Synthetic transformations of higher terpenoids: XX. Synthesis and transformations of diterpene ureido esters

Lossen rearrangement of N-hydroxymaleopimaric acid amide p-toluenesulfonate in the presence of amines in methanol led to the formation of the corresponding diterpene ureido esters with high regio- and stereoselectivity. Treatment of the resulting ureides with phosphoryl chloride gave cyclic amidines via intramolecular ring closure. Substituted hydantoins were obtained by reactions of the ureido esters with glyoxal in acid medium, and their treatment with sodium ethoxide in ethanol afforded compounds of the naphtho[1,2-h]-quinazoline series.     

Synthetic transformations of higher terpenoids: XIV. Synthesis of pyrrololabdanoids from lambertianic acid

Treatment of lambertianic acid methyl ester with lead tetraacetate gave terpenoid 2,5-diacetoxydihydrofuran which reacted with primary amines to yield 3-terpenyl-substituted pyrrol-2(5H)-ones; the reaction with hydrazine led to the corresponding pyridazine derivative. The obtained furanoterpenoids underwent oxidative methoxylation by the action of N-chlorobenzenesulfonamide or N-bromosuccinimide in methanol. 2,5-Dimethoxydihydrofurans thus formed were smoothly converted into 3-substituted furan-2(5H)-one in acid medium. Hydrogenation of 2,5-dimethoxydihydrofurans, followed by treatment with amines, gave 1,3-disubstituted pyrroles.     

Synthetic transformations of higher terpenoids: XVIII. Synthesis of optically active 9,10-anthraquinone derivatives

Retro-Diels-Alder decomposition of dodecahydro-endo-4b,12-ethenochrysene-1,4-diones obtained from a tricyclic diterpenoid, levopimaric acid, gave optically active 5-[2-(6-vinyl-2,6-dimethyl-2-carboxycyclohexyl) ethyl]-7-isopropyl-1,4-naphthoquinones which reacted with silyloxybutadienes to produce the corresponding 6- and 7-hydroxyanthraquinones, 5-furyl-7-hydroxytetrahydroanthraquinones, or 5-furyl-7-oxohexahydroanthraquinones. Condensation of the naphthoquinone derivatives with 5-isopropenyl-2,3-dihydrothiophene 1,1-dioxide resulted in the formation of 6,11-dioxodihydro- and 6,11-dioxohexahydroanthra[2,1-b]thiophene 3,3-dioxides. 6- and 7-Hydroxyanthraquinones were also obtained by reaction of dodecahydro-endo-4b,12-ethenochrysene-1,4-diones with Danishevsky diene, followed by cleavage of the polycyclic adducts. The cycloaddition of 5-[2-(-2-carboxy-2,6-dimethyl-6-vinylcyclohexyl)ethyl]-7-isopropyl-1,4-naphthoquinones in the presence of Lewis acids was characterized by increased regioselectivity.     

Synthetic transformations of higher terpenoids: XXXVI. Synthesis of furanolabdanoid glycoconjugates with a 1,2,3-triazole linker

Procedures have been developed for the synthesis of 16-[(propargyloxy)methyl]- and 7- and 18-(propargyloxy)labda-8(9),13,14-trienes from phlomisoic acid. Copper-catalyzed cycloaddition of the labdanoid alkynes to azido derivatives of α-D-glucose, D-galactose, D-xylose, and L-arabinose afforded the corresponding N-glycosyl-1,2,3-triazole conjugates.     

Synthetic transformations of higher terpenoids: XVI. Synthesis of decahydronaphtho[1,2-g]indoles from lambertianic acid

Oxidative methoxylation of 8,17-isopropylidenedioxy derivative of lambertianic acid methyl ester with N-chlorobenzenesulfonamide in methanol, followed by hydrogenation over Raney nickel, gave rise to a 2,5-dimethoxytetrahydrofuran fragment which was converted into N-substituted pyrrole ring by the action of amines in acetic acid. The subsequent removal of the acetonide protection and periodate cleavage of the diols thus formed resulted in the formation of 17-nor-8-oxo derivatives, and the latter underwent smooth cyclization to decahydronaphtho[1,2-g]indoles in acid medium.     

Synthetic transformations of higher terpenoids: XII. Transformation of lambertianic acid into 14,16-epoxyabietane diterpenoids

Hydroxylation of lambertianic acid with potassium permanganate in alkaline medium afforded 15,16-epoxy-8α,17-dihydroxy-13(16),14-labdadienoic acid which was oxidized with periodic acid to the corresponding 8α-hydroxy aldehyde, and the latter underwent smooth cyclization in acid medium to give diterpenoid of the 14,16-epoxyabietane series.     

Synthetic transformations of higher terpenoids: XIV. Heterocyclization reactions of 15,16,18-ricarboxylabdadiene. New nitrogen-containing diterpenoids

The oxidation of methyl lambertianate with Jones’ reagent formed the corresponding anhydride which reacted with amines to form N-substituted terpenoid maleimides. New maleimides demonstrated high activity and stereoselectivity in the Diels-Alder reaction with cyclopentadiene. The condensation of the diterpenoid anhydride with hydrazines led to the formation of derivatives of 3,6-dioxo-1,2,3,6-tetrahydropyridazines of labdane type.     

Synthetic transformations of higher terpenoids: XXXII. Synthesis of 16-alkenyl-substituted labdatrienes by oxidative coupling of methyl phlomisoate with alkenes

Reactions of methyl phlomisoate with methyl acrylate, phenyl acrylate, methyl vinyl ketone, phenyl vinyl ketone, or N-substituted acrylamides catalyzed by Pd(OAc)₂ in the presence of Cu(OAc)₂, p-benzoquinone in the mixture of propionic acid and acetonitrile proceed regio- and stereoselectively with the formation of (E)-16-vinyl labdatrienoates. The oxidative coupling under these conditions of the methyl phlomisoate with styrene results in a mixture of 15,16-distyryl-, 16-styryl-, and 16-(1-phenylvinyl)-derivatives of furanolabdanoid.     

Synthetic transformations of higher terpenoids: XXIV. Synthesis of cyanoethyl derivatives of lupane triterpenoids and their transformation into 1,2,4-oxadiazoles

Cyanoethylation of lupane triterpenoids was performed. Amide oximes of 3β-O-(2-cyanoethyl)-betulinic acid methyl ester and 3β-O-acetyl-28-O-(2-cyanoethyl)betulin and the corresponding O-[2-(1,2,4-oxadiazol-3-yl)ethyl] lupane derivatives were obtained.     

Synthetic transformations of higher terpenoids: XVII. Intramolecular cyclization of N-furfuryl amides of the labdane series

16-(Benzylaminomethyl)lambertianic acid methyl ester reacts with 2-methylprop-2-enoyl chloride to give unsaturated amide which readily undergoes intramolecular [4 + 2]-cycloaddition with formation of terpenoid derivatives of 10-oxa-3-azatricyclo[5.2.1.0^1,5]decenone. Acetylation of lambertianic acid methyl ester with acetic anhydride occurs preferentially at the 2-position of the furan ring and is accompanied by migration of the exocyclic double bond. Reductive amination of 16-acetyl-15,16-epoxylabda-8(9),13,14-triene and subsequent reaction of the resulting amine with 2-methylprop-2-enoyl chloride give intramolecular cyclization products in high yield without isolation of intermediate furfurylacryloyl derivative. Reactions of methyl 16-(benzylaminomethyl)-15,16-epoxylabda-8(9),13,14- and -8(17),13,14-trien-18-oates with maleic anhydride lead to the formation of the corresponding 10-oxa-3-azatricyclo[5.2.1.0^1,5]dec-8-ene-6-carboxylic acid derivatives as mixtures of diastereoisomers.     

Synthetic transformations of higher terpenoids: XXVIII. Diels-Alder reactions of 16-(trimethylsiloxybutadienyl) labdanoids

15,16-Epoxy-16-(3-trimethylsiloxybuta-1,3-dien-1-yl)labdanoids were synthesized, and their reactions with cyclic dienophiles (1,4-benzoquinone, 1,4-toluquinone, 2-bromo-6-methyl-1,4-benzoquinone, and N-methylmaleimide) were studied. The reactions with unsymmetrically substituted benzoquinones were not selective. Methods for the preparation of hybrid compounds containing furan diterpenoid and substituted naphthoquinone, octahydroisoindoletrione, or hexahydroisoindoledione fragments were proposed.     

Synthetic transformations of higher terpenoids: XXIX. Gold catalyzed cycloisomerization of propargylaminomethyl substituted and propargyloxymethyl substituted furanolabdanoids

16-Propargylaminomethyl substituted and 16-propargyloxymethyl substituted furanolabdanoids were synthesized, which under the action of AuCl₃ in acetonitrile underwent cycloisomerization forming 7-hydroxyisoindolines or 7-hydroxydihydroisobenzofurans substituted by a terpenoid fragment.     

Synthetic transformations of higher terpenoids: XV. Transformations of azlactone derived from 16-formyllambertianic acid methyl ester

Condensation of 16-formyllambertianic acid methyl ester with hippuric acid gave methyl 15,16-epoxy-16-[(4Z)-5-oxo-2-phenyl-4,5-dihydrooxazol-4-ylidenemethyl]labda-8(20),13(16),14-trien-19-oate which underwent ready transformation into 2-benzoylamino-3-(2-furyl)acrylic acid of the labdanoid series. Reactions of the diterpenoid azlactone with amines and α-amino acid esters led to the formation of the corresponding carbamoylvinylbenzamides and N-(2-benzoylaminoacryloyl) amino acid esters, and furylacrylic acid hydrazides were formed in reactions with hydrazines. Cyclization of the N′-phenylhydrazide by the action of 1 M aqueous sodium hydroxide gave the corresponding 1,2,4-triazin-6-one. By treatment of the azlactone with aqueous ammonia on heating, 4-substituted 2-phenyl-4,5-dihydroimidazol-5-one was obtained.     

Synthetic transformations of higher terpenoids: XXII. Reactions of lambertianic acid derivatives with organozinc reagents obtained from ethyl bromoalkanoates

Reactions of 16-cyanomethyllambertianate with organozinc reagents obtained from ethyl esters of α-bromoacetic, α-bromopropionic, and α-bromobutyric acids gave the corresponding enaminoesters, β-ketoesters, and β-hydroxyesters of labdanoids whose yield depended on the reaction conditions and the structure of the α-bromoester. By Reformatsky reaction of 16-formylmethyllambertianate with α-bromoesters of carboxylic acids stereoisomeric β-hydroxyesters of labdanoids were synthesized.     

Synthetic transformations of higher terpenoids: XXV. Cross coupling of phlomisoic acid methyl ester with alkenes in the presence of oxidants

The reaction of phlomisoic acid methyl ester with styrene, catalyzed by Pd(OAc)₂, in the presence of Cu(OAc)₂ and 1,4-benzoquinone in a mixture of propionic acid with diethyl ether gave the corresponding 15,16-distyryl derivative and only traces of 15- and 16-monosubstituted furanolabdanoids. Oxidative coupling of the title compound with methyl acrylate under analogous conditions afforded a mixture of 15-mono-, 16-mono-, and 15,16-dialkenylation products whose ratio changed during the process. The reaction was stereoselective, and the exocyclic double bond in the products had exclusively E configuration.     

Synthetic transformations of higher terpenoids: XIX. Synthesis of 1,7-epoxyisoindolones and 7,9a-epoxythiazolo[2,3-<Emphasis Type="Italic">a</Emphasis>]isoindolones from terpenoids

The reductive amination of methyl 16-formyllambertianate with L-leucine or L-methionine esters resulted in labdanoid furfurylamines whose acylation with maleic anhydride on chlorides of methacrylic or crotonic acids gave the corresponding unsaturated amides that readily entered into the reaction of intramolecular [4+2]-cycloaddition giving the corresponding derivatives of 10-oxa-3-azatricyclo[5.2.1.0^1,5]dec-8-en-4-one. As a result of a sequence of reactions: The amination of methyl 16-formyllambertianate with cystamine, the acylation of the obtained methyl 16-thiazolidinyllambertianate with the above mentioned acid chlorides or with maleic anhydride, and the intramolecular cyclization of the arising furfurylamine we obtained terpenoid derivayives of 7,9a-epoxyhexahydrothiazolo[2,3-a]isoindol-5-one.     

Synthetic transformation of higher terpenoids 31. Synthesis of 1,2,3-triazolyl-containing furan labdanoids and studies of their cytotoxic activity

16-(1-R-1,2,3-Triazol-4-ylethyl)-, 16-(1-R-1,2,3-triazol-4-ylmethoxymethyl)-, and 16-{2-(1-R-1,2,3-triazol-4-yl)-1-[(1-R-1,2,3-triazol-4-ylmethoxy)ethyl]}-substituted derivatives of methyl lambertianate were synthesized by 1,3-cycloaddition of labdanoid alkynes with azides. The compounds obtained possess considerable cytotoxicity toward the human tumor cell lines CEM-13, MT-4, and U-937. The most active compound, methyl 16-(2-{2-[(1-benzyl-1H-1,2,3-triazol-4-yl)acetyl]furan-3-yl}ethyl)lambertianate, was found to inhibit the viability of the tumor cells by 50% (CCID₅₀) in the concentration of 7–12 μmol L^?1.     

Acid-catalyzed transformations of pinane terpenoids. New prospects

The review discusses recent advances in the field of acid-catalyzed intra- and intermolecular transformations of pinane terpenoids and their oxygen-containing derivatives.     

Synthetic transformations of isoquinoline alkaloids. Synthesis of new dihydrothebaine-hydroquinone derivatives

1-Bromo-and 1-iodo-6,14-endo-ethenodihydrothebaine-hydroquinones were obtained. The Heck reactions of these halides with various olefins were studied. Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1206–1214, June, 2007.