A modular synthesis of annonaceous acetogenins

A synthesis of four Annonaceous acetogenins, asiminocin, asimicin, asimin, and bullanin, by a modular approach from seven fundamental subunits, A-G, is described. The approach employs a central core aldehyde segment, C, to which are appended an aliphatic terminus, A or B, a spacer subunit, D or E, and a butenolide terminus, F or G. Coupling of the A, B, D, and E segments to the core aldehyde unit is effected by highly diastereoselective additions of enantiopure allylic indium or tin reagents. The butenolide termini are attached to the ACD, BCE, or BCD intermediates by means of a Sonogashira coupling. The design of the core, spacer, and termini subunits is such that any of the C30, C10, or C4 natural acetogenins or stereoisomers thereof could be prepared. IC50 values for the four aforementioned acetogenins against H-116 human colon cancer cells were found to be in the 10(-3) to 10(-4) microM range. The IC90 activities were ca. 10(-3) microM for asimicin and asimin but only 0.1-1 microM for bullanin and asiminocin.     

Mimicry of annonaceous acetogenins: enantioselective synthesis of a (4R)-hydroxy analogue having potent antitumor activity

The (4R)-hydroxylated analogues of annonaceous acetogenin mimicking compound 2 were designed and synthesized structurally on the basis of the naturally occurring annonaceous acetogenin bullatacin, which was discovered as a typical member of the novel family of polyketides with potent cytotoxicity, antitumoral, and other biological activities. The preliminary screenings show that the IC(50) values of 2 were 1.6 x 10(-3) and 8 x 10(-2) microg/mL against HT-29 and HCT-8, respectively. A remarkable enhancement effect was observed by the activity comparison of 1c and its (4R)-hydroxylated analogue 2.     

Systematic synthesis of Bis-THF ring cores in annonaceous acetogenins

Systematic synthesis of bis-THF ring cores, synthetic intermediates of adjacent bis-THF annonaceous acetogenins, has been achieved by asymmetric alkynylation and subsequent stereodivergent THF ring formation. The asymmetric alkynylation of alpha-tetrahydrofuranic aldehyde with (S)-3-butyne-1,2-diol derivatives gave good yields of erythro- and threo-adducts with very high diastereoselectivity. These adducts were converted into four types of bis-THF cores via two kinds of one-pot THF ring formation. [reaction: see text]     

Stereodivergent and reiterative synthesis of bistetrahydrofuran ring cores of annonaceous acetogenins

Eight diastereoisomers of the bistetrahydrofuran ring cores of annonaceous acetogenins have been synthesized by asymmetric alkynylation of alpha-tetrahydrofuranic aldehydes and stereodivergent one-pot tetrahydrofuran (THF) ring formation. In all cases, the asymmetric alkynylation proceeded with very high diastereoselectivity to give eight kinds of optically pure THF cores. We also describe a comparison of the (1)H and (13)C NMR spectral data of the eight isomers and give full details of the THF ring construction.     

The first total synthesis of annonacin, the most typical monotetrahydrofuran annonaceous acetogenins

The first total synthesis of annonacin (1) was achieved by a highly convergent synthetic strategy. All the stereogenic centers were derived from three natural hydroxy acids respectively, except that those at C19 and C20 were produced from a Sharpless AD reaction.     

A bidirectional approach to the synthesis of a complete library of adjacent-bis-THF annonaceous acetogenins

Thirty-six stereoisomers of bifunctional adjacent bis-THF (tetrahydrofuran) lactones have been synthesized, which can afford a complete library of the adjacent bis-THF Annonaceous acetogenins. The bis-THF lactones were synthesized, starting from the enantioselectively pure 8,9:12,13-(E,E and Z,E)-16-benzyloxy-5-hydroxy-hexadeca-1,4-olide, in a highly distereoselective manner using oxidative reactions, including rhenium(VII) oxides-mediated oxidative cyclization, Shi's asymmetric epoxidation, and Sharpless asymmetric dihydroxylation reactions. Using the nonsymmetrical bis-THF lactones, syntheses of two nonnatural acetogenins were achieved.     

阿蒂莫耶番荔枝内酯的研究

本文首次报道从阿蒂莫耶番荔枝(Annona atemoya Hort)种子中分离到七个白色蜡状固体, 经光谱鉴定, 它们分别为已知的抗肿瘤活性番荔枝内酯(annonaceous acetogenin)-Asimicin, Motrilin, Isodesacetyluvaricin,Cherimolin-1, Almunequin, Squamocin-K和Neoannonin。     

Four cytotoxic annonaceous acetogenins from the seeds of Annona squamosa

Four new annonaceous acetogenins (ACGs), squamocin-I (1), II (2) and III (3) and squamoxinone-D (4), together with seven known ACGs (5–11), were isolated from the seeds of Annona squamosa. The structures of all isolates were elucidated and characterised by spectral and chemical methods. Compounds 1–4 were evaluated for their cytotoxicities against Hep G2, SMMC 7721, BEL 7402, BGC 803 and H460 human cancer cell lines. Compound 1 exhibited better potent activity than the positive compound and compound 3 shows selectively cytotoxical activity against H460 with IC₅₀ values of 0.0492 μg/ml.     

Divergence en route to nonclassical annonaceous acetogenins. Synthesis of pyranicin and pyragonicin

Syntheses of the nonclassical annonaceous acetogenins, pyranicin, and pyragonicin from common late-stage intermediates are presented. The construction of key elements relies on asymmetric HWE reactions, including the desymmetrization of a meso-dialdehyde and a parallel kinetic resolution of a racemic aldehyde. A stereoconvergent Pd-catalyzed substitution serves to install the C4 stereocenter in protected form with different orthogonal protective groups. A divergent strategy to form 1,4- and 1,6-diols, employing stereoselective Zn-mediated alkynylations, is used for completion of the core structures. Notably, the stereoselective coupling reaction toward pyragonicin proceeds with highly functionalized fragments. The methodology is further expanded by a divergent synthesis of all stereoisomers of the 2,3,6-trisubstituted tetrahydropyran subunit.     

3 + 2]-annulation reactions of chiral allylsilanes and chiral aldehydes. studies on the synthesis of bis-tetrahydrofuran substructures of annonaceous acetogenins

[Structure: See text] Double asymmetric [3 + 2]-annulation reactions of chiral beta-silyloxyallylsilanes with chiral 2-tetrahydrofuranyl carboxaldehydes have been studied, leading to the stereocontrolled synthesis of six diastereomeric bis-tetrahydrofuran structures corresponding to the core subunits of members of the Annonaceous acetogenin family of natural products. Transition-state models are proposed to account for the stereoselectivity of the double-stereodifferentiating [3 + 2]-annulation reactions.     

Stereochemically general approach to adjacent bis(tetrahydrofuran) cores of annonaceous acetogenins

A series of six 2,5-disubstituted adjacent bis(tetrahydrofuran) stereoisomers with trans/erythro/cis, trans/threo/trans, or cis/threo/cis relative stereochemistry have been synthesized from known dihydroxycyclooctenes via ring opening/cross metathesis and Pd(0)-mediated asymmetric double cycloetherification. The stereochemistry of four of these isomers has been found in the biologically active annonaceous acetogenin natural products. [reaction: see text].     

RuO4-mediated oxidative polycyclization of linear polyenes. A new approach to the synthesis of the bis-THF diol core of antitumour cis-cis adjacent bis-THF annonaceous acetogenins

The RuO₄-catalyzed oxidative polycyclization of some selected linear polyenes, possessing a repetitive 1,5-diene structural motif, has been investigated. The all-trans triene (E,E,E)-acetic acid henicosa-2,6,10-trienyl ester gave the expected bis-tetrahydrofuranyl diol product possessing a threo-cis-threo-cis-threo relative configuration, along with a mixture of the corresponding bis-THF ketols. These compounds can be seen as useful intermediates in the synthesis of the bis-THF diol core of adjacent bis-THF antitumour acetogenins possessing a threo-cis-threo-cis-erythro relative configuration, such as rolliniastatiin-1, membranacin, rollimembrin and membrarollin. Oxidation of the related all-trans tetraene (E,E,E,E)-acetic acid pentacosa-2,6,10,14-tetraenyl ester stops at the second cyclization step giving a mixture of a threo-cis-threo-cis-threo bis-THF diol and the corresponding ketol products. Oxidation of the triene (E,Z,E)-acetic acid 12-acetoxy-dodeca-2,6,10-trienyl ester stops at the monocyclization level failing to give bis-cyclized products, as previously observed for the related isoprenoid triene (E,Z)-farnesyl acetate. This result confirms the difficulty of closing a second THF ring when the central double bond of the triene possesses a cis configuration. Based on the collected results, a plausible model is proposed that both explains the observed cis/trans stereoselectivity for each ring-closing step in these processes, and rationalize the stereochemical course of the previously studied polycyclization of the isoprenoid polyenes (E,E)-farnesyl acetate, geranylgeranyl acetate and squalene.     

An outside-in approach to adjacent bistetrahydrofuran annonaceous acetogenins with C2 core symmetry. Total synthesis of asimicin and a C32 analogue

[reaction: see text] A synthesis of the Annonaceous acetogenin asimicin and a side-chain analogue has been achieved by a highly convergent route in which Grubbs cross-metathesis plays a key role.     

Systematic construction of a monotetrahydrofuran-ring library in annonaceous acetogenins by asymmetric alkynylation and stereodivergent tetrahydrofuran-ring formation

All eight diastereoisomers of the monotetrahydrofuran-ring cores of annonaceous acetogenins have been synthesized through utilization of asymmetric alkynylation and stereodivergent one-pot tetrahydrofuran-ring formation. In all cases, the asymmetric alkynylation proceeded with very high diastereoselectivity to give eight kinds of optically pure tetrahydrofuran core from a common alpha-oxyaldehyde. We also describe a comparison of the (1)H NMR, (13)C NMR, and CD spectral data of the eight isomers and give full details of the tetrahydrofuran-ring construction including a model study of asymmetric alkynylation.     

Enantioselective synthesis of trans-4-methylpipecolic acid

An asymmetric synthesis for the preparation of both enantiomers of trans-methylpipecolic acids is described. It is based on Sharpless epoxidation as a chirality source, regioselective ring opening with allylamine, and ring-closing metathesis to construct the piperidine ring. The stereogenic center at C-4 is set by stereoselective hydrogenation that is directed by the alcohol functionality of an intermediate and proceeds with good diastereomeric control (trans/cis 16/1). Crystallization of the Boc-protected amino acid afforded the target products with excellent chemical (98% de) and enantiomeric purity (99% ee).     

Enantioselective synthesis of (+)-gossonorol and related systems using organozinc reagents

The sesquiterpene (+)-gossonorol is prepared in only three synthetic steps in 60% overall yield and 82% ee from commercially available reagents. The key asymmetric step is the catalytic enantioselective addition of dimethylzinc to 5-methyl-1-(2-methylphenyl)hex-4-en-1-one catalyzed by chiral isoborneolsulfonamide ligands in the presence of titanium tetraisopropoxide. The modular approach allows the synthesis not only of the aforementioned natural product but also other products arising from the corresponding processes of ethylation, phenylation, and ethynylation, just by changing the final nucleophilic reagent and using the same isoborneol type ligand.