Antineoplastic Agents. 607. Emetine Auristatins

The remarkable biological activity of the dolastatin 10 structural modifications quinstatins and isoquinstatins prompted further investigation into drug hybrids containing biologically active isoquinoline moieties. In this study, the isoquinoline alkaloid emetine was selected as one of the structural domains of a hybrid molecule. That was accomplished by covalently bonding the Dov-Val-Dil-Dap peptide sequence of dolastatin 10 peptide at the N-2' secondary amine of emetine. Three new hybrids were synthesized, 5, 9, and 10. Comparison of the biological activity of these new peptide-emetine analogues with emetine showed complete retention of activity for 5 and a 10-fold decrease for hybrids 9 and 10. The result was surprising, as the activity of emetine is usually lost or greatly reduced when substituted at the N-2' position.

Antineoplastic Agents. 605. Isoquinstatins

In order to further explore quinoline-type structural modification of the powerful anticancer drug dolastatin 10, an Indian Ocean sea hare constituent and parent molecule of the very successful antibody drug conjugate (ADC) Adcetris, our recent quinstatin study has been extended by replacing the quinoline ring with an isoquinoline. The resulting isoquinstatins (4-6) were modified to N-terminal desmethylisoquinstatins (7-9) and, in turn, bonded to appropriate linker units to give linker-desmethylisoquinstatin conjugates 11-13 in preparation for eventual monoclonal antibody attachment. Comparison of the new isoquinstatins with their quinstatin counterparts against six human cancer cell lines indicated the isoquinstatins to have GI₅₀ values that were comparable to or somewhat higher than those of the isomeric quinstatins. However, desmethylisoquinstatin 5 (7) was significantly more potent than its desmethylquinstatin 5 analogue. When evaluated against quinstatin 8, its isoquinstatin 8 (6) counterpart was somewhat less potent. In general, the isoquinstatins evaluated proved to be quite strong cancer cell growth inhibitors.

Antineoplastic Agents. 606. The Betulastatins

The medicinal potential of the plant pentacyclic triterpene betulin has generated long-term interest focused on various SAR research avenues. The present approach was based on producing further analogues (chimeras) arising from a studied modification of betulin bonded to the Dov-Val-Dil-Dap unit of the powerful anticancer drug dolastatin 10, which provided betulastatins 1 (7b), 2 (11b), 3 (16b), and 4 (18b). Betulastatin 1, 2, and 4 exhibited modest levels of cancer cell growth inhibition against six cancer cell lines. Betulastatin 3 proved to be the most potent cancer cell growth inhibitor (GI₅₀ 0.01 μg/mL) and seems worthy of further development, as the presumed mixture of anticancer mechanisms of action may prove to be useful.

Antineoplastic Agents. 604. The Path of Quinstatin Derivatives to Antibody Drug Conjugates

To further evaluate the exceptional cancer cell growth inhibition by the quinstatins, of which one of the series, quinstatin 8, approaches the exceptional cytotoxic activity of the parent dolastatin 10 (1), four of the quinstatins have been converted to desmethyl derivatives. Three of the four (4, 5, and 8 [7b-d]) were next bonded to the linker (8) employed in the synthesis of the very successful and structurally related anticancer drug Adcetris (3). Owing to these structural modifications, a next step could be taken by bonding to a monoclonal antibody, thereby producing an antibody drug conjugate (ADC) related to Adcetris structurally but with the possibility of a wider spectrum of activity and utility.

1.15 PW-850 J compressed beam demonstration using the PETAL facility

The Petawatt Aquitaine Laser (PETAL) facility was designed and constructed by the French Commissariat à l'énergie atomique et aux énergies alternatives (CEA) as an additional PW beamline to the Laser MegaJoule (LMJ) facility. PETAL energy is limited to 1 kJ at the beginning due to the damage threshold of the final optics. In this paper, we present the commissioning of the PW PETAL beamline. The first kJ shots in the amplifier section with a large spectrum front end, the alignment of the synthetic aperture compression stage and the initial demonstration of the 1.15 PW @ 850 J operations in the compression stage are detailed. Issues encountered relating to damage to optics are also addressed.

Antineoplastic Agents. 603. Quinstatins: Exceptional Cancer Cell Growth Inhibitors

Discovery of the exceptionally powerful anticancer drug dolastatin 10 (1), contained in the sea hare Dolabella auricularia, opened a new frontier needed for improving human cancer treatment. Subsequently, major advances have been achieved based on results of structurally modifying this unusual natural peptide while maintaining the remarkable anticancer activity necessary for preparation of successful monoclonal antibody drug conjugates (ADC). Among the first several hundred SAR products based on dolastatin 10 our group synthesized and termed auristatins was auristatin E (2a). An anticancer activity-equivalent, desmethylaurisatin E (2b), linked to a CD30 monoclonal antibody is the very successful anticancer drug Adcetris, now approved for use in 65 countries. In the present investigation, we discovered a new subset of auristatins designated quinstatins derived from dolastatin 10 by replacing the C-terminal Doe unit with a carefully designed quinoline, which led to low or subnanomolar levels of cancer cell growth inhibition required for construction of chemically unique ADC drugs. The synthesis of quinstatins 2-8 is presented along with their cancer cell line biological data.

Isolation and Structure of Cancer Cell Growth Inhibitory Tetracyclic Triterpenoids from the Zimbabwean Monadenium lugardae

The Zimbabwean medicinal plant Monadenium lugardae was evaluated as a potential source of new anticancer constituents. Four new tetracyclic triterpene (1-4) were isolated, accompanied by four previously known triterpenes (5-8). Against a panel of human tumor cell lines, lugardstatins 1 (1) and 2 (2) had good cancer cell growth inhibitory activity. All of the triterpene structures (1-8) were established by 1D and 2D NMR spectrometric and HR mass spectrometric analysis.

Antineoplastic Agents. 585. Isolation of Bridelia ferruginea Anticancer Podophyllotoxins and Synthesis of 4-Aza-podophyllotoxin Structural Modifications

Cytotoxic constituents of the terrestrial plant Bridelia ferruginea were isolated using bioactivity-guided fractionation, which revealed the presence of the previously known deoxypodophyllotoxin (1), isopicrodeoxypodophyllotoxin (2), β-peltatin (3), β-peltatin-5-O-β-D-glucopyranoside (3a), and the indole neoechinulin (4). As an extension of previous podophyllotoxin research, SAR studies were undertaken focused on 4-aza-podophyllotoxin structural modifications. A number of such derivatives were synthesized following modifications to the A and E rings. Such structural modifications with alkyl and 4-fluorobenzyl substituents at the 4-aza position provided the most potent cancer cell growth inhibitory activity (GI50 0.1 to <0.03 μg/mL) against a panel of six human cancer cell lines and one murine cancer cell line. Several compounds corresponding to 4'-demethylated modifications were also synthesized and found to be significantly less potent.

The Cephalostatins. 24. Isolation, Structure, and Cancer Cell Growth Inhibition of Cephalostatin 20

For the purpose of advancing knowledge of the structural variations available in the natural cephalostatins contained in the marine worm Cephalodiscus gilchristi, the isolation and structure of the 20th member (1) has been accomplished (10(-7) % yield). In turn cephalostatin 20 (1) proved to be enough for an initial SAR study comprising six important human cancer cell lines. A parallel objective was aimed at the possible discovery of a natural cephalostatin with a more accessible structure for total synthesis and/or synthetic modifications, but with powerful cancer cell growth inhibition.

The Cephalostatins. 23. Conversion of Hecogenin to a Steroidal 1,6-Dioxaspiro[5.5]nonane Analogue for Cephalostatin 11

Cephalostatin 1 (1) has proved to be a remarkably potent cancer cell growth inhibitor. Since this steroidal alkaloid constituent of the marine worm Cephalodiscus gilchristi possesses a complex structure, providing preclinical supplies by total synthesis continues to be challenging. Therefore, syntheses of less complex structural modifications of this important pyrazine have also received substantial attention. Herein are summarized the synthesis of [5.5]spiroketal 5, a simplified right-side steroidal unit of 1, in seven steps from hecogenin acetate (11) with an overall yield of 4.6%. Consistent with other SAR studies, such reduction in structural complexity compared to 1 led to loss of cancer cell growth inhibitory activity against the P388 lymphocytic leukemia cell line.

Antineoplastic agents. 600. From the South Pacific Ocean to the silstatins

The recent advances in the development of antibody and other drug conjugates for targeted cancer treatment have further increased the need for powerful cancer cell growth inhibitors. Toward that objective we have extended our earlier discovery of the remarkable anticancer bacillistatins 1 and 2 from Bacillus silvestris to SAR and other structural modifications such as availability of a free hydroxy group for antibody-drug conjugate (ADC) and other prodrug linkage. That direction has resulted in seven structural modifications designated silstatins 1-8 (7a, 8a, 8b, 14a, 15a, 15b, 18a, and 18b), where the exceptional cancer cell growth inhibition of some of them are in the range GI50 10(-3)-10(-4) μM/mL. Silstatin 7 (18a) was converted to a glucuronic conjugate (28) that displayed an impressive reduction in toxicity during transport.

Antineoplastic agents. 599. Total synthesis of dolastatin 16

The first 23-step total synthesis of the cyclodepsipeptide dolastatin 16 (1) has been achieved. Synthesis of the dolaphenvaline and dolamethylleuine amino acid units using simplified methods improved the overall efficiency. The formation of the 25-membered macrocycle employing lactonization with 2-methyl-6-nitrobenzoic anhydride completed a key step in the synthesis. Regrettably, the synthetic dolastatin 16 (1), while otherwise identical (by X-ray crystal structure and spectral analyses) with the natural product, did not reproduce the powerful (nanomolar) cancer cell growth inhibition displayed by the natural isolate. Presumably this result can be attributed to conformation(s) of the synthetic dolastatin 16 (1) or to a chemically undetected component isolated with the natural product.

Antineoplastic agents 596. Isolation and structure of chromomycin A5 from a Beaufort Sea microorganism

Isolation and structure of chromomycin A₅ from a Beaufort Sea microorganism.

Antineoplastic agents. 595. Structural modifications of betulin and the X-ray crystal structure of an unusual betulin amine dimer

The lupane-type triterpene betulin (1) has been subjected to a series of structural modifications for the purpose of evaluating resultant cancer cell growth inhibitory activity. The reaction sequence 7→11→12 was especially noteworthy in providing a betulin-derived amine dimer. Other unexpected synthetic results included the 11 and 13/14→17 conversions, which yielded an imidazo derivative. X-ray crystal structures of dimer 12 and intermediate 25 are reported. All of the betulin modifications were examined for anticancer activity against the P388 murine and human cell lines. Significant cancer cell growth inhibition was found for 4, 8, 9, 15/16, 19, 20, 24, and 26, which further defines the utility of the betulin scaffold.

Isolation and structures of axistatins 1-3 from the Republic of Palau marine sponge Agelas axifera Hentschel

An investigation begun in 1979 directed at the Republic of Palau marine sponge Agelas axifera Hentschel for cancer cell growth inhibitory constituents subsequently led to the isolation of three new pyrimidine diterpenes designated axistatins 1 (1), 2 (2), and 3 (3), together with the previously reported formamides 4, 5, and agelasine F (6). The structures were elucidated by analysis of 2D-NMR spectra and by HRMS. All of the isolated compounds were found to be moderate inhibitors of cancer cell growth. Axistatins 1-3 (1-3), formamide 4, and agelasine F (6) also exhibited antimicrobial activity.

Antineoplastic agents. 587. Isolation and structure of 3-epipancratistatin from Narcissus cv. Ice Follies

Bioassay-guided (cancer cell line) separation of an extract prepared from Narcissus cv. Ice Follies (from The Netherlands) led to the isolation of a new Amaryllidaceae isocarbostiryl, 3-epipancratistatin (1b), as well as narciclasine (2). This Narcissus cultivar was found to be a good source of narciclasine. The structure of 1b was established by high-resolution mass and high-field 2D NMR spectroscopic analyses. Against a panel of murine and human cancer cell lines, 3-epipancratistatin (1b) led to cell growth inhibition (GI(50) 2.2-0.69 μg/mL) some 100× less than that found for pancratistatin (1a) and narciclasine (2), thereby revealing an important configurational requirement in 1a for strong cancer cell growth inhibition.

Antineoplastic agents. 548. Synthesis of iodo- and diiodocombstatin phosphate prodrugs

Toward the objective of designing a structurally modified analogue of the combretastatin A-4 phosphate prodrug (1b) with the potential for increased specificity toward thyroid carcinoma, synthesis of a series of iodocombstatin phosphate (11a-h) and diiodocombstatin phosphate prodrugs (12a-h) has been accomplished. The diiodo series was obtained via 8a and 9c from condensation of 4 and 6, and the iodo sequence involved a parallel pathway. Both series of iodocombstatins were found to display significant to powerful inhibition of the growth of a panel of human cancer cell lines and of the murine P388 lymphocytic leukemia cell line. Of the diiodo series, 12a was also found to markedly inhibit growth of pediatric neuroblastoma, and monoiodocombstatin 9a strongly inhibited HUVEC growth. Overall, the strongest activity was found against the breast, CNS, leukemia, lung, and prostate cancer cell lines and the least activity against the pancreas and colon lines. Parallel biological investigations of tubulin interaction, antiangiogenesis, and antimicrobial effects were also conducted.

Synthesis and evaluation of verticipyrone analogues as mitochondrial complex I inhibitors

Verticipyrone has recently been isolated from the culture broth of Verticillium sp. and shown to inhibit NADH fumarate reductase, as well as NADH oxidoreductase (complex I) of the mitochondrial electron transport chain. In order to assess the structural elements in verticipyrone essential for complex I inhibitor, 15 structural analogues were prepared and analyzed for their effects on mitochondrial NADH oxidoreductase and NADH oxidase activities. Also measured were the abilities of several of the analogues to inhibit respiration as judged by a shift to glycolysis, and to inhibit the growth of several mammalian cell lines. The nature of the pyrone ring was shown to be important to potency of inhibition, as was the length and nature of substituents in the side chain of the analogues.

Abstract 4767: Neo-peptides from gene fusions as cancer vaccine antigens

Background: Of all possible sources of antigens for cancer vaccines, frameshift (FS) peptides are attractive in that they may represent neo-antigens. FS peptides may be induced by insertions/deletions or by chimeric transcripts that result from mis-splicing, chromosomal translocations or trans-splicing of mRNA. Aim: In order to discover FS neo-antigens, we have taken a bioinformatical approach at identifying tumor specific, neo-peptides that are generated when chimeric transcripts are translated. Specifically we have focused our attention on identifying chimeric transcripts that create a frameshift when the exons of two different genes are joined. As a result of this gene fusion, approximately 50% of the time a frameshift occurs thus creating a neo-peptide. Method: In order to quickly identify these types of transcripts that are specific to cancer and not present in normal tissue, we have developed an algorithm that can be used to screen publically available databases and high-throughput sequencing data. As proof of principle we have applied this algorithm to the NCBI Expressed Sequence Tag database that contains cDNA sequencing information for normal and cancer tissues. Results: Based on this approach, we have identified and validated 35 chimeric transcripts that are present in breast cancer cell lines and in primary breast tumors. In addition, 9 chimeric transcripts are also present in seven different pancreatic cancer cell lines. Of the 35 chimeric transcripts, 11 chimeric transcripts produce frameshift peptides that are at least nine amino acids or longer and are predicted by SYFPEITHI and Rankpep to be immunogenic and capable of being presented in the most frequent human class I MHC alleles. Moreover, our analyses also identified chimeric transcripts that have already been confirmed by 454 sequencing for breast and prostate cancer. Discussion: Defining the chimeric transcriptome in both healthy and cancer patients could be critical for the development of new therapeutic agents. Of more interest to us, is their potential contribution to a prophylactic cancer vaccine. (This work is supported by a DoD Innovator Award and a Keck Foundation grant to SAJ)

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4767.

Antineoplastic agents. 565. Synthesis of combretastatin D-2 phosphate and dihydro-combretastatin D-2

A modified synthetic route to combretastatin D-2 (5) was devised in order to further evaluate its biological activity, for its conversion to phosphate prodrugs (25-28), and as a route to obtaining dihydro-combretastatin D-2 (42). A parallel first total synthesis of dihydro-combretastatin D-2 was completed, proceeding from a saturated 3-phenylpropionic ester intermediate via the Ullmann biaryl ether reaction (39-41). In contrast to the cancer cell growth inhibitory activity exhibited by combretastatin D-2, relatively minor structural modifications (41, 42) caused elimination of those properties.

Antineoplastic agents. 570. Isolation and structure elucidation of bacillistatins 1 and 2 from a marine Bacillus silvestris

Two new cyclodepsipeptides designated bacillistatins 1 (1) and 2 (2) have been isolated from cultures of a sample of Bacillus silvestris that was obtained from a Pacific Ocean (southern Chile) crab. Each 12-unit cyclodepsipeptide strongly inhibited growth of a human cancer cell line panel, with GI(50)'s of 10(-4)-10(-5) microg/mL, and each compound was active against antibiotic-resistant Streptococcus pneumoniae. The structures were elucidated by a combination of X-ray diffraction and mass and 2D NMR spectroscopic analyses, together with chemical degradation.

Antineoplastic agents. 571. Total synthesis of bacillistatin 2

The first total synthesis of bacillistain 2 (2) has been achieved in 24 steps and 22.9% overall yield, providing a quite efficient route with maximal convergence. Notable features of this approach include two successful applications of the Mitsunobu reaction during respective assemblies of key intermediates 22 and 27, successful employment of 2-methyl-6-nitrobenzoic anhydride (MNBA) in the formation by lactonization of a macrocyclic (36-membered) ring, and very flexible access to structural modifications of the bacillistatin-type cyclodepsipeptides.

Carbohydrate dependent targeting of cancer cells by bleomycin-microbubble conjugates

Biotinylated bleomycin A(5) was attached to streptavidin-derivatized microbubbles, and a solution containing the conjugate was passed over a monolayer of cultured MCF-7 cells. The bleomycin-derivatized microbubbles adhered to the MCF-7 cells, and the association could be monitored by the use of a microscope. Three other cancer cell lines gave similar results. The bleomycin-microbubble conjugate did not bind to a normal breast cell line (MCF-10A) or to the matched noncancer cell lines corresponding to the other cancer cell lines targeted by bleomycin. No binding to any tested cell line was observed when the microbubbles lacked conjugated bleomycin A(5) or when the microbubble contained a bleomycin A(5) analogue lacking the carbohydrate moiety.

Antineoplastic agents. 536. New sources of naturally occurring cancer cell growth inhibitors from marine organisms, terrestrial plants, and microorganisms(1a,)

Bioassay-guided fractionation of extracts of various plants, marine organisms, and microorganisms has led to the discovery of new natural sources of a number of known compounds that have significant biological activity. The isolation of interesting and valuable cancer cell growth inhibitors including majusculamide C ( 1), axinastatin 5 ( 5), bengazoles A ( 6), B ( 7), and E ( 8), manzamine A ( 10), jaspamide ( 11), and neoechinulin A ( 19) has been summarized.

Combretastatin dinitrogen-substituted stilbene analogues as tubulin-binding and vascular-disrupting agents

Several stilbenoid compounds having structural similarity to the combretastatin group of natural products and characterized by the incorporation of two nitrogen-bearing groups (amine, nitro, serinamide) have been prepared by chemical synthesis and evaluated in terms of biochemical and biological activity. The 2',3'-diamino B-ring analogue 17 demonstrated remarkable cytotoxicity against selected human cancer cell lines in vitro (average GI 50 = 13.9 nM) and also showed good activity in regard to inhibition of tubulin assembly (IC 50 = 2.8 microM). In addition, a single dose (10 mg/kg) of compound 17 caused a 40% tumor-selective blood flow shutdown in tumor-bearing SCID mice at 24 h, thus suggesting the potential value of this compound and its corresponding salt formulations as new vascular-disrupting agents.

Antineoplastic agents. 558. Ampelocissus sp. cancer cell growth inhibitory constituents

An investigation of the Phillippine Ampelocissus sp. roots for cancer cell growth inhibitory components led to the isolation of a new acetogenin characterized as 22-epicalamistrin (1) employing primarily 2D NMR and high-resolution mass spectral analysis. Two other antineoplastic constituents proved to be the known acetogenin uvaribonin (2) and chalcone 3. Constituents 1-3 were all found to show significant cancer cell growth inhibitory activity against a panel of human cancer cell lines.

Antineoplastic agents. 560. Isolation and structure of kitastatin 1 from an Alaskan Kitasatospora sp

By utilizing a bioassay-guided separation (P388 lymphocytic leukemia and a panel of human cancer cell lines) of fermentation broths from a Kitasatospora sp. collected from a tundra soil sample taken at the shore of the Beaufort Sea, we have isolated three powerful (GI50 to 0.0006 microg/mL) cancer cell growth inhibitors (1-3) and determined their structures to be closely related cyclodepsipeptides. From 380 L fermentations of Kitasatospora sp. were obtained 2.6 mg of a new cyclodepsipeptide designated kitastatin 1 (3), accompanied by the previously known respirantin (1, 10.8 mg) and its valeryl homologue (2, 4.8 mg). The structures were determined by employment of a series of high-resolution mass and 2D NMR spectroscopic analyses. The stereochemical assignments and overall structures were confirmed by subsequent total synthesis of depsipeptide 1, as reported in the accompanying contribution.

Antineoplastic agents. 550. Synthesis of 10b(s)-epipancratistatin from (+)-narciclasine

By means of a five-step reaction sequence, narciclasine (2a), isolated from Narcissus sp., was converted to 10b(S)-epipancratistatin (3a) in 5.7% overall yield. The key step entailed a radical-initiated 10b,1 C-O cleavage employing tributyltin hydride to yield a B/C cis ring juncture (3b). Biological evaluation of 10b(S)-epipancratistatin (3a) provided evidence that antineoplastic activity was reduced by a factor of 10 when the B/C trans juncture was replaced with a B/C cis ring juncture.

Cyclotrimerization approach to unnatural structural modifications of pancratistatin and other amaryllidaceae constituents — Synthesis and biological evaluation

The phenanthridone core of pancratistatin lacking all aromatic oxygenation was prepared by cyclotrimerization of acetylene-containing scaffolds 30 and 41, reflecting the natural and the C-1 epi configuration, respectively, of the amino inositol moiety. The cobalt-catalyzed formation of the aromatic core led to bisTMS derivatives 39 and 48, as well as bisacetyl derivative 51. The effectiveness of cyclotrimerization of the natural or trans series was compared with that of the cis series. In addition, the yields of cyclotrimerization were compared for propargylic amines and propargylic amides. Eleven derivatives, including the fully hydroxylated phenantridone 39, were tested against seven cancer cell lines. Three of the compounds displayed activities only an order of magnitude less than those of 7-deoxypancratistatin. Full experimental and spectral details are provided for all key compounds and future projections for the preparation of unnatural analogs of Amaryllidaceae constituents are advanced, along with some new insight into the minimum pharmacophore of pancratistatin.Key words: cyclotrimerization, alkaloids, cobalt catalyst.

Antineoplastic agents. 509: synthesis of fluorcombstatin phosphate and related 3-halostilbenes(1)

The present SAR study of combretastatin A-3 (3a) focused on replacement of the 3-hydroxyl group by a series of halogens. That approach with Z-stilbenes resulted in greatly enhanced (>10-100-fold) cancer cell growth inhibition against a panel of human cancer cell lines and the murine P388 lymphocytic leukemia cell line. Synthesis of the 3-fluoro-Z-stilbene designated fluorcombstatin (11a) and its potassium 3'-O-phosphate derivative (16c) by the route 7 --> 8a --> 11a --> 14 --> 16c illustrates the general synthetic pathway. The 3'-O-phosphoric acid ester (15) of 3-bromo-Z-stilbene 13a was also converted to representative cation salts to evaluate the potential for improved aqueous solubility, and the potassium salt (16 mg/mL in water) proved most useful. The fluoro (11a), chloro (12a), and bromo (13a) halocombstatins were nearly equivalent to combretastatin A-4 (1a) as inhibitors of tubulin polymerization and of the binding of colchicine to tubulin. The tubulin binding in cell-free systems was also retained in human umbilical vein endothelial cells. All three halocombstatins retained the powerful human cancer cell line inhibitory activity of combretastatin A-4 (1a) and proved superior to combretastatin A-3 (3a). In addition, the halocombstatins targeted Gram-positive bacteria and Cryptococcus neoformans.

(+)-Phorboxazole A Synthetic Studies. Identification of a Series of Highly Cytotoxic C(45−46) Analogues

[structure: see text] Effective, scalable total syntheses and biological evaluation of six phorboxazole A analogues (1-6) have been achieved. Importantly, the C(45-46)-saturated, C(45-46)-alkenyl, and the C(45-46)-E-chloroalkenyl congeners (4, 5, and 6, respectively) reveal low nanomolar tumor cell growth inhibitory activity (GI50's) similar to or, in some cell lines, greater than that of the phorboxazoles across a diverse panel of human cancer cell lines.

Antineoplastic agents 470. Absolute configuration of the marine sponge bromopyrrole agelastatin A

Two bromopyrrole marine alkaloids were isolated from the Mexican sponge, Agelas sp.: hymenidin (1) and agelastatin A (2). The structures were elucidated by analysis of their spectroscopic data and found to correspond to those in the literature. The absolute configuration of agelastatin A (2) was elucidated by single-crystal X-ray diffraction methods. Agelastatin A (2) exhibited strong activity against a panel of human cancer cell lines as well as human umbilical vein endothelial cells.

Antineoplastic agents. 534. isolation and structure of sansevistatins 1 and 2 from the African Sansevieria ehrenbergii

Using bioactivity-directed isolation procedures, three new spirostanol saponins designated sansevierin A (1), sansevistatin 1 (2), and sansevistatin 2 (3) were isolated (10(-5) % yield) from the CH3OH-CH2Cl2 extract of Sansevieria ehrenbergii, accompanied by three known steroidal saponins (4-6). The structures were determined on the basis of chemical methods and spectroscopic analysis, especially 1D and 2D NMR experiments. Each of the saponins was evaluated against the P388 lymphocytic leukemia cell line and a panel of human cancer cell lines. Except for 1, all were found to cause inhibition of cancer cell growth. In addition, most of the saponins exhibited antimicrobial activity, particularly against the pathogenic fungi Candida albicans and Cryptococcus neoformans.

Antineoplastic agents. 529. Isolation and structure of nootkastatins 1 and 2 from the Alaskan yellow cedar Chamaecyparis nootkatensis

The yellow cedar tree, Chamaecyparis nootkatensis, collected in southeast Alaska was evaluated as a potential source of new anticancer agents. Two new diterpene anticancer constituents termed nootkastatins 1 (4) and 2 (5) were isolated along with three previously known diterpene cancer cell growth inhibitors where two were reported as synthetic modifications of totarol and not previously found in nature. All five diterpene structures were established by HRMS and 1D and 2D NMR spectroscopic analyses combined with three X-ray crystal structure determinations (2, 3, and 5). Against a panel of six human cancer cell lines, this series of diterpenes exhibited inhibition over the range GI(50) 0.75-2.0 microg/mL, and all inhibited the growth of Gram-positive bacteria and fungi.

Antineoplastic Agents. 510. Isolation and structure of dolastatin 19 from the Gulf of California sea hare Dolabella auricularia

The Gulf of California shell-less mollusc Dolabella auricularia has been found to contain a new 14-membered macrocyclic lactone linked to a 2,4-di-O-methyl-l-alpha-rhamnopyranoside, designated dolastatin 19 (1). The new cancer cell growth inhibitor (1, 8.33 x 10(-8)% yield) was obtained by bioassay (P388 lymphocytic leukemia and human cancer cell lines) directed isolation, accompanied by debromoaplysiatoxin (9.17 x 10(-7)% yield) and anhydrodebromoaplysiatoxin (2.0 x 10(-7)% yield). The structures were determined on the basis of analyses of high-resolution mass spectra and high-field NMR data. All the relative stereochemistry for the chiral centers was designated by utilizing NMR techniques.

Antineoplastic agents. 380. Isolation and X-ray crystal structure determination of isoaaptamine from the Republic of Singapore Hymeniacidon sp. and conversion to the phosphate prodrug hystatin 1

By use of bioassay (murine P388 lymphocytic leukemia cell line) guided isolation procedures, extracts of the Republic of Singapore marine sponge Hymeniacidon sp. were found to contain demethyloxyaaptamine (1) and aaptamine (3) as prominent cancer cell growth inhibitory constituents accompanied by the trace, albeit more active, component isoaaptamine (4). The isolation, X-ray structure elucidation, and antineoplastic and antimicrobial activities of isoaaptamine (4) have been summarized. Because of instability, isoaaptamine (4) was converted to a stable sodium phosphate prodrug designated hystatin 1 (7).

Antineoplastic agents. 522. Hernandia peltata (Malaysia) and Hernandia nymphaeifolia (Republic of Maldives)

Bioassay (P388 lymphocytic leukemia cell line and human tumor cell lines)-guided separation of the extracts prepared from the tropical and coastal trees Hernandia peltata (Malaysia) and Hernandianymphaeifolia (Republic of Maldives) led to the isolation of a new lignan designated as hernanol (1) and 12 previously known lignans: (-)-deoxypodophyllotoxin (2), deoxypicropodophyllin (3), (+)-epiaschantin (4), (+)-epieudesmin (5), praderin (6), 5'-methoxyyatein (7), podorhizol (8), deoxypodorhizone (9), bursehernin (10), kusunokinol (11), clusin (12), and (-)-maculatin (13). The oxidative cyclization (with VOF(3)) of lignans 8, 9, and 10 resulted in a new and unusual benzopyran (14), isostegane (15), and a new dibenzocyclooctadiene lactone (16), respectively. The structure and relative stereochemistry of hernanol (1) and lignans 3, 7, 8, 9, 10, 11, and 12 were determined by 1D and 2DNMR and HRMS analyses. The structures and absolute stereochemistry of structures 2, 4, 5, 6, 13, 14, 15, and 16 were unequivocally determined by single-crystal X-ray diffraction analyses. Evaluation against the murine P388 lymphocytic leukemia cell line and human tumor cell lines showed podophyllotoxin derivatives 2 and 3 to be strong cancer cell line growth inhibitors and substances 4, 5, 8, and 15 to have marginal cancer cell line inhibitory activities. Seven of the lignans and one of the synthetic modifications (14) inhibited growth of the pathogenic bacterium Neisseria gonorrhoeae.

Antineoplastic Agents. 520. Isolation and Structure of Irciniastatins A and B from the Indo-Pacific Marine Sponge Ircinia ramosa

The Indo-Pacific marine sponge Ircinia ramosa has been found to contain two powerful (GI50 from 0.001 to <0.0001 microg/mL) murine and human cancer cell growth inhibitors. Both were isolated (10(-3)-10(-4)% yields) by cancer cell line bioassay-guided techniques and named irciniastatins A (1) and B (2). Structural elucidation by a combination of spectral analyses, primarily high resolution mass and 2D-NMR (principally APT, HMQC, HMBC, and ROESY) spectroscopy, revealed the unusual structures 1 and 2.

Isolation and structure of palstatin from the Amazon tree Hymeneae palustris(1)

Bioassay (P388 lymphocytic leukemia cell line and human cancer cell lines) guided separation of an extract prepared from the leaves of Hymenaea palustris Ducké led to the isolation of six cancer cell growth inhibitory flavonoids (1-6). The structures were elucidated by HRMS and 1D and 2D NMR spectral analysis. The new flavonolignan 1 designated palstatin proved to be a methoxy structural modification of 5'-methoxyhydnocarpin-D (2). Flavones 1-4 inhibited growth of the pathogenic bacteria Enterococcus faecalis and/or Neisseria gonorrhoeae.

Antineoplastic agents 460. Synthesis of combretastatin A-2 prodrugs

The original synthesis of combretastatin A-2 (1a) was modified to provide an efficient scale-up procedure for obtaining this antineoplastic stilbene. Subsequent conversion to a useful prodrug was accomplished by phosphorylation employing in situ formation of dibenzylchlorophosphite followed by cleavage of the benzyl ester protective groups with bromotrimethylsilane to afford the phosphoric acid intermediate 11. The latter was immediately treated with sodium methoxide to complete a practical route to the disodium phosphate prodrug (2a). The phosphoric acid precursor (11) of phosphate 2a was employed in a parallel series of reactions to produce a selection of metal and ammonium cation prodrug candidates. Each of the phosphate salts (2a-q) was evaluated with respect to relative solubility behavior, cancer cell growth inhibition and antimicrobial activity.

Antineoplastic agents. 410. Asymmetric hydroxylation of trans-combretastatin A-4

The South African willow tree Combretum caffrum has yielded a number of potent cancer cell growth inhibitors. The present SAR studies of the antineoplastic agent combretastatin A-4 (1c) were focused mainly on the olefinic bridge to determine the effects on cancer cell growth and, potentially, to better define the combretastatin A-4 binding site on tubulin. The geometric trans-isomer 3a of combretastatin A-4 was converted to the (1S,2S)- and (1R,2R)-vicinal diols 4c and 4d, respectively, under Sharpless' asymmetric dihydroxylation conditions. Cancer cell line testing showed the (1S, 2S)-diol 4c to be more potent than its enantiomer 4d. Diol 4c weakly inhibited tubulin polymerization (IC50 = 22 microM, versus 1.2 microM for combretastatin A-4), while 4d was inactive (IC50 > 40 microM). Esterification of either stereoisomer at the diol and/or phenolic positions resulted in elimination of inhibitory activity.

Antineoplastic agents 393. Synthesis of the trans-isomer of combretastatin A-4 prodrug

The (E)-stilbene isomer (2a) of the (Z)-combretastatin A-4 prodrug (1b) was efficiently prepared from (E)-combretastatin A-4 by a reaction sequence employing phosphorylation (dibenzyl chlorophosphite), cleavage (trimethyliodosilane) of the benzyl ester and reaction of the resulting phosphoric acid with sodium methoxide. The sodium phosphate product (2c) was also found to be an important side-product, presumably from iodine-catalyzed isomerization, when the analogous synthetic route was used to obtain the combretastatin A-4 prodrug (1b). The phosphoric acid precursor of prodrug 1b derived from (Z)-combretastatin A-4 (1a) was converted into a series of metal cation and ammonium cation salts to evaluate effects on human cancer cell growth, antimicrobial activities and solubility behavior.

Antineoplastic agents. 397: Isolation and structure of sesterstatins 4 and 5 from Hyrtios erecta (the Republic of Maldives)

The wide ranging marine sponge Hyrtios erecta is the source of the spongistatins, a new class of macrocyclic lactone antineoplastic agents. Continuation of a detailed investigation of cancer cell growth inhibitory (P388 lymphocytic leukemia) fractions (trace) from H. erecta has revealed the presence (10(-5) to 10(-7)% yield) of cytotoxic pentacyclic sesterterpenes. Employing P388 leukemia and human tumor cell line-guided bioassay techniques, two new moderate inhibitors of cancer cells were isolated and named sesterstatins 4 (1a, P388 ED50 4.9 micrograms/mL) and 5 (1b, DU-145 prostate GI50 1.9 micrograms/mL). Similar to other sesterterpenes, sesterstatin 5 inhibited growth of a Gram-positive bacterium. High field (500 MHz) 2-D NMR techniques were primarily employed for initial structural assignments, and structural assignments were confirmed by X-ray crystal structure determination of sesterstatin 4 (1a) and 5 (1b).

Antineoplastic agents 365. Dolastatin 10 SAR probes

The remarkable anticancer drug dolastatin 10 (1a) from the Indian Ocean sea hare Dolabella auricularia is currently undergoing phase I clinical trials. Thirty-eight new structural modifications of this unusual peptide have been synthesized and evaluated against a variety of human and murine cancer cell lines, and for their ability to inhibit tubulin polymerization and vinblastine and GTP binding to tubulin. Dolastatin 10 and one structural modification was found to have antifungal activity, while one other structural modification of the parent compound exhibited antibacterial activity. Some of the new peptides approximated the antineoplastic potency of dolastatin 10, especially those based on replacement of the Doe unit with Met, Phe or an appropriately substituted phenylethylamide.

Synthesis and in vitro cancer cell growth inhibitory activity of monocyclic model compounds containing spongistatin triene side-chains

Two monosaccharides embodying triene side-chains of the spongistatins display significant in vitro activity against human cancer cell lines.

Antineoplastic agents. 362. Isolation and X-ray crystal structure of dibromophakellstatin from the Indian ocean sponge Phakellia mauritiana

Bioassay-guided isolation procedures using human tumor cell lines led to isolation of dibromophakellstatin (4) from the Republic of Seychelles sponge Phakellia mauritiana. The isolation, X-ray crystal structure elucidation, absolute stereochemistry, and antineoplastic activity have been summarized. P. mauritiana was also found to contain dibromophakellin (1), debromohymenialosine (2), thymidine, deoxyuridine, and thymine.