Total synthesis of pteridic acids A and B

Pteridic acid A (1) is a spirocyclic octaketide produced by the phytoepiphytic actinomycete Streptomyces hygroscopicus TP-A0451 and possesses potent plant-growth-promoting activity comparable to that of indole-3-acetic acid. The enantioselective total synthesis of this natural product was achieved by employing the Sn(OTf)(2)-mediated Evans aldol reaction and the Fukuyama acetylenic coupling reaction as the key C--C bond-forming steps producing 1 through a 14-step sequence in 22 % overall yield from a known oxazolidinone derivative. MgBr(2)-mediated equilibration of an anomerically favored spirocyclic intermediate used for the synthesis of 1 brought about partial epimerization of the spirocenter to give the corresponding anomerically disfavored epimer, which was converted into pteridic acid B (11-epi-1), another plant-growth promoter of the same microbial origin.     

Rubrenolide, total synthesis and revision of its reported stereochemical structure

In this paper the synthesis of the natural product rubrenolide is presented. Due to an error in the original proposed stereochemical structure of rubrenolide, the synthesis was not straightforward. Application of the photo-induced rearrangement of an appropriate epoxy diazomethyl ketone gave access to the precursor lactone with an ee of 91%. Coupling of this lactone with (4S)-2,2-dimethyl-[1,3]-dioxolane-4-carbaldehyde gave, after some additional steps, the final product that was identical with an authentic sample of the natural product.     

Bidirectional synthesis of montamine analogs

Reported herein is a bidirectional synthesis of symmetric N,N′-diacyl hydrazide compounds closely resembling the alkaloid natural product montamine. In the process, di-tert-butyl hydrazine-1,2-dicarboxylate was smoothly dialkylated with alkyl halides, then Boc deprotected and acylated with an acetate-protected acid chloride derived from ferulic acid. After acetate removal, simple montamine analogs were obtained in excellent overall yields. Fischer indole synthesis with 4-methoxyphenylhydrazine hydrochloride and dihydrofuran provided 5-methoxytryptophol, which was then elaborated to the 1,2-bis(5-methoxyindol-3-yl)hydrazide structure bearing the substitution pattern found in montamine.     

Lewis acid-mediated displacements of alkoxydioxolanes: synthesis of a 1,2-dioxolane natural product

[formula: see text] Addition of electron-rich alkenes to the peroxycarbenium ions derived from Lewis acid-mediated ionization of 3-alkoxy-1,2-dioxolanes provides an efficient route for the synthesis of substituted 1,2-dioxolanes. The methodology is illustrated with a rapid synthesis of a 1,2-dioxolane natural product related to the plakinic acids.     

Non-steroidal antiinflammatory agents. VI. Synthesis of 10-oxo-5H-pyrrolo[1,2-b]isoquinoline-3-acetic Acid,a conformationally restricted analogue of tolmetin

The synthesis of 10-oxo-5H-pyrrolo[1,2-b]isoquinoline-3-acetic acid 4 , a tricyclic analogue of tolmetin which might show significant analgesic-antiinflammatory activity, has been accomplished in four steps. Alkylation of ethyl 2-pyrrolylglyoxylate ( 15 ) with 2-cyanobenzyl bromide afforded derivative 16 , which was transformed by the Huang-Minion reaction into the dicarboxylic acid 6 . Cyclization of this key intermediate to 17 , followed by alkaline hydrolysis, afforded 10-oxo-5H-pyrrolo[1,2–6]isoquinoline-3-acetic acid ( 4 ). Various attempted syntheses of 6 are also discussed.     

Synthesis of the marine alkaloid caulersin

A three-step synthesis of caulersin (3) from indole-2-acetic acid methyl ester and indole-2-carbonyl chloride is described. As the spectral data of the synthetic sample differed from those reported for the natural product, the structure was determined by X-ray crystallography.     

Isolation, synthesis and photochemical properties of almazolone, a new indole alkaloid from a red alga of Senegal

An indole alkaloid bearing an oxazolone ring, christened almazolone, has been isolated from a new collection of Haraldiophyllum sp. from Dakar (Senegal), as an 88:12 mixture of (Z)/(E) stereoisomers. The relative ratio could be modified under controlled photochemical and thermal processes. The product (Z)-3-indolyl-2-(phenyl-propionylamino)-acrylic acid obtained by oxazolone ring opening has also been observed. Its formation has been confirmed by alkaline hydrolysis of (Z)-almazolone available from synthesis, where condensation of indole-3-carboxaldehyde with (3-phenylpropionylamino)-acetic acid represents the key step.     

Synthetic studies on amipurimycin: total synthesis of a thymine nucleoside analogue

Amipurimycin, a member of the complex peptidyl nucleoside family of antibiotics, is a Streptomyces-derived potent antifungal agent. The mechanism of action of amipurimycin, however, remains undetermined. Additionally, there are no reports on the total synthesis or structure-activity relationships (SAR) of this potentially useful bioactive compound. In a study aimed at the total synthesis and SAR studies of this natural product, the present research reports the development of a synthetic route to the central pyranosyl amino acid core of amipurimycin and its further elaboration, culminating in the synthesis of a unique thymine analogue. Utilizing a d-serine-derived dihydroaminopyrone as a strategic building block, the synthesis involves de novo construction of the fully functionalized C-3-branched carbohydrate amino acid core, followed by glycosidic attachment of thymine at C-1, and peptidic linking of the C-6 amine with the 1,2-aminocyclopentane carboxylic acid side chain.     

Identification of the nitrosation reaction products of alkyl esters of 1,2-benzisoxazole-3-acetic acid by chemical and crystallographic methods

The reaction between methyl or ethyl esters of 1, 2-benzisoxazole-3-acetic acid and iso-amyl nitrite is reported. The main product is identified as 4-(2′-hydroxyphenyl)furazan-3-carboxylic acid ( 4 ) by chemical and X-ray crystal structure analyses. The synthesis of esters of E- and Z-α-(hydroxyimino)-1, 2-benzisoxazole-3-acetic acid is also reported.     

An improved synthesis of cyclohexenothioxanthenones

An improved synthesis of cyclohexanothioxanthenones in high yield (70-90%) by treatment of thiosalicylic acid ( 4 ) or 2,2′-dithiosalicylic acid with 1,2,3,4-tetrahydronaphthalene ( 5 ) in the presence of concentrated sulfuric acid or a mixture of 95% sulfuric acid with 27-30% fuming sulfuric acid (in 5:1 to 2:1 v/v ratio) was described. The crude product consisted of three isomers which were isolated and identified. These isomers are 1,2-, 2,3- and 3,4-cyclohexanothioxantenone ( 1, 2 , and 3 ).     

A new synthesis of atanine,khaplofoline and their analogues

A facile synthesis of Atanine, Khaplofoline and their analogues is described. The method involves condensation of an appropriately substituted 2-quinolone-3-acetic acid with isobutryaldehyde, as the starting point.     

First total synthesis of (+)-hyacinthacine A2

The first synthesis of (+)-hyacinthacine A₂ has been achieved in six steps from 2,3,5-tri-O-benzyl-d-arabinofuranose in an overall yield of 11%. The structure of this natural product was thus unambiguously established as (1R,2R,3R,7aR)-1,2-dihydroxy-3-hydroxymethylpyrrolizidine.     

Asymmetric total synthesis and stereochemical elucidation of the antitumor agent PM-94128

[reaction: see text]. PM-94128, a novel depsipeptide antitumor agent, has been synthesized for the first time through a highly stereocontrolled route. The key steps for the synthesis of the dihydroxyamino acid moiety involve a diastereoselective addition of tert-butyl lithiopropiolate to a chiral nitrone and a 2,3-dihydro[1,2]oxazin-6-one dihydroxylation. The synthesis serves to define the relative as well as the absolute configuration of the natural product (bearing five stereogenic centers).     

The synthesis of a new benzothiazine derivative,related to oxicams,synthesized from natural safrole

The synthesis of the new derivatives, 2-methyl-6,7-methylenodioxy-2H-1,2-benzothiazin-3-one-4-(N-phenyl)carboxamide 1,1-dioxide ( 6a ) from natural safrole ( 5 ) is described. The principal feature of this route is brevity and the high overall yield, producing the new analogue in ca. 35% from the natural product.     

Preparation of nitrogen-containing heterocycles using ring-closing metathesis (RCM) and its application to natural product synthesis

Our synthetic study of nitrogen-containing heterocycles using ring-closing metathesis (RCM), such as chiral bicyclic lactams, azacycloundecenes, axially chiral macrolactams, 1,2-dihydroquinolines, 2-quinolinone and indoles, including a development of silyl-enol ether ene metathesis and isomerization of terminal olefins, are described. Their applications to natural product synthesis are also reported.     

Total synthesis of formamicin

The enantioselective total synthesis of the cytotoxic plecomacrolide natural product formamicin (1) is described. Key aspects of this synthesis include the efficient transacetalation reactions of MOM ethers 28 and 38 to form the seven-membered formyl acetals 29 and 39, a late-stage Suzuki cross-coupling reaction of the highly functionalized vinyl boronic acid 6 and vinyl iodide 7, a highly beta-selective glycosidation reaction of beta-hydroxy ketone 4 with 2,6-dideoxy-2-iodoglucopyranosyl fluoride 3, and the global desilylation of penultimate intermediate 77 mediated by in situ generated Et(3)N.2HF.     

Determination of absolute structure of macroviracins by chemical synthesis

The relative and absolute configurations of macroviracins have been established by the stereocontrolled synthesis of methyl ester 2a of the C(22) carboxylic acid, a constitutive fatty acid of macroviracin A (1), and their comparison to a sample 2 derived from the natural product 1. [structure: see text]     

Design, synthesis, and bioactivity of the first nonsteroidal mimetics of brassinolide

Ten novel compounds, each consisting of two subunits and a linker, were designed with the aid of molecular modeling to resemble the natural steroidal phytohormone brassinolide. The mimetics were synthesized and subjected to the rice leaf lamina inclination bioassay to test for brassinosteroid activity. Most of the mimetics displayed very weak or no bioactivity, but two were strongly active when coapplied with the auxin indole-3-acetic acid (IAA), which synergizes the activity of brassinosteroids. Thus, 1-(4,6 alpha,7 alpha-trihydroxy-5,6,7,8-tetrahydronaphthyl)-2-(6 alpha',7 alpha'-dihydroxy-5',6',7',8'-tetrahydronaphthyl)ethyne (4) and (E)-1,2-bis[trans-(4a alpha,8a beta)-4-oxo-6 alpha,7 alpha-dihydroxy-4a,5,6,7,8,8a-hexahydro-(3H)-naphthyl]ethylene (11) showed exceptional activity at doses as low as 0.01 ng and 0.001 ng/plant, respectively. These compounds are the first biologically active nonsteroidal brassinolide mimetics.     

Abietane diterpenoids from the barks of Cryptomeria japonica

From the bark of Cryptomeria japonica were isolated sugikurojins I (1) and J (2), and an abietane derivative (3) was obtained for the first time as a natural product. These structures were elucidated primarily through extensive NMR experiments. Sugikurojin I (1) has a unique skeleton incorporating an abietane diterpene and a 1,10-secocadinane sesquiterpene. Sugikurojin J (2) is a peroxyester of hydroxyabietane diterpene and isopimarane acid diterpene. Compound 3 was p-quinone acid, which occurred by cleavage between C-7 and C-8 of sugiol; it was deduced to [4'-isopropyl-1(S),3,3-trimethyl-3',6'-dioxo-bicyclohexyl-1',4'-dien-2(R)-yl]-acetic acid. Also obtained in this investigation were three known diterpenes (4-6).     

Enantioselective total synthesis of a natural hydrocarbazolone alkaloid,identification of its stereochemistry,and revision of its spectroscopic data

The natural hydrocarbazolone alkaloid (1R,2R,3R)-3-hydroxy-1,2-dimethyl-1,2,3,9-tetrahydro-4H-carbazol-4-one has been synthesized in a catalytic and enantioselective manner. A key hydrocarbazole derivative was constructed by the holmium-catalyzed Diels-Alder reaction of (silyloxyvinyl)indole as the diene. Total synthesis of the natural product clarified the ambiguity in the spectroscopic data reported for natural products.