Synthesis of [Gly-1]RA-VII, [Gly-2]RA-VII, and [Gly-4]RA-VII. Glycine-containing analogues of RA-VII, an antitumor bicyclic hexapeptide from Rubia plants

Three analogues of RA-VII (1), an antitumor bicyclic hexapeptide from Rubia plants, were synthesized. Three analogues, [Gly-1]RA-VII (4), [Gly-2]RA-VII (5), and [Gly-4]RA-VII (6), in which one of the three alanine residues in 1 was replaced by a glycine residue, were prepared by linking of the cycloisodityrosine unit, obtained by degradation of 1, to three different glycine-containing tetrapeptides followed by macrocyclization. Of these three analogues, analogue 4 showed the highest cytotoxic activity. The NMR study revealed that in solution the conformer structures and their ratios of analogue 4 were very similar to those of natural peptide 1, suggesting that the methyl groups at Ala-2 and Ala-4 should be essential for producing the bioactive conformation, whereas that at D-Ala-1 is not essential.     

Semisynthesis of an analogue of antitumor bicyclic hexapeptide RA-VII by fixing the Ala-2/Tyr-3 bond to Cis by incorporating a triazole cis-amide bond surrogate

We prepared an analogue of an antitumor bicyclic hexapeptide RA-VII whose amide configuration between residues 2 and 3 was fixed to cis by incorporating a triazole cis-amide bond surrogate. This analogue was shown, by NMR studies, to take almost the same conformation as that of the minor conformer of RA-VII. It showed no cytotoxic activity.     

Solution forms of an antitumor cyclic hexapeptide, RA-VII in dimethyl sulfoxide-d6 from nuclear magnetic resonance studies.

Using high-resolution proton nuclear magnetic resonance (1H-NMR) and carbon-13 nuclear magnetic resonance (13C-NMR) experiments, we have assigned three discernible configurational isomers observed in dimethyl sulfoxide-d6 (DMSO-d6) for an antitumor cyclic hexapeptide, RA-VII isolated from Rubia cordifolia. The largest isomer, amounting to 64%, has been assigned as conformer A with only a cis configuration between Tyr-5 and Tyr-6. The second configurational isomer, accounting for 32%, has adopted cis configurations between both Tyr-5 and Tyr-6 and between Ala-2 and Tyr-3. The third isomer, amounting to 4%, was determined to have cis configurations for all of the three N-methyl amide bonds.     

New antitumor bicyclic hexapeptides, RA-XI, -XII, -XIII and -XIV from Rubia cordifolia.

Four new bicyclic hexapeptides, named as RA-XI, -XII, XIII and -XIV were isolated from Rubia cordifolia and showed potent antitumor activities against P-388. The structures were elucidated from spectroscopic and chemical evidences. RA-XII, XIII and -XIV were proved to be unique bicyclic hexapeptidic glucosides.     

Synthesis of 2-R-fluorantheno[2,3-d]- and 2-R-fluorantheno[3,2-d]oxazoles

2-R-Fluorantheno[2,3-d]- and 2-R-fluorantheno[3,2-d]oxazoles were synthesized, and their UV and IR spectra were studied. Ten new compounds are described.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 905–907, July, 1974.     

Synthesis of oxazoles from α,β-unsaturated carbonyl compounds through 2-acylaziridines

Oxidative addition of N-aminophthalimide to benzylideneacetone and chalcones followed by thermolysis of the arising 2-aryl-3-acyl-1-phthalimidoaziridines led to the formation of 2,5-disubstituted oxazoles in an overall yield 30–55%. Electron-donor substituents in the aryl fragment of 2-aryl-3-aroyl-1-phthalimidoaziridines accelerate their conversion into oxazoles, and similar substituents in the aroyl fragment retard this process. The possibility was demonstrated of going over to oxazoles from α,β-unsaturated carbonyl compounds via 2-acyl-1-sulfonylaziridines employing chloramine-B. However ethyl 2 cyanocinnamate reacted with chloramine-B with the rupture of the C=C bond and the formation of N-benzylidene-benzenesulfamide.     

Synthesis of 5,6-dihydro-4H-pyrrolo[1, 2-a] [1,4]benzodiazepines

The title compounds are. Prepared by the reaction of carbonyl compounds with 1-(2′-amino-methylphenyl)pyrrole hydrochloride.     

Synthesis of substituted tetrahydropyrimido-[4, 5-b][1, 7]naphthyridines as potential antitumor agents

The synthesis of two linear trisubstituted 6, 7, 8, 9-tetrahydropyrimido[4, 5-b][1, 7]naphthyridines 1 and 3 were accomplished by the regiospecific cyclocondensation of two disubstituted 6-aminopyrimidines 10 and 11 with the ketoaldehyde 1-benzyl-4-hydroxymethylene-3-piperidone. Catalytic debenzylation of 1 afforded the disubstituted compound 2 . The linear structures of 1–3 were established by ¹H nmr and 13C nmr.     

Isomerization of 5-(2H-Azirin-2-yl)oxazoles: An Atom-Economic Approach to 4H-Pyrrolo[2,3-d]oxazoles

An atom economical method for the preparation of variously substituted 4H-pyrrolo[2,3-d]oxazoles was developed on the basis of thermal isomerization of 5-(2H-azirin-2-yl)oxazoles. The latter were prepared by Rh₂(oct)₄ catalyzed reaction of 2-(3-aryl/heteroaryl)-2-diazoacetyl-2H-azirines with a set of substituted acetonitriles, benzonitriles, acrylonitrile and fumaronitrile. According to DFT calculations the transformation of 5-(2H-azirin-2-yl)oxazole to 4H-pyrrolo[2,3-d]oxazole occurs through the nitrenoid-like transition state to give a 3aH-pyrrolo[2,3-d]oxazole intermediate, followed by 1,5-H-shift.     

Synthesis of fused dihydropyrano(furano)pyridines via [4 + 2]-cycloaddition of 5-alkenoxy substituted oxazoles

A three-step procedure to access fused pyridines has been developed utilizing inexpensive amino acids and alkenols to form the key oxazole precursors. Yields are good to excellent and provide a rapid and inexpensive route to a range of pharmacologically and biologically valuable fused pyridines with difficult to access substitution patterns.     

Synthesis of [2]- and [3]rotaxanes through Sonogashira coupling

The synthesis of new [2]- and [3]rotaxanes through Sonogashira coupling has been accomplished in the aim to built oligo(phenyleneethynylene) (OPE) encircled by crown ethers. Optimization of the Sonogashira coupling for the formation of the [2]rotaxane (capping reaction) is presented and the best method has been applied for the synthesis of the longer [3]rotaxane.     

Synthesis and crystal structures of Cd[AlCl4]2 and Cd2[AlCl4]2

Colorless single crystals of Cd[AlCl₄]₂ grow from the melt of CdCl₂ and AlCl₃ upon slow cooling from 250°C. The crystal structure [monoclinic, P1a1, Z = 2, a = 1288.7(2), b = 660.2(1), c = 705.1(1) pm, β = 92.89(1)º] may be derived from hexagonally closest packed layers of Cl^?. Octahedral and tetrahedral holes are filled with Cd²⁺ and Al³⁺ in a 1:2 ratio between all layers stacked in the [104] direction. Cd[GaCl₄]₂ and Cd[AlBr₄]₂ are isotypic. Reduction of Cd[AlCl₄]₂ with excess cadmium shot and slow cooling from 350°C yields plate-like very moisture-sensitive, colorless single crystals of Cd₂[AlCl₄]₂. The crystal structure [triclinic, C1 , Z = 2, a = 655.47(3), b = 1135.26(1), c = 935.23(6) pm, α = 89.70(2)º, β = 103.61(1)º, γ = 90.455(1)º] is built from slabs stacked in the [100] direction consisting of ethane-like [Cd₂Cl₆] units with a Cd? Cd distance of 256.1 pm sharing common vertices with [AlCl₄] tetrahedra.     

Synthesis of 2-methylphenanthro[2, 1-d]thiazole

2-Methylphenanthro[2, 1-d]thiazole has been synthesized by the oxidative cyclization of 2-thioacetylaminophenanthrene.     

Diastereoselective and Enantioselective Synthesis of Multi-Functionalized Isoxazoline-N-Oxides through Asymmetric [4+1] Annulations

A diastereoselective and enantioselective formal [4+1] ylide annulation of chiral sulfonium salts with various substituted Morita-Baylis-Hillman (MBH) adducts leading to optically active isoxazoline N-oxides with three chiral carbon centers has been explored. The salient features of this methodology include a high diastereo- and enantioselective transformation, easily accessible starting materials, and mild reaction conditions. In addition, the isoxazoline N-oxides products can be conveniently transformed into functionalized compounds.     

Synthesis of 1, 2-diazabicyclo [2.2.2] octane, 1, 2-diazabicyclo [3.2.1]-octane,and their derivatives

1, 2-Diazabicyclo [2.2.2] octane, its 6-methyl homolog, and 1, 2-diazabicyclo [3.2.1] octane are synthesized by a general method involving nitrosation of piperidine carboxylic acids, subsequent reduction to 1-aminopiperidine carboxylic acids, cyclization to 3-keto-1, 2-diazabicycloalkanes, reduction of the latter to 1, 2-diazabicycloalkanes. A number of 2-substituted 1, 2-diazabicyclo [2.2.2] octanes are synthesized.     

Facile Regioselective Synthesis of 2-Methyl Furo [3,2-c][1] benzopyran-4-one 2-Methyl Furo[2,3-c] [1]benzopyran-4-one

The title compounds (7 &8) were obtained in excellent yields from 4-[2′-chloroprop-2′-enyloxy] [1] benzopyran-2-one (5) and 3-[2′-chloroprop-2-enyloxy][1]benzopyran-2-one (6) via [3,3] sigmatropic rearrangement and cyclisation of the intermediate chloroallylic enols with conc. H₂SO₄. The reaction was also studied in N,N-dimethyl aniline.     

Synthesis of 1, 4-Bis[3-N-propionyl-2-aryl-1, 3, 4- oxadiazoline-5-yl]phenylenes

1, 3, 4-Oxadiazoline derivatives are found to possess significant biological activities such as antifungal1, insecticidal2, CNS depressant3-5, anticonvulsant effects and plant growth accelerator. They are highly important heterocycles, and have been used …     

Synthesis of 2-mercaptothieno[3,2-d]- and 2-mercaptobenzo[4, 5]thieno[2,3-d]thiazoles

2-Mercaptothieno[3,2-d]- and 2-mercaptobenzo[4, 5]thieno[2,3-d]thiazoles were synthesized by reduction of bis(3,3′-nitro-2,2′-thienyl) and bis(2,2′-nitrobenzo[b]thien-3,3′-yl) disulfides, respectively, with sodium hydrosulfite or sodium sulfide in the presence of carbon disulfide.