Synthesis and cytotoxicity evaluation of diastereoisomers and N-terminal analogues of tubulysin-U

Synthesis and Superpotent Anticancer Activity of Tubulysins Carrying Non‐hydrolysable N‐Substituents on Tubuvaline

“…All the tubulysin analogues 24 a – m were tested for their antiproliferative activity on human colon cancer cell line HT‐29 (Table ). These compounds were compared to TubA; TubU, and the N ‐Me tubulysin U derivative Me‐TubU (R=Me, X=H in structure 24 in Table ). All the assayed compounds showed strong cytotoxic activity, with IC 50 values in the p m range (IC 50 <0.28 n m ), which were lower than that of the reference natural tubulysin TubA (IC 50 =0.75 n m ), and significantly lower than those of the synthetic tubulysin derivatives reported so far in the literature (IC 50 values in the order of n m units).…”

“…Total synthesis of modified tubulysins combined with structure–activity relationship (SAR) studies allowed key structural parameters related to tubulysin cytotoxicity to be defined . The Tuv carbon atom stereochemistry as well as the presence of both isopropyl and acetyl groups in the Tup fragment are recognised as the most important features for maximizing cytotoxicity.…”

“…The d ‐configuration of the stereocentre and the Mep N‐alkyl substitution are other sensitive structural parameters. Minor effects on cytotoxicity have been associated instead with N,O‐acetal moiety replacement by carbon chains, thiazole‐ring substitution (although within few tested alternative aromatic or heteroaromatic rings), Tup stereochemistry, and the size of the aza‐cycloalkyl moiety . Moreover, a C 6 H 4 ‐4‐OH instead of a C 6 H 5 residue in the Tup fragment induced a weak cytotoxicity drop, as a likely consequence of an overall lipophilicity decrease …”

“…[1,15] To tal synthesis of modified tubulysins combined with structure-activity relationship (SAR) studies allowed key structural parameters related to tubulysin cytotoxicity to be defined. [9,[21][22][23] The Tuvc arbon atom stereochemistry as wella s the presence of both isopropyl anda cetyl groupsi nt he Tup fragment are recognised as the mosti mportant features for maximizing cytotoxicity.T he d-configuration of the stereocentre and the Mep N-alkyl substitution are other sensitives tructural parameters. Minor effects on cytotoxicity have been asso-ciated insteadw ith N,O-acetal moiety replacement by carbon chains, thiazole-rings ubstitution (although within few tested alternative aromatic or heteroaromatic rings), Tups tereochemistry,a nd the size of the aza-cycloalkyl moiety.…”

“…Minor effects on cytotoxicity have been asso-ciated insteadw ith N,O-acetal moiety replacement by carbon chains, thiazole-rings ubstitution (although within few tested alternative aromatic or heteroaromatic rings), Tups tereochemistry,a nd the size of the aza-cycloalkyl moiety. [9,[21][22][23][24][25] Moreover, aC 6 H 4 -4-OH instead of aC 6 H 5 residue in the Tupf ragment induced aw eak cytotoxicity drop, as al ikely consequence of an overall lipophilicity decrease. [9] Although both naturala nd synthetic tubulysins showed stronga nticancer potential, to our knowledge unconjugated tubulysin derivatives have never been successfully used in vivo, due to their reported extremelyn arrow therapeutic windows.D ef acto, the tubulysin dosage and formulation used so far in in vivo experiments either induceda nimal death or showed no significant therapeutic effect.…”