroscopy, 1-N-Morpholino-, 1-N-piperidino- and 1-N-pyrrolidino-2-(N,N′-dicarbethoxy)hydrazinocyclohex-1-en by kinetically controlled acidic hydrolysis, lead to the 2,6-disubstituted cyclohexanone having trans configuration, as results from NMR analysis and equilibration into the more stable cis isomer. The stereochemistry of such a reaction is reported and discussed.

The spin adducts of triphenylsilyl, triphenylgermyl and triphenylstannyl radicals with γ-pyrone, γ-thiopyrone, thia-γ-pyrone and thia-γ-thiopyrone have been studied by ESR spectroscopy. The spectral parameters indicate that these radicals adopt the conformation where the O-M or S-M bonds are eclipsed with the 2 p z orbital of the γ-carbon, despite the absence of hindering substituent groups in proximity of the radical centre. The electronic effects of sulphur and oxygen on the spin density distribution are also discussed.

The UV photoelectron spectrum of [2,2] metacyclo-2,6-pyridinophane has been analyzed on the basis of a perturbational molecular orbital analysis and CNDO/2 calculations. Through space and through bond interactions are shown to be present between the two pyridine rings. In particular a strong interaction has been found between the nitrogen lone pairs and the π systems of the rings.

The analysis of the photoelectron HeI spectra of the compounds Hg(SR) 2 (R = Me, Et, Pr n , Pr i , Bu n , Bu i and Bu t ) and of the results of iterative extended Huckel calculations on selected members of the series suggests that in these compounds the HgS bonds have a partial double-bond character due to a weak π-interaction between the filled 3 p sulphur orbitals and the emply 6 p orbitals of mercury.

The electron transmission spectra of 4H-thiopyran-4-one. 4H-pyran-4-thione and 4H-thiopyran-4-thione have been recorded in the 0–6 eV energy range and the observed resonances assigned to the corresponding anion states. Unlike γ-pyrone, its sulphur derivatives possess low-energy Σ anion states.

The ionization energy (i.e.) values for electrons in the π MOs of some tertiary amines and enemines derived from morpholine, piperidine and pyrrolidine have been determined by u.v. photoelectron spectroscopy. The effects of structural changes are discussed. The nitrogen lone pair i.e. value is taken as a measure of basicity of amines and enamines in the gas phase. The relative order of basicity is secondary amines < tertiary amines < enamines. This order differs from that found in aqueous solution probably because of solvation effects in the latter.

Polyfunctionalized aromatic urethanes and heterocyclic compounds are obtained from hydrazinosubstituted enaminoketones.

Die AS-Enamine (I) lassen sich mit β-Nitro-styrol (II) stereospezifisch zu den Produkten (III) umsetzen, deren Hydrolyse die cis-erythro-Ketone (IV) ergibt.