Synthesis and structural revision of naturally occurring ayapin derivatives

The synthesis of three highly oxygenated naturally occurring coumarins, 8-methoxy-6,7-methylenedioxycoumarin, 5-methoxy-6,7-methylenedioxycoumarin and 5,8-dimethoxy-6,7-methylenedioxycoumarin is described for the first time, together with a new method for the preparation of ayapin (6,7-methylenedioxycoumarin). Comparison of the spectroscopic data of the synthetic tetraoxygenated coumarin 5,8-dimethoxy-6,7-methylenedioxycoumarin with literature reports resulted in the structural revision of several natural coumarins. Two coumarins, both identified as 5,8-dimethoxy-6,7-methylenedioxycoumarin must have other structures, while the structure of another coumarin, described as the isomeric 7,8-dimethoxy-5,6-methylenedioxycoumarin has to be revised to 5,8-dimethoxy-6,7-methylenedioxycoumarin.     

Regioselectivity of Diels-Alder reactions between 6,7-dehydrobenzofuran and 2-substituted furans

We describe the first report of the generation of 6,7-dehydrobenzofuran(6,7-benzofuranyne) from 6,7-dihalobenzofurans via metal-halogen exchange and elimination, in a manner similar to our previous work with 6,7-indole arynes. This benzofuranyne undergoes highly regioselective Diels-Alder cycloadditions with 2-substituted furans.     

Seco-Abietanoids from Cryptomeria japonica and Their Inhibitory Activity Toward Xanthine Oxidase

Chemistry of Natural Compounds - A new seco-abietanoid, 12-methoxy-7-oxo-6,7-secoabieta-8,11,13-trien-6-oic acid (1), and a known seco-abietanoid,12-hydroxy-6,7-secoabieta-8,11,13-triene-6,7-dial...     

A Concise Synthesis of 2‐Amino‐1,2,3,4‐tetrahydronaphthalene‐6,7‐diol (‘6,7‐ADTN’) from Naphthalene‐2,3‐diol

2‐Amino‐1,2,3,4‐tetrahydronaphthalene‐6,7‐diol ( 2 ; 6,7‐ADTN) was synthesized starting from naphthalene‐2,3‐diol in seven steps and with an overall yield of 44%. Methylation of naphthalene‐2,3‐diol with dimethyl sulfate, followed by Friedel? Crafts acylation with AcCl, gave 2‐acetyl‐6,7‐dimethoxynaphthalene. 2‐Acetyl‐6,7‐dimethoxynaphthalene was converted to 6,7‐dimethoxynaphthalene‐2‐carboxylic acid by a haloform reaction. Birch reduction of the carboxylic acid with 4 mol‐equiv. of Na in liquid ammonia afforded 1,2,3,4‐tetrahydro‐6,7‐dimethoxynaphthalene‐2‐carboxylic acid, from which 2 was obtained by a Curtius reaction, followed by hydrogenolysis and demethylation.     

Synthesis of 8,9-dialkoxy-substituted tetrahydrobenz[h] isoquinolines

6,7-Dimethoxy-2-naphthylethylamine, prepared by the diborane reduction of 6,7-dimethoxy-2-naphtlialeneacetamide, underwent a Pictet-Spengler cyclization to form 8,9-dimethoxy-1,2,3,4-tetrahydrobenz[h]isoquinoline. This compound is identical with that obtained by reduction of the corresponding dihydrobenzisoquinoline prepared from formamide cyclization. 6,7-Dialkoxy-2-naphthaleneacetic acids, the key intermediates for the preparation of these amides, were obtained from 6,7-dialkoxy-2-acetonaphthones by a modified Willgerodt reaction.     

Polycyclic N-hetero compounds. XXXIII. Syntheses of 4-substituted 6,7-dihydro-5H-benzo[6,7]-cyclohepta[1,2-d]pyrimidines and their inhibitory activities on platelet aggregation and on reserpine-induced hypothermia

Various 4-substituted 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d]pyrimidines were synthesized by the reaction of 4-chloro-6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d]pyrimidine with amines. Their inhibitory activities against collagen-induced platelet aggregation and also against reserpine-induced hypothermia in mice were investigated.     

The structure of covalent hydrates of alloxazines. A reinvestigation

It is shown by ¹³C-NMR. and synthesis of 6,7-dimethyl-3-ethoxycarbonylamino-quinoxaline-2-carboxamide ( 5 ) and methyl 6,7-dimethyl-3-(N′-methylureido)-quinoxaline-2-carboxylate ( 6 ) that hydrolysis of lumichrome ( 1 , R = H) must yield 6,7-dimethyl-3-ureidoquinoxaline-2-carboxylic acid ( 2 , R = H) and not 6,7-dimethyl-2-oxo-1,2,9,9a-tetrahydrooxazolo[4,5-b]quinoxaline-9a-carboxamide ( 2a , R = H), as previously proposed.     

Cinnoline chemistry. XIV. 3-cyclohexylcinnolines

The synthesis of 3-cyclohexyl-6,7-dimethoxy-1H-4-cinnolone ( 4 ), 4-chloro-3-cyclohexyl-6,7-dimethoxycinnoline ( 5 ) and 8-bromo-3-cyclohexyl-6,7-dimethoxy-1H-4-cinnolone ( 6 ) are reported.     

New Aryl Derivatives of Quinolinedione and Related Heterocyclic Compounds

The synthesis of new derivatives of 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione via palladium/Sphos‐mediated Suzuki–Miyaura cross‐coupling reaction is reported. The 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione intermediates were prepared in a three‐step reaction from 8‐hydroxyquinoline. The palladium‐catalyzed reactions of 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione with a variety of aryl boronic acids provide coupled compounds in high yields. The arylation of 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione with 4‐bromophenyl boronic acid supplied 6,6′‐(1,4‐phenylene)bis(7‐bromoquinoline‐5,8‐dione) and (4‐(6‐(4‐(6‐chloro‐5,8‐dihydroquinolin‐7‐yl)phenyl)‐5,8‐dihydroquinolin‐7‐yl)phenyl)boronic acid respectively, in addition to the expected coupled compounds in moderate yields. Also, Pd(0)/PPh₃ allowed the 7‐chloro‐6‐(4‐nitrophenyl)quinoline‐5,8‐dione and 7‐chloro‐6‐phenylquinoline‐5,8‐dione to be synthesized via Heck reaction. The yields of the synthesized target molecules depend largely on the reaction conditions and the type of ligands employed. Structural assignments of the synthesized compounds were established by spectra and analytical data.     

Über Pterinchemie. 62. Mitteilung. Protonenkatalysierte [1,2]-H-Verschiebung bei der Umlagerung von 6,7-Diphenyl-5,6-dihydropterin zu 6,7-Diphenyl-7,8-dihydropterin

Proton catalysed [1,2]-H-shift in the rearrangement of 6,7-diphenyl-5,6-dihydropterine (I) to 6,7-diphenyl-7,8-dihydropterine (III) The arrangement from I to the thermodynamically more stable III undergoes through a acid catalysed [1,2]-H-shift (intramolecular 6,7-hydride rearrangement) (see Scheme 1).     

Polycyclic N-hetero compounds. XXXV. Syntheses and anti-platelet aggregation activity of 5,6-Dihydro-4H-benzo[3,4]cyclohept[1,2-e]imidazo[1,2-c]pyrimidines with an oxygen function at the 1-position

Various 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d][pyrimidines bearing amino acid group at the 4-position of the skeleton were synthesized by the reaction of 4-chloro-6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d]-pyrimidine with some amino acid, which were cyclized to 5,6-dihydro-4H-benzo[3,4]cyclohept[1,2-e]imidazo-[1,2-c]pyrimidines, corresponding to B-homo-11,13,15-triazasteroids. Their inhibitory activities against platelet aggregation induced by collagen were also investigated.     

Über Pterinchemie. 57. Mitteilung. Zur Konfiguration und Konformation von 6,7-Dimethyl-und 5,6,7-Trimethyl-5,6,7,8-tetrahydropterin

Configuration and conformation of 6,7-Dimethyl- and 5,6,7-Trimethyl-5,6,7,8-tetrahydropterines. During the hydrogenation of 6,7-dimethylpterine, cis-6,7-dimethyl-tetrahydropterine is formed. A possible conformation for this substance and for the 5,6,7-trimethyl derivative, which is obtained from it, is discussed, taking the ¹H-NMR. spectra of both tetrahydropterines into consideration.     

Spatial Configuration of Derivatives of 5,5a,6,7-Tetrahydropyrido[1,2-a]benzimidazole and 6,7-Dihydro-5aH-pyrido[1,2-b]benzoxazole

The spatial configurations of 7,9-diphenyl-5a,6-tetramethylene-5,5a,6,7-tetrahydropyrido[1,2-a]benzimidazole and 7,9-diphenyl-5a,6-tetramethylene-2,5a,6,7-tetrahydropyrido[1,2-a]benzimidazol-2-one have been established by X-ray crystallography. Analogous configurations are proposed for a series of other derivatives of 5,5a,6,7-tetrahydropyrido[1,2-a]benzimidazoles and some derivatives of 6,7-dihydro-5aH-pyrido[1,2-b]benzoxazoles on the basis of ¹H NMR spectroscopic data and the results of quantum chemical calculations using the MNDO, AM1, and PM3 methods.     

Synthesis of 2,4-substituted 6,7-phenanthreno-and 6,7-acenaphthenopteridines

A series of 6,7-phenanthreno- and 6,7-acenaphthenopteridines bearing different substituents at positions 2 and 4 are prepared. The structures of the compounds are confirmed by spectroscopic studies and elemental analyses.     

Rapid preparation of isotopolog libraries by in vivo transformation of 1)C-glucose. Studies on 6,7-dimethyl-8-ribityllumazine, a biosynthetic precursor of vitamin B2

An Escherichia coli strain engineered for expression of the ribABGH genes of Bacillus subtilis was shown to produce 100 mg of the riboflavin precursor 6,7-dimethyl-8-ribityllumazine per liter of minimal medium. Growth of the recombinant strain in medium supplemented with [U-13C6]glucose and/or 15NH4Cl as single sources of carbon and/or nitrogen afforded 6,7-dimethyl-8-ribityllumazine universally labeled with 13C and/or 15N. The yield of [U-13C13]-6,7-dimethyl-8-ribityllumazine based on [U-13C6]glucose was 25 mg/g. Fermentation with [1-13C1]-, [2-13C1]-, or [3-13C1]glucose afforded mixtures of 6,7-dimethyl-8-ribityllumazine isotopologs, predominantly with 13C enrichment of single carbon atoms. The isotope-labeled samples enabled a comprehensive NMR analysis of 6,7-dimethyl-8-ribityllumazine. Isotopolog libraries of a wide variety of microbial metabolites can be produced by the same experimental approach.     

Proton magnetic resonance spectra of some 6- and 7-substituted 2-amino-4-hydroxypteridines

The conformations in solution of 6-phenyltetrahydropterin, 6,7-diphenyltetrahydropterin and 6-7, dimethyltetrahydropterin have been determined from their proton magnetic resonance spectra. The 6-phenyltetrahydropterin has the reduced pyrazine ring in a half chair conformation with the phenyl ring in the equatorial position. Both the 6,7-diphenyl- and 6,7-dimethyltetrahydropterins are of the cis configuration and have one substituent in an axial position. The enzymatic activity of these cofactors may be related to these conformations.     

Two new diterpenoids from Isodon serra

From the aerial part of Isodon serra,two new ent-6,7-seco-kaurane-type diterpenoids,15α,20β-dihydroxy-6β-methoxy-6,7- seco-6,20-epoxy-1,7-olide-ent-kaur-16-ene (1) and 6α,15α-dilaydroxy-20-aldehyde-6,7-seco-6,11α-epoxy-1,7-olide-ent-kaur-16- ene (2) were isolated.Their structures were elucidated by spectroscopic means.     

Complete assignments 1H and 13C NMR spectral data of four anabaseine derivatives

The anabaseine derivatives 6-methoxy-7-hydroxy-1-(pyridin-3-yl)-3,4-dihydroisoquinoline, 6,7-dimethoxy-1-(pyridin-3-yl)-1,2,3,4-tetrahydroisoquinoline and 6,7-dimethoxy-1-(piperidin-3-yl)-1,2,3,4-tetrahydroisoquino- line were prepared either by demethylation with HBr or by reduction with different reagents, NaBH4 and H2/PtO2 from 6,7-dimethoxy-1-(pyridin-3-yl)-3,4-dihydroisoquinoline, as starting material. The structures have been fully assigned by the combination of one- and two-dimensional experiments.     

Rovibrational spectra of LiH2+, LiHD+ and LiD2+ determined from FCI property surfaces

Full configuration interaction (FCI) has been used in conjunction with the lithium [6s5p3d1f] (Iron, M. A.; et al. Mol. Phys. 2004, 101, 1345) and hydrogen aug-cc-pVTZ basis sets to construct an 83-point potential energy surface of the 1A1 ground state of 7LiH2+. Vibrational and rovibrational wave functions of the (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+ ground states were calculated variationally using an Eckart-Watson Hamiltonian. For (7)LiD2+, rovibrational transition frequencies for K = 0, 1, 2 and J < or = 10 are within ca. 0.1% of recent experimental values (Thompson, C. D.; et al. J. Chem. Phys. 2006, 125, 044310). A 47-point FCI dipole moment surface was embedded in the rovibrational Hamiltonian to calculate vibrational and rovibrational radiative properties. At 296 K, with v < or = 4 and J < or = 4, the 2(02) <-- 3(03) rotational transition in the |001> band was found to have the greatest spectral intensity with respect to the ground electronic states of (6,7)LiH2+, (6,7)LiHD+, and (6,7)LiD2+. In each case, the most intense rovibrational transitions have been assigned unequivocally using the J, Ka, Kc assignment scheme.     

Reaction of lumichrome or 2-thiolumichrome with alkylamines

The reaction of lumichrome ( 2 ) with alkyl (or allyl)amines such as n-butylamine, n-hexylamine and allylamine gave 2,3-disubstituted 6,7-dimethylquinoxalines 4a-d, 5a-d, 6a-d, 7a-d and 8a-d . Similar reaction of 2-thiolumichrome ( 3 ) with alkyl (or allyl)amines gave 2,3-disubstituted 6,7-dimethylquinoxalines 6a-c, 9a-c and 10a-c , 2-alkyl (or allyl)amino-6,7-dimethyl-3,4-dihydrobenzo[g]pteridine-4-ones 11a-c and 2,4-dialkyl (or allyl)amino-6,7-dimethylbenzo[g]pteridines 12a-c .