Organic syntheses based on 2-oxoglutaric acid. V. Syntheses of novel 2H-1,4-benzothiazines and a 2,5-dihydro-1,5-benzothiazepine

Syntheses aimed on the incorporation in heterocycles of segments originating in the precursor 2-oxoglutaric acid are described. Cylocondensation of dimethyl 2-oxoglutarate 1 , dimethyl 3-bromo-2-oxoglutarate 2 , and dimethyl (E)-2-oxoglutaconate 3 with 2-aminobenzenethiol gave rise to the novel 2H-1,4-benzothiazines 4 and 5 , and the 2,5-dihydro-1,5-benzothiazepine 6 , respectively, by incorporation of either the segments C-1/C-2 or C-2/C-3 or C-3/C-4/C-5 of the precursor.     

C-2/c-3 annulation and C-2 alkylation of indoles with 2-alkoxycyclopropanoate esters

The annulation reaction between various indoles and 2-alkoxycyclopropanoate esters is reported. Both high efficiency and complete stereochemical control were observed in some cases with this annulation process. A single stereocenter on the cyclopropane controls the diastereoselective formation of up to four new stereocenters. A different reaction course was observed with 3-substituted indole substrates, and an intervening C-3 to C-2-migration process arose that gives synthetically useful C-2 alkylation indole products.     

Synthesis of azacyclic 2-deoxy-KDO

Azacyclic analogues of 2-deoxy-KDO have been synthesized from KDO via reductive amination at C-2 and ring closure on C-6 with double inversion.     

Palladium catalysis for the synthesis of hydrophobic C-6 and C-2 aryl 2'-deoxynucleosides. Comparison of C-C versus C-N bond formation as well as C-6 versus C-2 reactivity

Suzuki-Miyaura cross-coupling of haloaromatic compounds with arylboronic acids provides a simple entry to biaryl systems. Despite its ease, to date, there are no detailed investigations of this procedure for deoxynucleoside modification. As shown in this study, a wide variety of C-6 arylpurine 2'-deoxyriboside (C-6 aryl 2'-deoxynebularine analogues) and C-2 aryl 2'-deoxyinosine analogues can be conveniently prepared via the Pd-mediated cross-coupling of arylboronic acids with the C-6 halonucleosides, 6-bromo- or 6-chloro-9[2-deoxy-3,5-bis-O-(tert-butyldimethylsilyl)-beta-D-erythro-pentofuranosyl]purine (1 and 2), and the C-2 halonucleoside, 2-bromo-O(6)-benzyl-3',5'-bis-O-(tert-butyldimethylsilyl)-2'-deoxyinosine (3). Although bromonucleoside 1 proved to be a good substrate for the Pd-catalyzed Suzuki-Miyaura cross-couplings, we have noted that for several C-6 arylations, the chloronucleoside 2 provides superior coupling yields. Also described in this study is a detailed evaluation of catalytic systems that led to optimal product recoveries. Finally, a comparison of the C-C and C-N bond-forming reactions of deoxynucleosides is also reported. On the basis of this comparison, we provide evidence that C-N bond formation at the C-6 position, leading to N-aryl 2'-deoxyadenosine analogues, is more sensitive to the ligand used, whereas C-C bond-forming reactions at the same position are not. In contrast to the ligand dependency exhibited in C-N bond formation at the C-6 position, comparable reactions at the C-2 position of purine deoxynucleosides proceed with less sensitivity to the ligand used.     

Brominated derivatives of 4-hydroxy- and 4-methoxy-6-methyl-2H-pyran-2-ones

Twenty-five different brominated derivatives of 4-hydroxy-6-methyl-2-pyrone (triacetic acid lactone) and 3-acetyl-4-hydroxy-6-methyl-2-pyrone (dehydroacetic acid) have been prepared. Fifteen derivatives have not been previously described and the preparations of a few known products have been improved. Bromination at C-3, C-5, methyl group at C-6 and deacetylations at C-3 have been the types of reactions used.     

A convenient oxazole C-2 protecting group: the synthesis of 4- and 5-substituted oxazoles via metalation of 2-triisopropylsilyloxazoles

[reaction: see text] Metalation of oxazoles at the 4 and 5 position was achieved after regioselective C-2 silyl protection. Removal of the protecting group was then accomplished under mild conditions allowing for a straightforward preparation of C-5 monosubstituted and C-4,5 disubstituted oxazoles. The first practical C-2 protecting group of oxazoles has been demonstrated.     

Amphidinolides T2, T3, and T4, new 19-membered macrolides from the dinoflagellate Amphidinium sp. and the biosynthesis of amphidinolide T1.

Three new 19-membered macrolides, amphidinolides T2 (2), T3 (3), and T4 (4), structurally related to amphidinolide T1 (1) have been isolated from two strains of marine dinoflagellates of the genus Amphidinium. The structures of 2-4 were elucidated on the basis of spectroscopic data. The absolute configurations at C-7, C-8, and C-10 of 1-4 were determined by comparison of NMR data of their C-1-C-12 segments with those of synthetic model compounds for the tetrahydrofuran portion. The biosynthetic origins of amphidinolide T1 (1) were investigated on the basis of 13C NMR data of a 13C enriched sample obtained by feeding experiments with [1-(13)C], [2-(13)C], and [1,2-(13)C2] sodium acetates and 13C-labeled sodium bicarbonate in the cultures of the dinoflagellate. These incorporation patterns suggested that amphidinolide T1 (1) was generated from four successive polyketide chains, an isolated C1 unit formed from C-2 of acetates, and three unusual C2 units derived only from C-2 of acetates. Furthermore, it is noted that five oxygenated carbons of C-1, C-7, C-12, C-13, and C-18 were not derived from the C-1 carbonyl, but from the C-2 methyl of acetates.     

Derivatives and reactions of glutacondialdehyde V : The crystal and molecular structure of 5-hydroxy-trans-2, trans-4-pentadienal acetate. The charge distribution in the glutacondialdehyde anion

The structure of 5-hydroxy-trans-2, trans-4-pentadienal acetate has been determined, using three-dimensional diffractometercollected X-ray data. The compound has the all-trans configuration with the atoms C-1 to C-5 in a plane. The charge distribution in the acetate and in the glutacondialdehyde anion have been calculated using the CNDO/2 approximation. In both compounds higher negative charges were found on carbon atoms C-2 and C-4 than on C-1, C-3 and C-5.     

Synthesis and biological properties of C-2 triazolylinosine derivatives

O(6)-(Benzotriazol-1H-yl)guanosine and its 2'-deoxy analogue are readily converted to the O(6)-allyl derivatives that upon diazotization with t-BuONO and TMS-N(3) yield the C-2 azido derivatives. We have previously analyzed the solvent-dependent azide·tetrazole equilibrium of C-6 azidopurine nucleosides, and in contrast to these, the O(6)-allyl C-2 azido nucleosides appear to exist predominantly in the azido form, relatively independent of solvent polarity. In the presently described cases, the tetrazole appears to be very minor. Consistent with the presence of the azido functionality, each neat C-2 azide displayed a prominent IR band at 2126-2130 cm(-1). A screen of conditions for the ligation of the azido nucleosides with alkynes showed that CuCl in t-BuOH/H(2)O is optimal, yielding C-2 1,2,3-triazolyl nucleosides in 70-82% yields. Removal of the silyl groups with Et(3)N·3HF followed by deallylation with PhSO(2)Na/Pd(PPh(3))(4) gave the C-2 triazolylinosine nucleosides. In a continued demonstration of the versatility of O(6)-(benzotriazol-1H-yl)purine nucleosides, one C-2 triazolylinosine derivative was converted to two adenosine analogues via these intermediates, under mild conditions. Products were desilylated for biological assays. The two C-2 triazolyl adenosine analogues demonstrated pronounced antiproliferative activity in human ovarian and colorectal carcinoma cell cultures. When evaluated for antiviral activity against a broad spectrum of DNA and RNA viruses, some of the C-2 triazolylinosine derivatives showed modest inhibitory activity against cytomegalovirus.     

Syntheses of (R) [4-2H2] 2-Amino-3-Butenoic Acid (Vinylglycine) and (R) [4-2H2, 5-2H3] Methionine

Treatment of (R) methionine sulfoxide with NaOD led to exchange of the C-4 methylene and C-5 methyl protons; exchange of the chiral C-2 proton did not occur. Reducation with mercaptoacetic acid gave (R)-[4-²H₂, 5-²H₃] methionine. The latter was converted into its carbobenzyloxy methyl ester sulfoxide, pyrolysis of which followed by deprotection yielded (R)-[4-²H₂] vinylglcine as the hydrochloride.     

Synthesis of stable isoxazolines by [3+2] cycloaddition of oxaziridines with alkynes

N-Alkyl substituted oxaziridines undergo a [3+2] cycloaddition reaction with a variety of terminal alkynes to give the product isoxazolines, whose stability appears to depend on the electronic properties of the groups on the C-3 and C-5 positions. The presence of an electron withdrawing group on C-5 and/or an electron donating group on C-3 causes isomerization of the isoxazolines to β-amino enones.     

C-2 side chain alkylation of 2-methyl-3-alkylindoles via 3-methoxyindolenines:

3-Methoxyindolenines derived from 2-methyl-3-alkylindoles by bromination-methanolysis undergo base induced alkylations and aldol condensations at the C-2 methyl group. The modified indolenines can be efficiently converted to C-2-sides chain alkylated indoles by reduction with lithium-aluminum hydride or zinc.     

Ring opening of nonactivated 2-(1-aminoalkyl) aziridines: unusual regio- and stereoselective C-2 and C-3 cleavage

We have studied the ring opening of nonactivated amino aziridines 1 by water under acidic conditions. Depending on the acid used, amino aziridines are cleaved at C-3 or C-2 with high regioselectivity, and total stereoselectivity, affording chiral 2,3-diaminoalkan-1-ols 3 or 1,3-diaminoalkan-2-ols 4 in high yield.     

1-(2-Pyridyl)-2-propen-1-ol: a multipurpose reagent in organic synthesis

A peculiar thermal behaviour of hydroxyallylpyridyl derivatives, likely associated to the weak acidity of the ‘picoline-type’ hydrogen atom and responsible for the formation of allyl inversion products, has been reported. The ‘mobility’ of the same hydrogen atom allowed the unprotected title compound to behave regioselectively as C-1, C-2 or C-3 carbon nucleophile depending on the thermal or base-promoted experimental conditions and on the kind of electrophile; moreover, the corresponding Hantzsch-type pyridine tautomer displayed a biomimetic ability to transfer hydrogen to aromatic and heteroaromatic nitro derivatives.     

Unusual endoperoxide isomerizations: a convenient entry into 2-vinyl-2-cyclopentenones from saturated fulvene endoperoxides

An unusual peroxide base-promoted isomerization is uncovered. Saturated endoperoxides derived from fulvenes give rise to 2-vinyl-2-cyclopentenones upon treatment with DBU in CH₂Cl₂ in a one-pot reaction. This methodology is applied to a convenient synthesis of dihydrojasmone. Moreover, functional groups placed on the side chain at C-6 participate in the base-catalyzed isomerizations via conjugate attack at the enone moiety to give 2-cyclopentenones carrying oxygen heterocycles at C-2.     

Regioselective functionalization of 2-(2′-fluorophenyl)-3-cyanopyridine and its cyclization to benzo[h]-1,6-naphthyridines

Benzo[h]-1,6-naphthyridines and 5-ones, selectively functionalized at C-2, C-3, C-5 and C-10, were obtained by alkyllithium-, lithium amide- or potassium hydroxide-induced anionic cyclization of 3-cyano-2-(2-fluorophenyl)pyridine, which was functionalized regioselectively at positions 4, 5, 6, and 6′.     

1H- und 13C-NMR-spektroskopische Untersuchungen zur Ladungsverteilung in substituierten 1,3-Dioxan-2-ylium-Salzen

The ¹H and ¹³C NMR spectra of a series of 1,3-dioxan-2-ylium salts substituted at C-2 and C-4, C-5, C-6 have been measured. The atomic charge distribution in 1,3-dioxan- and 1,3-dioxolan-2-ylium cations has been calculated with the MINDO/3 method, leading to a linear correlation between π-charge and ¹³C chemical shift at C-2. The strong C-21-proton downfield shift is caused by the anisotropic influence of the mesomeric cation system. The conformations of substituted 1,3-dioxan-2-ylium cations are discussed.     

Synthese D'Azotures et de Benzoates de Glycosyle a Partir de Sulfites Cycliques Enc C-1, C-2

The reaction of sugars bearing a cyclic sulfite group on C-1, C-2 with azide or benzoate ions, is strereoselective and gives trans- 1,2 glycosyl azides or glycosyl benzoates with a free hydroxyle at C-2. The reaction is performed under mild conditions and gives excellent yields of glycosyl derivatives.     

Formation of intermolecular hydrogen bonds in light-sensitive crystals of C-2′-(o-oxyphenyl)vinyl-N-p-methylphenyl nitrone,C-2′-(2″-oxy-5″-bromophenyl)vinyl-N-p-methylphenyl nitrone,C-2′-(2″-oxy-5″-bromophenyl)-vinyl-N-phenyl nitrone,and C-2′-(o-oxyphenyl)vinyl-n-methyl nitrone

This paper studies the crystal structure of new substituted light-sensitive azomethine N-oxides (nitrones): C-2′-(o-oxyphenyl)vinyl-N-p-methylphenyl nitrone (1), C-2′-(2″-oxy-5″-bromophenyl)vinyl-N-p-methylphenyl nitrone (2), C-2′-(2″-oxy-5″-bromophenyl)-vinyl-N-phenyl nitrone (3), and C-2′-(o-oxyphenyl)vinyl-N-methyl nitrone (4). In contrast to the compounds studied earlier [1, 2], C-2′-(β-oxy-α-naphthyl)vinyl-N-p-methylphenyl nitrone (5), C-2′-(β-oxy-α-naphthyl)vinyl-N-phenyl nitrone (6), C-2′-(o-oxyphenyl) vinyl-N-phenyl nitrone (7), and C-2′-(o-oxyphenyl)vinyl-N-p-bromophenyl nitrone (8), the nitrones studies in this work have anti-rather than syn-orientations of the nitrone and hydroxyl groups. Due to this spatial arrangement of the proton-donating hydroxyl and proton-accepting nitrone groups, molecules in crystals 1–4 are bonded by intermolecular hydrogen bonds (IHB) to form chains but not centrosymmetric dimeric associates (CDA). Two types of chain arrangements were revealed: “head-to-tail” and “head-to-tail, tail-to-head”. It is shown that the introduction of an alkyl substituent instead of an aryl one at the nitrogen atom of the nitrone group in 4 leads to a change in the geometry of the IHB in the H-associate. It is proven that the hydroxyl proton can undergo an intermolecular O→O transfer in the chain of hydrogen bonds in crystals 1–4, which can give rise to photochemical transformations in these crystals. Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 349–362, March–April, 1996. Translated by L. Smolina     

Photochemically induced [4+2]- versus [3+2]-cycloreversion reaction of hexasubstituted 2,3-diaza-bicyclo[3.1.0]hex-2-enes

Hexasubstituted 2,3-diaza-bicyclo[3.1.0]hex-2-enes containing large substituents at C-4 and C-6 upon irradiation undergo a novel [4+2]cycloreversion reaction leading to 2,3-diazahexatriens besides the normal [3+2]cycloreversion.