Efficient and highly diastereoselective preparation of a myrtenal derived bis-sulfoxide and its preliminary evaluation as chiral acyl donor

Treatment of disulfide 7 with NaIO₄ in EtOH at rt gave monosulfoxide 8 (95%), while at 50 °C it gave trans-bis-sulfoxide 6a (84%, >99% de). In contrast, treatment of 7 with MCPBA gave bis-sulfone 9 (95%). The anion of 6a reacted with benzaldehyde affording carbinol 10 (76%, >99% de). The absolute configuration of 8, 6a, and 10 was established by single crystal X-ray diffraction analyses.     

Novel photo-induced oxidative cyclization of 1,3-dimethyl-5-(1-arylmethylidene)pyrimidine-2,4,6(1,3,5H)-triones: synthesis and properties of areno[5,6]pyrano[2,3-d]pyrimidine-2,4(1,3H)-dionylium ions and their photo-induced autorecycling oxidizing reaction toward some amines

Novel photo-induced oxidative cyclization was accomplished to synthesize areno[b]pyrimido[5,4-e]pyran-2,4(1,3H)-dionylium ions 13a-c⁺·ClO₄⁻. Furthermore, 13a-c⁺·BF₄⁻ and their phenyl-substituted derivatives 19a,b⁺·BF₄⁻ were alternatively synthesized by the reaction of salicylaldehyde and its naphthyl derivatives with barbituric acids and subsequent treatment with aq. HBF₄. Structural characteristics of 13a-c⁺ and 19a,b⁺ were clarified on inspection of the UV-vis and NMR spectral data as well as X-ray crystal analyses. The electrochemical properties were studied by the CV measurement. In a search for reactivity, reactions of 13a-c⁺·BF₄⁻ with some nucleophiles, hydride, benzylamine, and H₂O, were also carried out. The photo-induced autorecycling oxidation reactions of 13a-c⁺·BF₄⁻ toward some amines under aerobic conditions were carried out to give the corresponding imines (isolated by converting to the corresponding 2,4-dinitrophenylhydrazones) in 643-3600% yield (recycling number of 13a-c⁺·BF₄⁻: 6.4-36.0).     

Total synthesis of (−)-2-epi-lentiginosine by use of chiral 5-hydroxy-1,5-dihydropyrrol-2-one as a building block

We have developed a practical synthesis of the chiral lactam as a new chiral building block for alkaloid synthesis. Lipase-catalyzed kinetic resolution of hydroxylactam 8, followed by isolation-racemization of the chiral acetoxylactam 9 provided the optically pure hydroxylactam 8 in 96.0% yield with >99% ee after five cycles of kinetic resolution-racemization process. Chemical transformation of (S)-hydroxylactam 8 furnished chiral (−)-2-epi-lentiginosine (1) in 20% yield in 10 steps with no loss of enantiomeric excess.     

Preparation, crystal structure, and spectroscopic, chemical, and electrochemical properties of (2E,4E)-4-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1,3-butadiene compared with those of (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene

Wittig reaction of 3-[4-(dimethylamino)phenyl]propanal (5) with (3-guaiazulenylmethyl)triphenylphosphonium bromide (4) in ethanol containing NaOEt at 25 °C for 24 h under argon gives the title (2E,4E)-1,3-butadiene derivative 6E in 19% isolated yield. Spectroscopic properties, crystal structure, and electrochemical behavior of the obtained new extended π-electron system 6E, compared with those of the previously reported (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene (12), are documented. Furthermore, reaction of 6E with 1,1,2,2-tetracyanoethylene (TCNE) in benzene at 25 °C for 24 h under argon affords a new Diels-Alder adduct 8 in 59% isolated yield. Along with spectroscopic properties of the [π4+π2] cycloaddition product 8, the crystal structure, possessing a cis-3,6-substituted 1,1,2,2-tetracyano-4-cyclohexene unit, is shown. Moreover, reaction of 6E with (E)-1,2-dicyanoethylene (DCNE) under the same reaction conditions as the above gives no product; however, this reaction in p-xylene at reflux temperature (138 °C) for four days under argon affords a new Diels-Alder adduct 9 in 54% isolated yield. Although reaction of 6E with DCNE in toluene at reflux temperature (110 °C) for four days under argon provides 9 very slightly, reaction of 6E with dimethyl acetylenedicarboxylate (DMAD) in toluene at reflux temperature for two days under argon yields a new Diels-Alder adduct 10, in 58% isolated yield, which upon oxidation with MnO₂ in CH₂Cl₂ at 25 °C for 1 h gives 11, converting a (CH₃)₂N-4″ into CH₃NH-4″ group, in 37% isolated yield. The crystal structure of 11 supports the molecular structure 10 possessing a partial structure cis-3,6-substituted 1,2-dimethoxycarbonyl-1,4-cyclohexadiene. The title basic studies on the above are reported in detail.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Reaction of guaiazulene with o-formylbenzoic acid in diethyl ether (or methanol) in the presence of hexafluorophosphoric acid: comparative studies on H and C NMR spectral properties of 3-guaiazulenylmethylium- and 3-guaiazulenium-ion structures

Reaction of guaiazulene (1) with o-formylbenzoic acid (2) in diethyl ether in the presence of hexafluorophosphoric acid at 25 °C for 90 min gives the corresponding monocarbenium-ion compound, [2-(carboxy)phenyl](3-guaiazulenyl)methylium hexafluorophosphate (3), quantitatively, which upon treatment with aq NaHCO₃ leads to 3-(3-guaiazulenyl)-2-benzofuran-1(3H)-one (5) in 96% isolated yield. Similarly, reaction of 1 with 2 in methanol under the same conditions as the above reaction affords two kinds of inseparable monocarbenium-ion compounds, 3 and (3-guaiazulenyl)[2-(methoxycarbonyl)phenyl]methylium hexafluorophosphate (4) with an equilibrium between them, which upon reaction with a solution of NaBH₄ in ethanol at 25 °C for 30 min leads to 5 in 46% isolated yield and (3-guaiazulenyl)[2-(methoxycarbonyl)phenyl]methane (6) in 37% isolated yield. Along with the ¹H and ¹³C NMR spectral properties of a solution of 5 in trifluoroacetic acid-d₁ at 25 °C, whose molecular structure is converted to a ca. 1:1 equilibrium mixture of 7 possessing a partial structure of the 3-guaiazulenylmethylium-ion and 8 possessing a partial structure of the 3-guaiazulenium-ion, comparative studies on the ¹H and ¹³C NMR spectral properties of 7 and 8 with those of the monocarbenium-ion compound, (3-guaiazulenyl)[4-(methoxycarbonyl)phenyl]methylium hexafluorophosphate (A), 5, and 6 are reported. From these NMR studies, it can be inferred that the positive charge of the 3-guaiazulenylmethylium-ion part of 7 apparently is transferred to the seven-membered ring, generating a resonance form of the 3-guaiazulenylium-ion structure η′, and the same result can be inferred for the previously documented monocarbenium-ion compounds A-I. Moreover, referring to a comparative study on the C-C bond lengths of A observed by the X-ray crystallographic analysis with those of the optimized (3-guaiazulenyl)[4-(methoxycarbonyl)phenyl]methylium-ion structure for A calculated by a WinMOPAC (Ver. 3.0) program using PM3, AM1, or MNDOD as a semiempirical Hamiltonian, the optimized [2-(carboxy)phenyl](3-guaiazulenyl)methylium-ion structure for 3 calculated using PM3 is described.     

A short-cut from 1-acetyl adamantane to 2-(1-adamantyl)pyrroles

The oxime of 1-acetyl adamantane 2 is added to acetylene (KOH/DMSO, 70 °C, initial acetylene pressure 13 atm, 30 min) to afford the corresponding O-vinyl oxime 5 in 80% yield. The latter upon heating (DMSO, 120 °C, 1 h) gives 2-(1-adamantyl)pyrrole 3, 1-acetyl adamantane 1, and adamantane (6:3:1 mass ratio), the yield of the pyrrole 3 being 83% (based on 1-acetyl adamantane 1 consumed). Under harsher conditions (NaOH/DMSO, 130 °C, atmospheric pressure of acetylene, 4 h) oxime 2 reacts with acetylene to furnish pyrrole 3, 1-acetyl adamantane 1, 1-vinyl adamantane 9, and adamantane (6:7:3:1 mass ratio), with the isolated yield of pyrrole 3 reaching 34%. Under pressure (NaOH/DMSO, 120 °C, initial acetylene pressure 14 atm, 1 h) the same reaction leads to 2-(1-adamantyl)-1-vinylpyrrole 4 and ketone 1 in 48% (based on consumed ketone 1) and 24% yields, respectively. The pyrrole 4 is easily deprotected to the corresponding 1H-pyrrole 3 in 77% yield by treatment (aqueous MeCN) with Hg(OAc)₂ and NaBH₄.     

Ultrasound-assisted convenient synthesis of hypolipidemic active natural methoxylated (E)-arylalkenes and arylalkanones

An ultrasound-assisted convenient method was developed for the conversion of toxic methoxylated cis-isomer of arylalkenes into its hypolipidemic active trans-isomer. Treatment of cis-isomer or mixture of all three isomers (1a-1j) with ammonium formate and 10% Pd/C gave arylalkanes (2a-2j), which upon oxidation with DDQ in anhydrous dioxane containing a little amount of silica gel, provided (E)-arylalkenes (3a-3g) in 42-72% yield depending upon the substituents attached at the aryl ring. The same method, upon addition of a few drops of water, provided hypolipidemic active arylalkanones (3h-3j) in 59-65% yield.     

Enantioselective construction of nitrogen-substituted quaternary carbon centers adjacent to the carbonyl group in the cyclohexane ring: first asymmetric synthesis of anesthetic (S)-ketamine with high selectivity

Enantioselective construction of nitrogen-substituted quaternary carbon centers adjacent to the carbonyl group in the cyclohexane ring was performed with respect to the asymmetric synthesis of anesthetic (S)-ketamine 1. Diastereoselective nucleophilic 1,2-addition reaction of phenyllithium to α-ketoxime-ether acetal 9 bearing chiral auxiliary on the α-carbonyl function gave benzyloxyamine 11 major in 83% yield with 82% de, which was converted to the corresponding amino ketone 12. However, the reaction of 2-chlorophenyllithium did not work in which this route was unavailable for the synthesis of 1. Then, an alternative strategy directed toward 1, starting with a compound having 2-chlorophenyl groups in advance, was designed in which the chiral quaternary carbon center bearing a nitrogen atom in the ring is created by the enantioselective reduction of the atropisomeric intermediate ketone 18, and the sequential allyl cyanate-to-isocyanate rearrangement with complete 1,3-chirality transfer. The first asymmetric synthesis of 1 with excellent selectivity (>99% ee) was accomplished by a short path according to the strategy.     

Lipase-catalyzed kinetic resolution of thiotetronic acid derivatives bearing a chiral quaternary carbon: total synthesis of (R)-thiolactomycin and its O-analogue

We have developed a chemoenzymatic synthesis of (R)-thiolactomycin (1) having a chiral quaternary carbon atom at C5. In the kinetic resolution of the thiotetronic acid precursor 4, both enantiomers were obtained with high enantiomeric excess by use of Chirazyme^® L-2. Chemical transformations of the (R)-alcohol 4 provided the chiral (R)-thiolactomycin (1) in 36% yield in five steps.     

Development of a Double Allylboration Reagent Targeting 1,5-syn-(E)-Diols: Application to the Synthesis of the C(23)-C(40) Fragment of Tetrafibricin

Interest in the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin prompted us to develop a new method for the synthesis of 1,5-syn-(E)-diols. Toward this end, the kinetically controlled hydroboration of allenes 6, 33, ent-39, 42, and 45 with the Soderquist borane 25R were studied. Tetrabutylammonium allenyltrifluoroborate 45 gave superior results and was utilized in a double allylboration sequence with two different aldehydes to provide the targeted 1,5-syn-(E)-diols in generally high yields (72-98%), and with high enantioselectivity (>95% ee), diastereoselectivity (dr >20:1), and (E)/(Z) selectivity (>20:1). This new method was applied to the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin.     

Synthesis of (S)-2-amino-7-methoxytetralin and isoindolo[1,2-a]isoquinolinone derivatives from l-aspartic acid

This paper describes a new total synthesis for (S)-2-amino-7-methoxytetralin, (S)-7-MeO-AT, from l-aspartic acid in an overall yield of 10% over nine steps. The major loss was ascribed to a key intramolecular Friedel–Crafts cyclization step, which afforded up to 36% yield. Attempts to perform a Friedel–Crafts cyclization of an intermediate phthalimide protected amino alcohol 13 did not give the desired protected (S)-7-MeO-AT. On the other hand, two new isoindolo[1,2-a]isoquinolinone derivatives 14 and 15, were isolated in 21 and 11% yield, respectively. The yield of 15 was improved to 70%.     

Synthesis of the fungal natural product (−)-xylariamide A

The first synthesis of the fungal natural product (−)-xylariamide A 1 is reported. N,O-Bis(trimethylsilyl)acetamide induced coupling of d-tyrosine with (E)-but-2-enedioic acid 2,5-dioxo-pyrrolidin-1-yl ester methyl ester 5 produced the dechloro natural product 6, which was subsequently monochlorinated using oxone and KCl to yield synthetic 1. (−)-Xylariamide A 1, (+)-xylariamide A 2 and (−)-dechloroxylariamide A 6 displayed no cytotoxic or antimicrobial activity.     

Biomimetically inspired total synthesis of (12S)-12-hydroxymonocerin and (12R)-12-hydroxymonocerin

A concise asymmetric total synthesis of (12S)-12-hydroxymonocerin (1) and (12R)-12-hydroxymonocerin (2) were efficiently achieved from the known 4-bromo-2,6-dimethoxyphenol. The synthetic approach was inspired by our biomimetic synthesis of (+)-monocerin (3) and 7-O-demethylmonocerin (4). The cis-fused furobenzopyranones of 1 and 2 was efficiently constructed via an intramolecular nucleophilic trapping of a quinonemethide intermediate, which was obtained by benzylic oxidation of compound 10 using 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).     

Synthetic studies of erythromycin derivatives: 6-O-methylation of (9S)-12,21-anhydro-9-dihydroerythromycin A derivatives

Synthetic studies on methylation of erythromycin derivatives were conducted. Methylation of 6 resulted in the formation of the C-3′ quaternary ammonium salts with a rate faster than 6-O-methylation. In dipolar aprotic solvent and under strong base conditions, 6-O-methylation, C-3′ quaternary ammonium salts formation and 2-C-methylation proceeded simultaneously to yield a mixture of three different products 7, 8 and 9. The quaternary ammonium salts were converted back to the corresponding tertiary amines 2, 10 and starting material 6 by employing sodium 4-pyridinethiolate as a N-demethylation reagent. The 6-O-methylation was eventually achieved in a good yield when a carbobenzyloxy (Cbz) group was utilized to protect the C-3′-dimethylamino group of 4. In this report, we will discuss the details of different reaction courses in the methylation of (9S)-12, 21-anhydro-9-dihydroerythromycin A derivatives.     

Facile synthesis of 4-phenylquinolin-2(1H)-one derivatives from N-acyl-o-aminobenzophenones

An efficient synthesis of 4-phenylquinolin-2(1H)-one derivatives has been achieved in a one-pot reaction from N-acyl-o-aminobenzophenones 1a-c (a: acyl=acetyl; b: acyl=propanoyl; c: acyl=heptanoyl) using NaH as a base. Treatment of 1 with NaH provided the quinolones 2a-c with 62-83% yields, whereas the reaction in the presence of alkyl iodide (alkyl=methyl, ethyl, n-octyl) gave the corresponding N-alkylated quinolones 3a-g in 75-95% yields. The alkylation reaction of 4-phenylquinolin-2(1H)-one 2a with alkyl halide gave a mixture of N-alkylated and O-alkylated products. Comparison of IR and NMR data of the N-alkylated and O-alkylated compounds with those of 2a-c indicated that 2a-c exist as the lactam form.     

Microbial transformation of (−)-Huperzine A

Five products were yielded from the transformation of (−)-Huperzine A (1) by Streptomyces griseus CACC 200300. Their structures were determined as 16-hydroxyl huperzine A (2), 14α-hydroxyl huperzine A (3), huperzine A 8α,15α-epoxide (4), 13N-formyl huperzine A (5), and 13N-acetyl huperzine A (6) on the basis of their chemical and physical data. It is the first report on the microbial transformation of (−)-Huperzine A and would facilitate further structural modification by chemo-enzymatic method.     

Bioactive meroditerpenes and indole alkaloids from the soil fungus Neosartorya fischeri (KUFC 6344), and the marine-derived fungi Neosartorya laciniosa (KUFC 7896) and Neosartorya tsunodae (KUFC 9213)

Two new metabolites including a new aszonalenin analogue (1c) and a new meroditerpene (3) were isolated, together with aszonalenin (1a), acetylaszonalenin (1b), 13-oxofumitremorgin B (2), aszonapyrone A (4b) and helvolic acid, from the culture of the soil fungus Neosartorya fischeri (KUFC 6344). While the ethyl acetate extract of the culture of the diseased coral-derived fungus Neosartorya laciniosa (KUFC 7896) furnished aszonapyrone B (4a), aszonapyrone A (4b), tryptoquivaline L and 3′-(4-oxoquinazolin-3-yl) spiro[1H-indole-3,5′-oxolane]-2,2′-dione, the ethyl acetate extract of the culture of the marine sponge-associated fungus Neosartorya tsunodae (KUFC 9213) yielded a new analogue of chevalone C (5) and helvolic acid. The structures of the new compounds were established based on 1D and 2D NMR spectral analysis as well as HR-ESIMS. Compounds 1a–c, 2, 3, 4a, 4b and 5 were evaluated for their in vitro growth inhibitory activity on the MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer) and A375-C5 (melanoma) cell lines by the protein binding dye SRB method.     

Ring transformation of cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium ion to the corresponding pyrrole derivatives via troponeimine intermediates: photo-induced autorecycling oxidizing reactions of some amines

Ring transformation of 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]furan- 8(7H),10(9H)-dionylium tetrafluoroborate 4⁺·BF₄⁻ to 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrrole-8(7H),10(9H)-dionylium tetrafluoroborate 6a-d⁺·BF₄⁻ consists of the reaction of 4⁺·BF₄⁻ with amines and subsequent exchange of the counter-ion using aq. HBF₄. Reactions of 4⁺·BF₄⁻ with aniline and 4-substituted anilines afforded the corresponding pyrrole derivatives 6a-c⁺·BF₄⁻ directly in good yields. On the other hand, reaction of 4⁺·BF₄⁻ with benzylamine gave the troponeimine intermediate 9, which was not converted to 6d⁺·BF₄⁻ and reverted to 4⁺·BF₄⁻ by adding HBF₄; however, it was converted to 6d⁺·BF₄⁻ upon treatment with (COCl)₂ or SOCl₂, followed by exchange of the counter-ion. In a search for the characteristics of 9, inspection and comparison of the X-ray crystal analyses, NMR and UV-vis spectra, and CV measurement of 9 and N,N-disubstituted troponeimine derivatives 12 were carried out to suggest the remarkable structure of 12 having ionic C-O bonding between the imine-carbon atom and the oxygen atom of the barbituric acid moiety in the solid state. Thus, characteristics of 9 were ascribed to the sterically hindered and favorable conformation of N-protonated troponeimine intermediates. Furthermore, novel photo-induced oxidation reactions of a series of 4⁺·BF₄⁻, 5⁺·BF₄⁻, and 6a,e⁺·BF₄⁻ towards some amines under aerobic conditions were carried out to give the corresponding imines in 455-8362% yields [based on compounds 4⁺, 5⁺, and 6a,e⁺], suggesting the oxidation reaction occurs in an autorecycling process. Mechanistic aspects of the amine-oxidation reaction are also postulated.     

Synthesis, properties, and oxidizing function of 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates

Uracil-annulated heteroazulenes, 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates 7a,b·BF₄⁻, which are the isoelectronic compounds of 5-dezazaflavin, were synthesized. X-Ray crystal analysis and MO calculations were carried out to clarify the structural characteristics of 7a,b·BF₄⁻. The stability of cations 7a,b is expressed by the pK_R+ values which were determined spectrophotometrically to be 10.9 and 11.2, respectively. The electrochemical reduction of 7a,b exhibited high reduction potentials at −0.84 and −0.87 (V vs Ag/AgNO₃) upon cyclic voltammetry (CV). A good linear correlation between the pK_R+ values and reduction potentials (E1_red) of 7a,b·BF₄⁻ and reference compounds 4·BF₄⁻ and 5·BF₄⁻ was obtained. In a search of the reactivity, reactions of 7a,b·BF₄⁻ with some nucleophiles, hydride and diethylamine, were carried out to clarify that the introduction of nucleophiles to give regio-isomers is dependent on the nucleophile. The photo-induced oxidation reactions of 7a,b·BF₄⁻ toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compounds 7a,b·BF₄⁻], suggesting the oxidizing function of 7a,b·BF₄⁻ toward alcohols in the autorecycling process.