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Total synthesis and evaluation of a key series of C5-substituted vinblastine derivatives.

ABSTRACT: A remarkably concise seven- to eight-step total synthesis of a systematic series of key vinblastine derivatives is detailed and used to characterize the importance and probe the role of the C5 ethyl substituent (R = H, Me, Pr, CH=CH(2), C[triple bond]CH, CH(2)OH, and CHO vs Et). The analogues, which bear deep-seated structural changes accessible only by total synthesis, were prepared using a powerful intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles ideally suited for use in the assemblage of the vindoline-derived lower subunit followed by their incorporation into the vinblastine analogues through the use of a single-step biomimetic coupling with catharanthine. The evaluation of the series revealed that the tubulin binding site surrounding this C5 substituent is exquisitely sensitive to the presence (Et > H, 10-fold), size (Me < or = Et > Pr, 10-fold), shape (Et > CH=CH(2) and C[triple bond]CH, > 4-fold), and polarity (Et > CHO > CH(2)OH, >10-20-fold) of this substituent and that on selected occasions only a C5 methyl group may provide analogues that approach the activity observed with the naturally occurring C5 ethyl group.

SUBMITTER: Va P

PROVIDER: S-EPMC2903230 | biostudies-literature | 2010 Jun

REPOSITORIES: biostudies-literature

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Total synthesis and evaluation of a key series of C5-substituted vinblastine derivatives.

Va Porino P Campbell Erica L EL Robertson William M WM Boger Dale L DL

Journal of the American Chemical Society 20100601 24

A remarkably concise seven- to eight-step total synthesis of a systematic series of key vinblastine derivatives is detailed and used to characterize the importance and probe the role of the C5 ethyl substituent (R = H, Me, Pr, CH=CH(2), C[triple bond]CH, CH(2)OH, and CHO vs Et). The analogues, which bear deep-seated structural changes accessible only by total synthesis, were prepared using a powerful intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles ideally suited for use ...[more]

PMID: 20518465

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Project description:Full details of the development of a direct coupling of catharanthine with vindoline to provide vinblastine are described along with key mechanistic and labeling studies. Following an Fe(III)-promoted coupling reaction initiated by generation of a presumed catharanthine radical cation that undergoes a subsequent oxidative fragmentation and diastereoselective coupling with vindoline, addition of the resulting reaction mixture to an Fe(III)-NaBH(4)/air solution leads to oxidation of the C15'-C20' double bond and reduction of the intermediate iminium ion directly providing vinblastine (40-43%) and leurosidine (20-23%), its naturally occurring C20' alcohol isomer. The yield of coupled products, which exclusively possess the natural C16' stereochemistry, approaches or exceeds 80% and the combined yield of the isomeric C20' alcohols is >60%. Preliminary studies of Fe(III)-NaBH(4)/air oxidation reaction illustrate a generalizable trisubstituted olefin scope, identify alternatives to O(2) trap at the oxidized carbon, provide a unique entry into C20' functionalized vinblastines, and afford initial insights into the observed C20' diastereoselectivity. The first disclosure of the use of exo-catharanthine proceeding through Delta(19',20')-anhydrovinblastine in such coupling reactions is also detailed with identical stereochemical consequences. Incorporating either a catharanthine N-methyl group or a vindoline N-formyl group precludes Fe(III)-promoted coupling, whereas the removal of the potentially key C16 methoxy group of vindoline does not adversely impact the coupling efficiency. Extension of these studies provided a total synthesis of vincristine (2) via N-desmethylvinblastine (36, also a natural product), 16-desmethoxyvinblastine (44) and 4-desacetoxy-16-desmethoxyvinblastine (47) both of which we can now suggest are likely natural products produced by C. roseus, desacetylvinblastine (62) and 4-desacetoxyvinblastine (59), as well as a series of key analogues bearing systematic modifications in the vindoline subunit. Their biological evaluation provided additional insights into the key functionality within the vindoline subunit contributing to the activity and sets the foundation on which further, more deep-seated changes in the structures of 1 and 2 will be explored in future studies.

Dataset Information

Total synthesis and evaluation of a key series of C5-substituted vinblastine derivatives.

Publications

Total synthesis and evaluation of a key series of C5-substituted vinblastine derivatives.

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