The Electronic Structure of Dopamine. An ab initio Electrostatic Potential Study of the Catechol Moiety

Electronic properties of dopamine were studied by the ab initio STO-3G MO method. The molecular electrostatic potential (MEP) around the aromatic ring and the catechol group remains practically the same in 3,4-dihydroxytoluene (a model compound) and in neutral dopamine examined in its two extended conformations, namely that found in the crystal (side-chain and aromatic ring almost perpendicular) and the one corresponding to 2-amino-6,7-dihydroxytetralin (6,7-ADTN) (side-chain and aromatic ring almost coplanar). In protonated dopamine and in dopamine hydrochloride, the electrostatic potential of the catechol moiety is overshadowed by the positive charge, but the main features remain discernible. The catechol moiety was examined in its two coplanar conformations containing a ‘flip-flop H-bond’. The electrostatic potential around the catechol moiety is quite complex, with alternating positive and negative maxima. At increasing distances above and away from the catechol moiety, only two peripheral maxima, one negative and one positive, remain perceptible. The ‘flip-flop’ mechanism results in an approximate interchange of these two potential maxima, a fact which tends to level out the structural differences between the α- and β-rotamer of dopamine. Based on these results and on the structure of rigid agonists, some pharmacophoric features of dopamine agonists are proposed.     

Experimental and theoretical conformation analysis of eight-membered silocines with planar fragments

The dipole moments of 6-thia-4,5: 6,7-dibenzo-1,3,2-dioxasilocines were determined experimentally and calculated at the DFT B3LYP/6-31G* level of theory and by the additivity scheme. The experimental and theoretical (DFT B3LYP/6-31G*) conformation analysis of eight-membered 1,3,2-dioxasilocines having planar fragments showed that these compounds in solution exist as boat-chair, boat-boat, or twist-boat conformers, depending on the presence of unsaturated planar fragment, nature of the heteroatom in position 6 of the eight-membered ring, and substituents on the silicon atom.     

Synthesis of 7-hydroxy-6-alkoxy derivatives of 3,4-dihydroisoquinoline by ritter reaction

1-Substituted 6,7-dialkoxy-3,4-dihydroisoquinolines containing in the position 7 of the isoquinoline ring propoxy- or butoxy groups in the course of maintaining in the concentrated sulfuric acid are converted into 1-substituted 6-alkoxy-7-hydroxy-3,4-dihydroisoquinolines.     

1H and 13C NMR study of dihydro derivatives of methylphenobarbital

Sodium borohydride reduction of methylphenobarbital leads to the formation of two different dihydroderivatives, reduced either in position 4 or position 6. The structures of the derivatives have been determined through analysis of the ¹H and ¹³C NMR spectra of phenobarbital, methylphenobarbital and their derivatives. Detailed interpretation of the spectra and the resulting spectral parameters indicate conformations where the hydroxyl groups are axial and trans to the ethyl group. In these configurations the phenyl ring becomes equatorial. The results also allow an unambiguous assignment of the resonances of the phenyl carbons 2′(6′) and 3′(5′) of phenobarbital and the carbonyl carbons 4 and 6 of methylphenobarbital, differing interpretations having been previously advanced in the literature.     

New synthesis of 5,6,7,8-tetrahydro-4H-thieno[2,3-d]azepine

This paper describes two new access routes to 5,6,7,8-tetrahydro-4H-thieno[2,3-d]azepine from 2-(2-thienyl)ethylamine or its N-(2-chlorobenzyl) derivative. One of these two syntheses involves a new ring expansion from a 6,7-dihydro[3,2-c]pyridinium derivative, chloromethylated in position 4.     

Synthesis of two new heterocyclic ring systems: Benzo[3,4] cyclohepta[1,2-d]-pyrimidines and benzo[3,4]cyclohepta[2,1-d] pyrimidines

Three 2,4-diamino-l(), 11-dihydro-9H-benzo[3,4]cyclohepta[ 1,2-d]pyrimidines (6a-6c) representing the first examples of a new ring system were synthesized from 2-benzosuberones and cyanoguanidine. Similarly, 2,4-diamino-6,7-dihydro-5H-benzo[3,4]cyelohepta[2,1-d]pyrimidine ( 24 ) was prepared from 1-benzosuberone. The ultraviolet spectral properties of these compounds were examined with reference to those of the analogs in which the central ring is five- and six-mernbered.     

350 MHz 1H NMR spectra,dipole moments and preferred conformation of 8,9-epoxy-6,7-dihydro-5H-benzocyclohepten-5-ones

350 MHz ¹H NMR spectra and dipole moments showed that in the preferred conformation of 8,9-epoxy-6,7-dihydro-5H-benzocyclohepten-5-one and its 1,4-dimethoxy derivative the oxirane ring takes a pseudo-axial position.     

Some anomalous reactions of 4-quinolone-5-diazonium salts

Diazotisation of the 5-amino function in 6,7-alkoxy-l-ethyl-l,4-dihydro-4-oxoquinoline-3-carboxylic acids led to various products. Dediazoniation was always accompanied by fission of the 6-alkoxy substituent; 6,7-methylenedioxy groups gave formaldehyde which could form a m-dioxino ring. Hydrolysis of the diazonium chlorides resulted in halo-dediazoniation.     

Conformational preferences of 6-furfuryl amino purine and 6-benzyl amino purine

Conformational preferences of N⁶-furfurylamino purine (kinetin) and N⁶-benzyl amino purine (BAP ) have been investigated theoretically by the quantum chemical perturbative configuration interaction using localized orbitals method. The predicted most stable conformations for these molecules are quite similar. The N⁶ substituents in both these molecules are oriented toward N(1) and away from the imidazole moiety of the purine. The furfuryl ring in kinetin as well as the aromatic benzene ring in BAP are not coplanar with the purine ring. Comparison of these results with the preferred conformation of another compound N⁶-(Δ²-isopentenyl) adenine reveals striking similarity in the orientations of the N⁶ substituents in these cytokinin-active plant-growth-stimulating substances.     

5,5‐Dimethyl‐2,8‐diphenyl‐5H‐dibenzo[b,f]silepine: a synchrotron study

The molecule of the title silepine compound, C₂₈H₂₄Si, lies on a crystallographic general position but has almost exact mirror symmetry. The seven‐membered silepine ring has a boat conformation, with a fold angle of 99.99 (9)° between the C—C=C—C stern and the C—Si—C prow. The planes of the phenyl substituents are rotated by 32.23 (6) and 31.80 (7)° out of the planes of the respective fused benzene rings. Similar folded conformations are found for other dibenzo[b,f]silepines, while analogous dibenzo[b,f]borepines, in which the B atom can participate in conjugation, have a more flattened heterocyclic ring.     

Similar molecular constitutions but different conformations and different supramolecular assemblies in two related fused tetracyclic benzo[b]pyrimido[5,4‐f]azepine derivatives

A simple and effective two‐step approach to tricyclic pyrimidine‐fused benzazepines has been adapted to give the tetracyclic analogues. In (RS)‐8‐chloro‐6‐methyl‐1,2,6,7‐tetrahydropyrimido[5′,4′:6,7]azepino[3,2,1‐hi]indole, C₁₅H₁₄ClN₃, (I), the five‐membered ring adopts an envelope conformation, as does the reduced pyridine ring in (RS)‐9‐chloro‐7‐methyl‐2,3,7,8‐tetrahydro‐1H‐pyrimido[5′,4′:6,7]azepino[3,2,1‐ij]quinoline, C₁₆H₁₆ClN₃, (II). However, the seven‐membered rings in (I) and (II) adopt very different conformations, with the result that the methyl substituent occupies a quasi‐axial site in (I) but a quasi‐equatorial site in (II). The molecules of (I) are linked by C—H...N hydrogen bonds to form C(5) chains and inversion‐related pairs of chains are linked by a π–π stacking interaction. A combination of a C—H...π hydrogen bond and two C—Cl...π interactions links the molecules of (II) into complex sheets. Comparisons are made with some similar fused heterocyclic compounds.     

An Unexpected Pyrimidine Ring Transformations in the Reaction of 4‐aryl‐5‐nitro‐6‐bromomethylpyrimidin‐2(1H)‐ones with Anilines

The reaction of 4‐aryl‐6‐bromomethyl‐5‐nitro‐3,4‐dihydropyrimidin‐2(1H)‐ones, containing three possible combinations of substituted and unsubstituted nitrogen atoms with anilines depending on the conditions leads to the products of ring contraction of the pyrimidinone ring into an imidazolone, as well as to the formation of 7‐aryl‐6,7‐dihydroisoxazolo[4,3‐d]pyrimidin‐5(4H)‐one derivatives, and in some cases to the 5‐aminopyrimidinones. The mechanisms of these unusual ring transformations are discussed.     

Chemistry of 2H-3,1-benzoxazine-2,4(1H)-dione (isatoic anhydride). 16. Facile construction of the furacridone ring system

The synthesis of the furacridone ring skeleton was accomplished in one step by the reaction of N-methylisatoic anhydride ( 7 ) with the lithium enolate derived from 6,7-dihydro-4(5H)-benzofuranone ( 10 ). Aromatization of the C ring with DDQ furnished 5-dehydroxyfuracridone ( 6 ).     

2,3:4,6‐Di‐O‐isopropylidene‐α‐l‐sorbofuranose and 2,3‐O‐isopropylidene‐α‐l‐sorbofuranose

In the title compounds, C₁₂H₂₀O₆, (I), and C₉H₁₆O₆, (II), the five‐membered furanose ring adopts a ⁴T₃ conformation and the five‐membered 1,3‐dioxolane ring adopts an E₃ conformation. The six‐membered 1,3‐dioxane ring in (I) adopts an almost ideal ^OC₃ conformation. The hydrogen‐bonding patterns for these compounds differ substantially: (I) features just one intramolecular O—H...O hydrogen bond [O...O = 2.933 (3) Å], whereas (II) exhibits, apart from the corresponding intramolecular O—H...O hydrogen bond [O...O = 2.7638 (13) Å], two intermolecular bonds of this type [O...O = 2.7708 (13) and 2.7730 (12) Å]. This study illustrates both the similarity between the conformations of furanose, 1,3‐dioxolane and 1,3‐dioxane rings in analogous isopropylidene‐substituted carbohydrate structures and the only negligible influence of the presence of a 1,3‐dioxane ring on the conformations of furanose and 1,3‐dioxolane rings. In addition, in comparison with reported analogs, replacement of the –CH₂OH group at the C1‐furanose position by another group can considerably affect the conformation of the 1,3‐dioxolane ring.     

The synthesis of 6,7-dihydro-5H-pyrrolo[3,4-d]pyrimidines. II. 4-Hydroxy, 4-mercapto, 2-amino-4-hydroxy and 2,4-dihydroxy derivatives

Several new types of compounds in the 6,7-dihydro-5H-pyrrolo[3,4-d]pyrimidine series have been prepared. Included are a 6-acyl derivative unsubstituted in the pyrimidine ring, as well as 4-hydroxy, 4-mercapto, 2-amino-4-hydroxy and 2,4-dihydroxy derivatives. These products were derived directly or indirectly from 4-cyano- or 4-carbethoxy-1-acyl-3-amino-3-pyrroline intermediates. 3-Hydroxy, 3-amino, and 3-thioformylamino-1-acyl-3-pyrroline-4-thiocarboxamides have been obtained and the 3-thioformylamino derivatives shown to undergo base-catalyzed cyclization to close a 4-mercaptopyrimidine ring.     

Investigation of the products of the reaction of epichlorohydrin with aromatic amines

N-(-Chloro--hydroxy)propyl derivatives of 5-chloro-1-naphthylamine, 8-chloro-1-naphthylamine, and 5-cyano-1-naphthylamine were obtained. They were cyclized to 1,2,3,4-tetrahydro-3-hydroxy-7-chlorobenzo[f]quinoline (II), 1,2,3,4-tetrahydro-3-hydroxy-10-chlorobenzo-[fJquinoline (VII), and 1,2,3,4-tetrahydro-3-hydroxy-7-cyanobenzo[f]quinoline (X). Chlorination at the 6 position to form 1,2,3,4-tetrahydro-3-hydroxy-6,7-dichlorobenzo[f]quinoline occurs under the action of thionyl chloride on II at room temperature. The action of thionyl chloride on II, VII, and X at elevated temperatures leads not only to chlorination at the 6 position but also to aromatization of the tetrahydropyridine ring to form, respectively, 6,7-dichlorobenzo[f]quinoline (V), 6,10-dichlorobenzo[f]quinoline (VIII), and 6-chloro-7-cyanobenzo[f]quinoline (XIII).See [5] for Communication V.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1522–1525, November, 1970.     

Synthesis of Artificial Glycoconjugate Polymers Carrying 6-O-Phosphocholine α-D-Glucopyranoside,Biologically Active Segment of Main Cell Membrane Glycolipids of Mycoplasma Fermentas

ABSTRACT

The conformation of two mannose-based amidines, the N-benzylmannoamidine and a pseudo (1→6) dimannoside, has been evaluated using semi-empirical AMI calculations and ¹H NMR studies. The most stable conformations of the mannoamidine ring correspond to the half-chair forms ³H₄ and ⁴H₃. The conformations (Z) or (E) about the exocyclic C-N bond depend on the substituents and it was shown that, in solution, the N-benzylmannoamidine was (E)-configured whilst the pseudo (1→6) dimannoside was (Z)-configured. Using the grid-search approach, the potential energy maps of both mannoamidines were calculated as a function of the torsion angles which define the orientation of the amidine substituent. Three stable conformers were identified for the N-benzylmannoamidine and seven for the pseudo (1→6) dimannoside. Inter-glycosidic NOE have provided evidence for a preferred conformation of the pseudo (1→6) dimannoside in solution. The transition state structure of the α-phenylmannose hydrolysis was optimized using the AMI method and compared to the N-benzylmannoamidine. The developing oxocarbenium ion is well matched by the mannoamidine ring but the orientation of the phenyl group in the inhibitor differs significantly from the position of the leaving group in the transition state. The use of sugar type amidines as haptens to obtain catalytic antibodies is then discussed.

     

Sulfur-rich heterocycles from 2-metalated benzo[b]thiophene and benzo[b]furan: synthesis and structure

The reaction of 2-lithiated benzo[b]thiophene with 8 equiv of elemental sulfur was found to give pentathiepino[6,7-b]benzo[d]thiophene. In contrast, treatment of 2-lithiated benzo[b]furan with sulfur under similar conditions produced the interesting ring system bis(benzo[4,5]furo)[2,3-e:3',2'-g][1,2,3,4]tetrathiocine. Both of these new cyclic polysulfides were studied by X-ray crystallography. Two polymorphic forms of pentathiepino[6,7-b]benzo[d]thiophene were found, displaying similar conformations but different packing schemes, which was also evident from powder diffraction data.     

Novel hexahydrofuro[3,4-b]-2(1H)-pyridones from 4-aryl substituted 5-alkoxycarbonyl-6-methyl-3,4-dihydropyridones

The title compounds 6 have been prepared in a one-step procedure from the corresponding 4-aryl substituted 5-alkoxycarbonyl-6-methyl-3,4-dihydropyridones 4 in good yields. Quantum chemical calculations reveal a non-planar molecule with a distorted dihydropyridone ring and two favoured conformations. The 13C nmr data and theoretical calculations support a strong push-pull effect on the olefinic moiety.     

Methyl 4‐O‐benzoyl‐2,3‐O‐isopropyl­idene‐α‐l‐rhamnopyran­oside

The title compound, C₁₇H₂₂O₆, has an exocyclic ester group at the hexopyranosyl sugar residue. The carbonyl group shows a conformation that is eclipsed with respect to the adjacent ring C—H bond. The two ester torsion angles are denoted by syn and cis conformations. One of these torsion angles is indicated to have a similar conformation in solution, as analyzed by NMR spectroscopy and a Karplus‐type relationship.