Total syntheses, fragmentation studies, and antitumor/antiproliferative activities of FR901464 and its low picomolar analogue

FR901464 is a potent anticancer natural product that lowers the mRNA levels of oncogenes and tumor suppressor genes. In this article, we report a convergent enantioselective synthesis of FR901464, which was accomplished in 13 linear steps. Central to the synthetic approach was the diene-ene cross olefin metathesis reaction to generate the C6-C7 olefin without the use of protecting groups as the final step. Additional key reactions include a Zr/Ag-promoted alkynylation to set the C4 stereocenter, a mild and chemoselective Red-Al reduction, a reagent-controlled stereoselective Mislow-Evans-type [2,3]-sigmatropic rearrangement to install the C5 stereocenter, a Carreira asymmetric alkynylation to generate the C4' stereocenter, and a highly efficient ring-closing metathesis-allylic oxidation sequence to form an unsaturated lactone. The decomposition pathways of FR901464's right fragment were studied under physiologically relevant conditions. Facile epoxide opening by beta-elimination gave two enones, one of which could undergo dehydration via its hemiketal to form a furan. To prevent this decomposition pathway, a right fragment was rationally designed and synthesized. This analogue was 12 times more stable than the right fragment of the natural product. Using this more stable right fragment analogue, an FR901464 analogue, meayamycin, was prepared in 13 linear steps. The inhibitions of human breast cancer MCF-7 cell proliferation by synthetic FR901464 and meayamycin were studied, and the GI50 values for these compounds were determined to be 1.1 nM and 10 pM, respectively. Thus, meayamycin is among the most potent anticancer small molecules that do not bind to either DNA or microtubule.     

Structural requirements for the antiproliferative activity of pre-mRNA splicing inhibitor FR901464

FR901464, a natural product isolated from a bacterium source, activates a reporter gene, inhibits pre-mRNA splicing, and shows antitumor activity. We previously reported the development of a more potent analogue, meayamycin, through the total synthesis of FR901464. Herein, we report detailed structure-activity relationships of FR901464 that revealed the significance of the epoxide, carbon atoms in the tetrahydropyran ring, the Z geometry of the side chain, the 1,3-diene moiety, the C4-hydroxy group, and the C2'-carbonyl group. Importantly, the methyl group of the acetyl substituent was found to be inessential, leading to a new potent analogue. Additionally, partially based on in vivo data, we synthesized and evaluated potentially more metabolically stable analogues for their antiproliferative activity. These structural insights into FR901464 may contribute to the simplification of the natural product for further drug development.     

Cloning and elucidation of the FR901464 gene cluster revealing a complex acyltransferase-less polyketide synthase using glycerate as starter units

FR901464, an antitumor natural product, represents a new class of potent anticancer small molecules targeting spliceosome and inhibiting both splicing and nuclear retention of pre-mRNA. Herein we describe the biosynthetic gene cluster of FR901464, identified by degenerate primer PCR amplification of a gene encoding the 3-hydroxy-3-methylglutaryl-CoA synthase (HCS) postulated to be involved in the biosynthesis of a β-branched polyketide from Pseudomonas sp. No. 2663. This cluster consists of twenty open reading frames (ORFs) and was localized to 93-kb DNA segment, and its involvement in FR901464 biosynthesis was confirmed by gene inactivation and complementation. FR901464 is biosynthesized by a hybrid polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS), HCS, and acyltransferases (AT)-less system. The PKS/NRPS modules feature unusual domain organization including multiple domain redundancy, inactivation, and tandem. Biochemical characterization of a glyceryl transferase and an acyl carrier protein (ACP) in the start module revealed that it incorporates D-1,3-bisphosphoglycerate, which is dephosphorylated and transferred to ACP as the starter unit. Furthermore, an oxidative Baeyer-Villiger reaction followed by chain release was postulated to form a pyran moiety. On the basis of in silico analysis and genetic and biochemical evidances, a biosynthetic pathway for FR901464 was proposed, which sets the stage to further investigate the complex PKS biochemically and engineer the biosynthetic machinery for the production of novel analogues.     

Development of a flexible strategy towards FR900482 and the mitomycins

FR900482 and the mitomycins are two intriguing classes of alkaloid natural products that have analogous biological mechanisms and obvious structural similarity. Both classes possess potent anticancer activity, a feature that has led to their investigation and implementation for the clinical treatment of human cancer. Given the structural similarity between these natural products, we envisioned a common synthetic strategy by which both classes could be targeted through assembling the mitomycin skeleton prior to further oxidative functionalization. Realization of this strategy with respect to FR900482 was accomplished through the synthesis of 7-epi-FR900482, which displayed equal potency relative to the natural product against two human cancer cell lines. With the challenging goal of a synthesis of either mitomycin or FR900482 in mind, several methodologies were explored. While not all of these methods ultimately proved useful for our synthetic goal, a number of them led to intriguing findings that provide a more complete understanding of several methodologies. In particular, amination via π-allyl palladium complexes for the synthesis of tetrahydroquinolines, eight-membered heterocycle formation via carbonylative lactamization, and amination through late-stage C-H insertion via rhodium catalysis all featured prominently in our synthetic studies.     

Synthesis of a C4-epi-C1-C6 fragment of FR901464 using a novel bromolactolization

[reaction: see text] A synthesis of a C4-epi-C1-C6 fragment of the antitumor agent FR901464 is reported. The advanced intermediate prepared in this study contains two of the three correct stereocenters found in the C1-C6 moiety of FR901464. For the preparation of this intermediate, we have developed a highly diastereoselective bromolactolization of a delta-alkenyl ketone.     

Total Synthesis,Stereochemical Revision,and Biological Assessment of Iriomoteolide-2a

Iriomoteolide-2a is a marine macrolide metabolite isolated from a cultured broth of the benthic dinoflagellate Amphidinium sp. HYA024 strain. This naturally occurring substance was reported to show remarkable cytotoxic activity against human cancer cell lines HeLa and DG-75 and in vivo antitumor activity against murine leukemia P388 cell line. Herein, the total synthesis, stereochemical revision, and biological assessment of iriomoteolide-2a are reported in detail. Total synthesis of the proposed structure 1 of iriomoteolide-2a featured a late-stage convergent assembly of three components by a Suzuki–Miyaura coupling, an esterification, and a ring-closing metathesis. However, the NMR data of synthetic 1 were not identical to those of the natural product. Careful analysis of the NMR data of the authentic material and synthesis/NMR analysis of appropriately designed model compounds led to consideration of four possible stereoisomers 2 – 5 as candidates for the correct structure. Accordingly, total syntheses of 2 – 5 were achieved by taking advantage of the convergent strategy, and comparison of the NMR spectra of synthetic 2 – 5 with those of the natural product led to the conclusion that 5 shows the correct relative configuration of iriomoteolide-2a. The absolute configuration of this natural product was finally established through chiral HPLC analysis of synthetic 5 /ent- 5 with the authentic sample. The antiproliferative activity of the synthetic compounds was assessed against HeLa and A549 cells to show that, in contrast to expectation, synthetic 5 and ent- 5 were only marginally active in these cell lines. This work clearly underscores the vital role of total synthesis in the establishment of the structure and biological activity of natural products.     

Total synthesis of spiruchostatin B aided by an automated synthesizer

The total synthesis of a natural product HDAC inhibitor, spiruchostatin B, was successfully achieved. A 5-step synthesis that included an asymmetric aldol reaction was carried out in an automated synthesizer to provide an (E)-(S)-3-hydroxy-7-thio-4-heptenoic acid segment that is the crucial structure of cysteine-containing, depsipeptidic natural products such as spiruchostatins, FK228, FR901375, and largazole for their inhibitory activity against HDACs.     

Total synthesis of dendroamide A, a novel cyclic peptide that reverses multiple drug resistance

Dendroamide A (1) was isolated from a blue-green alga on the basis of its ability to reverse drug resistance in tumor cells that overexpress either of the transport proteins, P-glycoprotein or MRP1. Because of this activity, methods for the synthesis of analogues of this oxazole- and thiazole-containing cyclic peptide have been developed, and the total synthesis of 1 has been completed. Highlights of the synthetic strategy are as follows: (1) a dicyclohexylcarbodiimide coupling of D-Ala and L-Thr, followed by reaction with Burgess reagent and DBU-assisted oxidation to form D-Ala-oxazole; (2) formation of D-Val-thiazole and D-Ala-thiazole via modified Hantzsch reactions; and (3) use of molecular modeling to select the preferred precursor for the final cyclization of the peptide analogue. Synthetic 1 demonstrated spectral properties identical to those of the natural product and reversed P-glycoprotein-mediated drug resistance more effectively than MRP1-mediated resistance. Certain of the synthetic precursors had biological activity, indicating that cell permeability and peptide cyclization are necessary for optimal activity. Thus, the structure and the biological activities of the natural product are confirmed, and methods for the synthesis of analogues for further structure-activity explorations are defined.     

Total synthesis of FR901464: second generation

FR901464, a potent cell cycle inhibitor, was synthesized in a convergent manner using natural chiral pool, l-threonine, ethyl (S)-lactate and 2-deoxy-d-glucose as starting materials.     

Total synthesis of natural (levo) and enantiomeric (dextro) forms of prostaglandin El

1 newly-discovered method of synthesizing PGE1 (prostaglandin E1) is explained and diagrammed chemically. Recrystallization of the synthetic product produced material identical in all respects with natural PGE1. The synthetic product showed the same infrared spectrum and chromatographic values as racemic and natural forms of PGE1. The biological activity of the synthetic product was found to be .1% of that of the naturally-occurring PGE1 in the stimulation of smooth muscle contraction. This is the 1st report of a total synthesis of PGE1. Research continues on improvements in this synthesizing method and on discovering other synthetic approaches to PGs.     

桉烷-4(15)-烯-1β,7α-二醇的不对称全合成

天然产物桉烷-4(15)-烯-1β,7α-二醇(Y019)从植物中间锦鸡儿中分离得到,初步的药理活性研究中发现具有抗稻瘟霉活性.我们从原料1,3-环己二酮出发以线性步骤11步反应9.4%的总产率,首次完成了天然产物桉烷-4(15)-烯-1β,7α-二醇的不对称全合成,为进一步的药理活性研究奠定了基础.     

Diastereoselective one-pot Wittig olefination-Michael addition and olefin cross metathesis strategy for total synthesis of cytotoxic natural product (+)-varitriol and its higher analogues

A stereoselective route for the total synthesis of anticancer marine natural product (+)-varitriol (1) is detailed herein. The impressive biological activity and interesting structural features of natural (+)-varitriol fuelled us to undertake the synthesis of some higher analogues (1a-j) of this molecule. The key features of the synthetic strategy include one-pot Wittig olefination followed by a highly diastereoselective oxa-Michael addition to assemble stereochemically pure tetrasubstituted THF moiety of the natural varitriol and olefin cross metathesis to couple the aromatic part with tetrasubstituted THF moiety. The total synthesis of title natural product is efficient with 21.8% overall yield for 9 linear steps from D-ribose and thus facilitates the more scaled-up practical route for the synthesis of 1 and its analogues as well. The synthetic (+)-varitriol (1) and its analogues were screened for their cytotoxicity. The present synthetic approach paves the way for preparation of numerous analogues of the title natural product for drug development.     

Total synthesis and biological evaluation of the protein phosphatase 2A inhibitor cytostatin and analogues

The total synthesis of the natural product cytostatin is described which inhibits protein phosphatase 2A. Cytostatin has anti-metastatic properties and induces apoptosis. On the basis of this synthesis the relative and absolute configuration of cytostatin could be assigned. Key structural elements of cytostatin are an alpha,beta-unsaturated lactone group and a side chain embodying a phosphate and a rather unstable (Z,Z,E)-triene subunit. In addition, the natural product carries six stereocenters. For the construction of the stereocenters reagent-controlled transformations were used in order to ensure maximum stereochemical flexibility. The Evans syn-aldol reaction was chosen to establish the stereochemistry at C-4, C-5, C-9 and C-10; C-6 was introduced by means of the Evans asymmetric alkylation. In all cases the same chiral auxiliary was employed as stereodirecting group. The stereocenter at C-11 was established by an asymmetric reduction using CBS-oxazaborolidine. Temporary protection of the phosphate group was achieved best by using the base-labile 9-fluorenylmethyl group, which could be cleanly cleaved by an excess of triethylamine; this reaction yielded analytically pure phosphates after a simple aqueous work-up. The (Z,Z,E)-triene embodied in cytostatin was synthesized by means of a Stille coupling as key transformation. The synthesis sequence established in this way readily gave access to a series of analogues with simplified structure. Initial biological testing of these analogues proved that the alpha,beta-unsaturated lactone, the C-11-hydroxy group and a fully deprotected phosphate moiety at C-9 are essential for the PP2A-inhibitory activity of cytostatin. The rather unstable triene moiety in the side chain can be replaced by other lipophilic residues with only moderate decrease of biological activity. Other phosphatases, that is, PP1, VHR, PTP1B, CD45, were not inhibited by cytostatin or any of the analogues, demonstrating the high selectivity of this compound. These findings will be useful for the design and synthesis of cytostatin-derived chemical tools for the study of biological processes influenced by PP2A.     

Palladium-catalyzed asymmetric allylic substitution of 2-arylcyclohexenol derivatives: asymmetric total syntheses of (+)-crinamine, (-)-haemanthidine, and (+)-pretazettine

Much interest has been shown in Amaryllidaceae alkaloids as synthetic targets due to their wide range of biological activities. Over 100 alkaloids have been isolated from members of the Amaryllidaceae family; most of them can be classified into eight skeletally homogeneous groups. We have succeeded in the first asymmetric total syntheses of the crinane-type alkaloids (+)-crinamine (1), (-)-haemanthidine (2), and (+)-pretazettine (3). The starting cyclohexenylamine 14 was obtained from allyl phosphonate 11c by palladium-catalyzed asymmetric amination in 82% yield and with 74% ee. The product was recrystallized from MeOH. Interestingly, (-)-14 with 99% ee was obtained from the mother liquor (74% recovery). Intramolecular carbonyl-ene reaction of (-)-10 proceeds in a highly stereoselective manner to give hexahydroindole derivative 9 as the sole product. In the Lewis-acid-catalyzed carbonyl-ene reaction, an interesting rearrangement product, 20, was isolated in high yield. From 9, (+)-crinamine was synthesized. Thus, the asymmetric total synthesis of (+)-crinamine was achieved in 10 steps from 11c, and the overall yield is 19%. The total synthesis of (-)-haemanthidine was also achieved from 9 by a short sequence of steps.     

Synthesis of naturally occurring polyynes

Over the past fifty years, hundreds of polyyne compounds have been isolated from nature. These often unstable molecules are found in sources as common as garden vegetables and as obscure as bacterial cultures. Naturally occurring polyynes feature a wide range of structural diversity and display an equally broad array of biological properties. Early synthetic efforts relied primarily on Cu-catalyzed, oxidative acetylenic homo- and heterocoupling reactions to assemble the polyyne framework. The past 25 years, however, have witnessed a renaissance in the field of polyyne natural product synthesis: transition-metal-catalyzed alkynylation reactions and asymmetric transformations have combined to substantially expand access to natural polyynes. This Review recounts these synthetic achievements and also highlights both the natural source(s) and biological relevance for many of these compounds.     

Synthesis of Hemigossypol and its Derivatives

Hemigossypol (3), a sesquiterpene natural product, was previously isolated from Gossypium barbadense and was shown to display improved anti-fungal activity compared to gossypol (1), the disesquiterpene dimer of hemigossypol (3). Gossypol exhibits multiple biological activities. In order to study whether hemigossypol and its derivatives retain the various bioactivities of gossypol, we developed a short and convenient synthetic scheme to synthesize hemigossypol. This is the first de novo synthesis of this natural product. In addition derivatives of hemigossypol with various 2,5-alkyl substituents were synthesized. Modification of the synthetic scheme also afforded the natural product hemigossylic lactone (4) and its 2,5-substituted derivatives.     

(-)-(1R,2S)-肉豆蔻木脂素的不对称合成

报道了天然产物(-)-肉豆蔻木脂素的全合成. 以香草醛为起始原料, 经Wittig反应、LiAlH₄还原和Sharplass不对称双羟化等反应构建了苏式结构的中间体; 以焦性没食子酸为原料, 经Claisen重排反应制得另一种苯丙素片段; 2个中间体通过Mitsunobu反应, 缩合并使构型翻转, 得到赤式-(-)-肉豆蔻木脂素. 为赤式8-O-4′新木脂素的合成提供了一种新方法.     

Stereoselective Synthesis of the Proposed C79–C104 Fragment of Symbiodinolide

Stereoselective and streamlined synthesis of the proposed C79–C104 fragment 2 of symbiodinolide ( 1 ), a polyol marine natural product with a molecular weight of 2860, was achieved. In the synthetic route, the proposed C79–C104 fragment 2 was synthesized by utilizing a Julia–Kocienski olefination and subsequent Sharpless asymmetric dihydroxylation as key transformations in a convergent manner. Detailed comparison of the ¹³C NMR chemical shifts between the natural product and the synthetic C79–C104 fragment 2 revealed that the stereostructure at the C91–C99 carbon chain moiety of symbiodinolide ( 1 ) should be reinvestigated.     

A short and efficient asymmetric synthesis of komaroviquinone

An asymmetric total synthesis of komaroviquinone (1), which is a natural product isolated from Dracocephalum komarovi and shows novel potent trypanocidal activity, was achieved in five steps from the known starting materials. The synthetic route is shorter and more efficient than the reported methods and also useful for the scale-up synthesis.