Synthesis of Cryptothilone 1, the First Cryptophycin−Epothilone Hybrid

A hybrid structure was synthesized in which one portion is characteristic of a cryptophycin and a second sector bears the signature of an epothilone. The hybrid, in contrast to parent cryptophycin and epothilone systems, showed no effect on the tubulin assembly reaction

A Novel Palladium-Mediated Coupling Approach to 2,3-Disubstituted Benzo[<i>b</i>]thiophenes and Its Application to the Synthesis of Tubulin Binding Agents

Flexible, convergent access to 2,3-disubstituted benzo[b]thiophenes has been developed. The most concise approach involves sequential coupling of o-bromoiodobenzenes with benzylmercaptan and zinc acetylides to give benzyl o-ethynylphenyl sulfides which react with iodine to give 3-iodobenzo[b]thiophenes in a 5-endo-dig iodocyclization. These iodides can be further elaborated using palladium-mediated coupling and/or metalation techniques. This method has been applied to the synthesis of some novel tubulin binding agents

One-Pot Synthesis of Benzo[<i>b</i>]furan and Indole Inhibitors of Tubulin Polymerization

Benzo[b]furan and indole analogues of some recently identified benzo[b]thiophene inhibitors of tubulin polymerization have been prepared, and their biological activity has been assessed. Several very potent analogues were identified

A Novel Palladium-Mediated Coupling Approach to 2,3-Disubstituted Benzo[<i>b</i>]thiophenes and Its Application to the Synthesis of Tubulin Binding Agents

Flexible, convergent access to 2,3-disubstituted benzo[b]thiophenes has been developed. The most concise approach involves sequential coupling of o-bromoiodobenzenes with benzylmercaptan and zinc acetylides to give benzyl o-ethynylphenyl sulfides which react with iodine to give 3-iodobenzo[b]thiophenes in a 5-endo-dig iodocyclization. These iodides can be further elaborated using palladium-mediated coupling and/or metalation techniques. This method has been applied to the synthesis of some novel tubulin binding agents

Synthesis and Biological Activities of (<i>R</i>)- and (<i>S</i>)-<i>N</i>-(4-Methoxyphenyl)-<i>N</i>,2,6-trimethyl-6,7-dihydro-5<i>H</i>-cyclopenta[<i>d</i>]pyrimidin-4-aminium Chloride as Potent Cytotoxic Antitubulin Agents

(R,S)-1 is a potent antimitotic compound. (R)-1·HCl and (S)-1·HCl were synthesized from (R)- and (S)-3-methyladipic acid. Both enantiomers were potent inhibitors of cell proliferation and caused cellular microtubule loss and mitotic arrest. They inhibited purified tubulin assembly and the binding of [3H]colchicine to tubulin, with (S)-1 being about twice as potent. Cytotoxicity against 60 tumor cell lines, however, indicated that the (S)-isomer was 10- to 88-fold more potent than the (R)-isomer

Synthesis of Chamaecypanone C Analogues from <i>in Situ</i>-Generated Cyclopentadienones and Their Biological Evaluation

A rhodium-catalyzed dehydrogenation protocol for the conversion of 3,5-diarylcyclopentenones to the corresponding 2,4-diarylcyclopentadienones has been developed. With this protocol, analogues of the cytotoxic agent chamaecypanone C have been synthesized <i>via</i> Diels–Alder cycloaddition between the cyclopentadienones and <i>in situ</i>-generated <i>o</i>-quinols. Biological evaluation of these analogues revealed a compound with higher activity as a microtubule inhibitor and cytotoxic agent in comparison with the parent structure

Synthesis of Chamaecypanone C Analogues from <i>in Situ</i>-Generated Cyclopentadienones and Their Biological Evaluation

A rhodium-catalyzed dehydrogenation protocol for the conversion of 3,5-diarylcyclopentenones to the corresponding 2,4-diarylcyclopentadienones has been developed. With this protocol, analogues of the cytotoxic agent chamaecypanone C have been synthesized <i>via</i> Diels–Alder cycloaddition between the cyclopentadienones and <i>in situ</i>-generated <i>o</i>-quinols. Biological evaluation of these analogues revealed a compound with higher activity as a microtubule inhibitor and cytotoxic agent in comparison with the parent structure

Antineoplastic Agents 440. Asymmetric Synthesis and Evaluation of the Combretastatin A-1 SAR Probes (1<i>S</i>,2<i>S</i>)- and (1<i>R</i>,2<i>R</i>)-1,2-Dihydroxy- 1-(2‘,3‘-dihydroxy-4‘-methoxyphenyl)-2-(3‘ ‘,4‘ ‘,5‘ ‘-trimethoxyphenyl)-ethane^‡

The synthetic (E)-isomer (3b) of natural combretastatin A-1 (1a) isolated from the African bushwillow Combretum caffrum was the focus of chiral hydroxylation (Sharpless) reactions as part of a structure−activity relationship study. The resulting (R,R)- and (S,S,)-diols (6 and 7) and synthetic intermediates were evaluated against a series of cancer cell lines, microorganisms, and tubulin. Chiral diols 6 and 7 showed increased activity against the P-388 murine lymphocytic leukemia cell line with ED50 values of 3.9 and 2.9 μg/mL, respectively, when compared to the precursor (E)-stilbene 3b. In contrast, (E)-stilbene 3b exhibited more potent antibiotic activity than the chiral diols (6 and 7). Both diols, (R,R)-6 and (S,S)-7, displayed less cancer cell growth inhibition and less antibiotic activity than did natural combretastatin A-1 (1a) (P-388 ED50 0.25 μg/mL)

Evolution of the Total Syntheses of Ustiloxin Natural Products and Their Analogues

Ustiloxins A−F are antimitotic heterodetic cyclopeptides containing a 13-membered cyclic core structure with a synthetically challenging chiral tertiary alkyl-aryl ether linkage. The first total synthesis of ustiloxin D was achieved in 31 linear steps using an SNAr reaction. An NOE study of this synthetic product showed that ustiloxin D existed as a single atropisomer. Subsequently, highly concise and convergent syntheses of ustiloxins D and F were developed by utilizing a newly discovered ethynyl aziridine ring-opening reaction in a longest linear sequence of 15 steps. The approach was further optimized to achieve a better macrolactamization strategy. Ustiloxins D, F, and eight analogues (14-MeO-ustiloxin D, four analogues with different amino acid residues at the C-6 position, and three (9R,10S)-epi-ustiloxin analogues) were prepared via the second-generation route. Evaluation of these compounds as inhibitors of tubulin polymerization demonstrated that variation at the C-6 position is tolerated to a certain extent. In contrast, the S configuration of the C-9 methylamino group and a free phenolic hydroxyl group are essential for inhibition of tubulin polymerization

Evolution of the Total Syntheses of Ustiloxin Natural Products and Their Analogues

Ustiloxins A−F are antimitotic heterodetic cyclopeptides containing a 13-membered cyclic core structure with a synthetically challenging chiral tertiary alkyl-aryl ether linkage. The first total synthesis of ustiloxin D was achieved in 31 linear steps using an SNAr reaction. An NOE study of this synthetic product showed that ustiloxin D existed as a single atropisomer. Subsequently, highly concise and convergent syntheses of ustiloxins D and F were developed by utilizing a newly discovered ethynyl aziridine ring-opening reaction in a longest linear sequence of 15 steps. The approach was further optimized to achieve a better macrolactamization strategy. Ustiloxins D, F, and eight analogues (14-MeO-ustiloxin D, four analogues with different amino acid residues at the C-6 position, and three (9R,10S)-epi-ustiloxin analogues) were prepared via the second-generation route. Evaluation of these compounds as inhibitors of tubulin polymerization demonstrated that variation at the C-6 position is tolerated to a certain extent. In contrast, the S configuration of the C-9 methylamino group and a free phenolic hydroxyl group are essential for inhibition of tubulin polymerization