Stereoselective approach to uncommon tripeptides incorporating a 2,6-diaminopimelic acid framework: X-ray analysis and conformational studies. Part 4

Stereoselective synthesis of pseudopeptides 4, 5, 8, 9, 13 and 14, incorporating 2,6-diamino-4-methylen-1,7-heptanedioic acid residue, has been accomplished starting from the l-valine derived chiral synthon 1. The absolute configuration of new stereocentres was assigned on the basis of ¹H NMR spectra. The geometry of these unnatural tripeptides was deduced on the basis of ¹H NMR parameters and IR spectra. X-ray analysis of the unusual peptide 18 and conformational studies of 5, 9 and 14 are also reported.     

Stereocontrolled synthesis of enantiomerically pure unsaturated analogues of 2,6-DAP. Part 5

An efficient new stereocontrolled synthesis of (2R,6R)-(+)- and (2S,6S)-(−)-2,6-diamino-4-methylene-1,7-heptanedioic acid 8a and 9a, respectively, has been accomplished starting from the glycine-derived chiral synthon 1. The enantiomerically pure α-alkyl derivatives 8b–d and 9b–d have also been synthesized. The absolute configuration of the new stereocenters was assigned on the basis of ¹H NMR spectra.     

Titanium complexes containing new dianionic tetradentate [ONNO]-type ligands with benzyl substituents on bridging nitrogen atoms: Syntheses, X-ray structures, and catalytic activities in ring opening polymerization of lactide

Several titanium isopropoxides 1–8 have been prepared by the reaction of Ti(O-i-Pr)₄ with a series of corresponding tetradentate Salan-type [ONNO] ligands with benzyl or methyl substituents on bridging nitrogen atoms. They have been characterized by ¹H NMR, ¹³C{¹H} NMR, and elemental analysis. Solid state structures of compounds 2, 4, 6, and 7 have been determined by X-ray crystallography. X-ray diffraction analysis and ¹H NMR confirmed that these titanium complexes were all monomeric species with a six-coordinated central titanium in their solid and solution structures. Complexes 2, 4, 6, and 8 with benzyl substituents on bridging nitrogens gave PLA with higher molecular weight than compounds 1, 3, 5, and 7 with methyl substituents did.     

Stereocontrolled synthesis of unnatural cyclic dipeptides containing an l-valine unit

Stereoselective synthesis of unusual nonproteinogenic dipeptides 7a,b,d,e and h and 13b and i, containing an l-valine unit and a cyclic unnatural α-amino acid, has been accomplished starting from the l-valine derived chiral synthon 1. The absolute configurations of the new stereocentres were assigned on the basis of ¹H NMR spectra.     

A new stereoselective synthesis of sterically constrained uncommon α,α′-dialkylated α-amino acids. Part 2

The alkylation of the diastereomeric mixture of the chiral morpholinone derivatives 5 and 6 occurs with good yield and a prevalence of the cis isomer. Cleavage of the alkylated intermediates 7b,c yields enantiomerically pure sterically constrained uncommon α,α′-dialkylated α-amino acids. The absolute configuration of the new stereocentres has been assigned on the basis of the ¹H NMR spectra and NOE measurements. A model to explain the observed diastereoselection is proposed.     

Synthesis,structure and NMR spectroscopy of some rhodium(III) cyclometallated Schiff's base complexes derived from 2-benzylidene-3-methylpyridines. Crystal structure of [RhHI{2-(3-nitrobenzylidene)-3-methylpyridine}; (PPh3)2]

The Schiff's base derived from 2-amino, 3-methylpyridine and an aryl aldehyde reacts with either RhCI(PPh₃)₃ or [Rh(μ-C1)(cyclooctene)₂]₂ in the presence of four equivalents of L (L = PPh₃, P(4-C1C₆H₄)₃, P(cyclohexyl)₃, AsPh₃, SbPh₃) to give a Rh^III cyclometallated complex (2), in which the imine CH bond has oxidatively added to the metal. The complexes 2 react with reagents such as Br^-, CN^-, CH₃I, CNR (R = cyclohexyl, t-butyl), P(OCH₃)₃, CO, to give substitution products (3), in which the Cl has been replaced. The complexes 2 and 3, as well as some few Ir^III analogs (4), have been isolated and characterized using ¹H, ³¹P, and (occasionally) ¹³C NMR spectroscopy. The crystal structure of the complex RhHI{2-(3-nitrobenzylidene)-3-methylpyridine} (PPh₃)₂ (3b) has been determined by X-ray diffraction. The complex shows a distorted octahedral structure with the following bond distances (Å) and angles (°): Rh-I, 2.771(2); Rh-N(1), 2.15(1); Rh-C(7′), 1.98(2); Rh-P(1), 2.326(5); Rh-P(2) 2.332(5); P-Rh-P, 159.7(2), N(1)-Rh-C(7′), 78.5(6). In the light of the NMR and X-ray data, it is suggested that the C(R)N moiety exerts a large trans influence.     

Proton NMR criteria for configurational assignment of S-methylthianium cations

Certain ¹H NMR features are reported for several conformationally biased diastereomeric pairs of 6-membered methylsulphonium cations (4–7) the members of each pair differing for the axial or equatorial orientation of the S⁺CH₃ group. The configurational assignment being secured by ¹³C NMR, the scope of a number of ¹H NMR parameters is discussed as criteria for configurational and conformational analysis. Two mobile systems have also been considered, 2 and 9, whose ¹H NMR is consistent with their (independently determined) conformer distribution.     

Interaction entre groupes aromatique et polaire voisins—III: Synthese et etudes physico-chimiques d'acides p-x-phenyl-3 bicyclo[2.2.1] heptene-5 carboxyliques-2 et de leurs esters methyliques

The synthesis, ¹H and ¹³C NMR spectra of acids 1 to 4 and methyl esters 5 to 8 are described. Interaction of aromatic and polar groups in the cis acids must be steric in origin and not due to charge transfer complex or hydrogen bonding. The structure of 1e,3a,5e and 7e has been determined by X-Ray crystallography. ¹H and ¹³C NMR studies indicate that, in the cis compounds, the proximity of aromatic and polar groups tend to impose to them some largely predominant conformations which should be analogous in the crystal or in solution.     

Synthesis and properties of all members of methylated tropylium ions

An members of the methylated tropylium perchlorates have been synthesized and their properties (UV absorptions, ¹H NMR spectra, and charge-transfer spectra with pyrene) determined. The methylated tropylium ions other than the hexa- and hepta-methyl homologues have been prepared by abstracting a hydride ion with trityl perchlorate from the corresponding methylated tropilidenes. The preparation of the hexa- and hepta-methyltropylium ions has been effected by utilizing phosphorus pentachloride as the hydride-abstraction reagent. The methylated tropilidenes have been prepared via one of the three known routes, i.e. the ring expansion of methylated benzenes with diazomethane (Route 1) or with ethyl diazoacetate (Route 2), and the cycloaddition of cyclopropene or methylcyclopropenes with methylated thiophene 1,1-dioxides accompanied with the exclusion of sulfur dioxide (Route 3). The methyl ¹H NMR chemical-shift values have been assigned, partly with the aid of the Me ¹³C NMR chemical-shift data for the tropylium ions containing the Me groups on contiguous ring-carbons (3a, 4a, 5a, 6 and 7). The transition energy for the charge-transfer band of the tropylium ions with pyrene increases with the increase in the number of the Me group, indicating that the more methylated the tropylium ion, the more stable is the ion.     

Synthesis and characterization of new cyclotriphosphazene compounds

In the present study, spiro (1a), dispiro (1b, 2, 3), per-substituted spermine-bridged (6–9) and dispiroansa spermine (10) derivatives of cyclotriphosphazene have been synthesized. The structures of the novel compounds (1b, 6–10) have been characterized by elemental analysis, FTIR, mass spectrometry, ¹H and ³¹P NMR spectroscopy. The molecular structures of 1b, 2, 8, and 10 were determined by single crystal X-ray crystallography. In order to investigate the anti-tumour properties of the newly synthesized cyclotriphosphazene derivatives, in vitro cytotoxic activity test (MTT assay) has been performed using HT-29 (human colon adenocarcinoma) and Hep2 (human epidermoid larynx carcinoma) cell lines. The result of the MTT assay showed that while compound 1a has cytotoxic effect on both Hep2 and HT-29 cell lines, compound 3 has only cytotoxic effect towards the Hep 2 cells.     

Thiazo rifamycins—I : Structure and synthesis of rifamycins p,q and verde,novel metabolites from mutants of nocardia mediterranea

Structures 1, 2 and 3 have been assigned to rifamycins P, Q and Verde, novel metabolites isolated from a mutant strain of Nocardia mediterranea both on the basis of spectroscopic evidence (UV, IR, MS, ¹H and ¹³C NMR) in comparison with the model compounds rifamycin S (4), rifampicin (5) and 4-dimethylamino-4-deoxy-rifamycin SV (6), and of an unambiguous synthesis from rifamycin S (4).     

Synthesis,characterization and in vitro antimicrobial screening of quinoline nucleus containing 1,3,4-oxadiazole and 2-azetidinone derivatives

A series of 3-chloro-1-(aryl)-4-(2-(2-chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-ethyl-azetidin-2-ones (V)_1–12 have been synthesized and characterized by IR, ¹H NMR, ¹³C NMR and mass spectra. Synthesized compounds were screened for their antibacterial activity against four different strains like Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus pyogenes, while antifungal activity was determined against three different strains like Candida albicans, Aspergillus niger and Aspergillus clavatus. On the basis of statistical analysis, it has been observed that compounds gave significant co-relation.     

Synthesis of 5-substituted-3-phenacyloxime-1,2,4-oxadiazoles from acetylated or benzoylated benzoylthiacetamide with hydroxylamine hydrochloride : Spectral evidence for a tetrahedral carbinolamine intermediate

Acetylated and benzoylated benzoylthiacetamide 1a,b reacts with hydroxylamine hydrochloride in refluxing ethanol to yield 3 - acetylamino - and 3 - benzoylamino - 5 - phenyl - isoxazoles 2a,b, while 3 -phenacyloxime - 5 - substituted - 1, 4a,b are formed in the presence of sodium acetate or in pyridine.When refluxed in ethanol containing small amounts of concentrated hydrochloric acid, the above 1,2,4-oxadiazoles 4a, b rearrange to the corresponding isoxazoles 2a, b.The reaction in pyridine has been studied at 35° by using ¹H and ¹³C NMR spectroscopy. It has been possible to detect an adduct between the carbinolamine intermediate, resulting from the addition of hydroxylamine to the keto carbonyl group, and the starting thiamide.     

A new stereoselective approach to β-hydroxy-α-aminoacids and dipeptides

The chiral synthons 1, 2 and 1′ were submitted to aldol condensation to achieve both β-hydroxy-α-aminoacids and dipeptides. The configuration of the new stereogenic centers was assigned on the basis of ¹H NMR spectroscopic data.     

Synthesis and characterization of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide: X-ray structure of 4-methoxy-3-(sulfanylmethyl)- and 4-chloro-3-(selenenylbenzyl)-N,N-diisopropylpyridine-2-carboxamide

Synthesis of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide (1a and 1b respectively) has been reported. 1a and 1b were lithiated with 2 equiv. of n-BuLi or LDA at ?78 °C. Addition of elemental sulfur or selenium to the carbanion led to the formation of corresponding thiolate or selenolate anions respectively. The selenolate anions were aerial oxidized to afford the corresponding diselenides. The thiolate/selenolate anions were quenched with a variety of electrophiles to give unsymmetrical thio/selenoalkanes in moderate to good yields. Reductive cleavage of Se–Se bond has also been studied. The synthesized compounds were characterized by elemental analysis, NMR (¹H, ¹³C and ⁷⁷Se), FT-IR and mass spectral techniques. Crystal structures of two compounds, 6b and 7a, were determined by single crystal X-ray crystallography. Their crystal structure exhibits 1,4-type S?OCH₃ and Se?Cl intramolecular secondary interactions respectively. The relative thermal stability of 3a, 3b and 4a has also been established by thermogravimetric analysis.     

N-[2-(1H-吲哚-3)乙基]-2-乙酰噻唑-4-甲酰胺及其类似物的合成

N-[2-(1H-吲哚-3)乙基]-2-乙酰噻唑-4-甲酰胺是最近从海洋细菌中分离得到的一种新型的天然杀藻剂, 以D-丙氨酸为原料合成了该化合物, 并用类似的方法首次合成了它的类似物2, 3和4. 其关键步骤为通过将取代的4-噻唑甲酸制成混酐与色胺连接的偶联反应. 各中间体都通过¹H NMR和¹³C NMR得到证实. 最终产品通过¹H NMR, ¹³C NMR和HRMS证实, 与文献所报道相一致.     

Participation in the formation of iodo ureas from 3-buten-1-ol derivatives: A reinvestigation

Treatment of O-substituted derivatives of 3-buten-1-ol with silver cyanate and iodine, followed by ammonia, gave cyclic derivatives 5 and 6. These compounds were previously assigned the linear structures 3 and 4, respectively. Evidence in support of the proposed structural reassignment was obtained from high-field ¹H and ¹³C NMR studies. Both 5 and 6 undergo loss of the ureido group upon treatment with water to give 9 and 10, and 12, respectively. Potential mechanisms for the observed reactions are discussed.     

Stereochemical studies—XVIII : Conformational study of heteroanalogues of bicyclo[3.3.1]nonane

A number of heteroanalogues of bicyclo[3.3.1]nonane containing heteroatoms in 3-, 3,7- and 3,7,9-positions has been synthesized. ¹H NMR measurement has shown that the compounds of the types 4,5 and 6 (Y = oxygen) are double-chairs with the “wings” of the molecule flattened. However, a new conformational effect has been found for the sulfur containing compounds of type 5 and 6 (X,Y = sulfur) which show substantially increased tendency to adopt boat-chair conformations.     

Microwave synthesis,characterization and antimicrobial study of new pyrazolyl-oxopropyl-quinazolin-4(3H)-one derivatives

Heterocyclic compounds containing pyrazolyl-oxopropyl-quinazolin-4(3H)-one are reported to possess significant biological activity. Syntheses of 6-bromo-2-(3-chloro-2-oxopropyl)-3-(4-fluorophenyl)quinazolin-4(3H)-one 2 6-bromo-3-(4-fluorophenyl)-2-(3-hydrazinyl-2-oxopropyl)quinazolin-4(3H)-one 3 and 6-bromo-2-(3-(3-(4-(1-(2-chlorophenyl)-3-methyl-1H-pyrazol-5(4H)-ylideneamino)phenyl)-5-(substituted phenyl)-4,5-dihydro-1H-pyrazol-1-yl)-2-oxopropyl)-3-(4-fluorophenyl)quinazolin-4(3H)-one 5a–j using microwave irradiation have been described. These compounds have been characterized on the basis of the UV, IR, ¹H NMR, ¹³C NMR, Mass and elemental analysis. Compounds have been evaluated for their antimicrobial activity.     

Enantioselective fluorescent sensors for amino acid derivatives based on BINOL bearing benzoyl unit

The derivatives of BINOL, (S)-1 and (R)-1, and their analogues have been prepared and the structures of these compounds have been characterized by IR, MS, ¹H, and ¹³C NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors has been studied by fluorescence titration and ¹H NMR spectroscopy. The receptors exhibited different chiral recognition abilities toward some enantiomers of chiral materials and formed 1:1 complexes between host and guest. Receptor (S)-1 or (R)-1 exhibits excellent enantioselective fluorescent recognition abilities toward amino acid derivatives.