The influence of natural products upon drug discovery.

Natural products to drugs: natural product derived compounds in clinical trials

Natural products have been the mainstay of cancer chemotherapy for the past 30 years. However, the quickening pace of (aberrant) gene identification, and the new technologies of combinatorial chemistry and high-throughput screening, should provide access to a wide range of new, totally synthetic drugs. Will these new approaches sound the death knell for therapies based on natural products? In reality, natural products are likely to provide many of the lead structures, and these will be used as templates for the construction of novel compounds with enhanced biological properties.

Natural products in cancer chemotherapy: past, present and future

http://www.cornellpharmacology.org/faculty/labs/giannakakou/documents/KowalskiRJetal.JBiolChem.1997.pdf

Activities of the Microtubule-stabilizing Agents Epothilones A and B with Purified Tubulin and in Cells Resistant to Paclitaxel (Taxol®)

Microtubules are dynamic polymers that play crucial roles in a large number of cellular functions Their pivotal role in mitosis makes them a target for the development of anticancer drugs Microtubule-damaging agents suppress microtubule dynamics, leading to disruption of the mitotic spindle in dividing cells, cell cycle arrest at M phase, and late apoptosis A better understanding of the processes coupling microtubule damage to the onset of apoptosis will reveal sites of potential intervention in cancer chemotherapy Inhibition of microtubule dynamics induces persistent modification of biological processes (M arrest) and signaling pathways (mitotic spindle assembly checkpoint activation, Bcl-2 phosphorylation, c-Jun NH2-terminal kinase activation), which ultimately lead to apoptosis through the accumulation of signals that finally reach the threshold for the onset of apoptosis or through diminishing the threshold for engagement of cell death Microtubules serve also as scaffolds for signaling molecules that regulate apoptosis, such as Bim and survivin, and their release from microtubules affect the activities of these apoptosis regulators Thus, sustained modification of signaling routes and changes in the scaffolding properties of microtubules seem to constitute two major processes in the apoptotic response induced by microtubule-interfering agents

Microtubules, microtubule-interfering agents and apoptosis

Epothilone A and B—Novel 16-Membered Macrolides with Cytotoxic Activity: Isolation, Crystal Structure, and Conformation in Solution†

In addition to epothilones A (1) and B (2), 37 natural epothilone variants and epothilone-related compounds were isolated from the culture broth of a 700 L fermentation of Sorangium cellulosum, strain So ce90/B2. Of these, only the 12,13-desoxyepothilones, epothilone C (14) and D (15), were produced in significant amounts (3-6 mg/L); the 21-hydroxy derivatives and epothilones E (3) and F (4), in low and variable amounts due to further degradation by the producing organism. Most of the other epothilone variants were produced only in 1-100 microg/L amounts. The new compounds are very similar in structure to the parent compounds 1, 2 and 14, 15 and are presumably the result of the imperfect selectivity of the biosynthetic enzymes for acetate and propionate. Further, epothilones containing an oxazole moiety (10-13) in the side chain instead of a thiazole as well as ring-expanded 18-membered macrolides, epothilones I (30-35), and a ring contracted 14-membered macrolide, epothilone K (36), were found as very minor metabolites. The mutant strain, So ce90/D13, instead of macrolactones, produced short-chain carboxylic acids 40, 41, and 42 bearing the characteristic thiazole side chain. The structures of the new epothilones were elucidated on the basis of comprehensive NMR and MS data. The new epothilone variants were tested in a cytotoxicity assay with mouse fibroblasts (cell line L929), and structure-activity relationships were established. Several new natural epothilones showed activity comparable to 1 and 2, but in no case exceeded that of 2.

New natural epothilones from Sorangium cellulosum, strains So ce90/B2 and So ce90/D13: isolation, structure elucidation, and SAR studies.

The present invention concerns the epothilone, especially epothilone C (R = hydrogen) and epothilone D (R = methyl) of formula (I), as well as epothilone E (R = hydrogen) and epothilone F (R = methyl) of formula (II), the production process and their application for producing therapeutic agents, including cytostatic agents, as well as phytosanitary agents.

Epothilone c, d, e and f, production process, and their use as cytostatic as well as phytosanitary agents

The structure-activity relationships of epothilones indicate that major modifica- tions are only tolerated in the western ring segment. In particular, C2 methyl of the thiazole ring appears to be most flexible. Its broad modification started from epothilone F, which was obtained from natural epothilone B by hydroxylation via the N-oxide. Some of the prepared derivatives exhibit improved esterase stability in addition to high cytotoxic activity. For these and other favorable properties, amine (BMS-310705) was recently introduced in clinical trials. In an alternative approach, modified side chains were introduced by replacement of the C12,C15 ring segment via ring-opening olefin metathesis (ROM) of epothilone C in the pres- ence of ethylene to 12,13-seco-epothilone C, introduction of a synthetic building block fol- lowed by ring-closing olefin metathesis (RCM), and epoxidation to the 16-alkyne analog of epothilone A. The structure of the tetrapeptide tubulysin D was confirmed by total hydrolysis to N-methyl D-pipecolic acid, L-isoleucine, tubuvaline (Tuv), tubuphenylalanine (Tup), formaldehyde, and 3-methylbutyric acid. Mild acidic hydrolysis to cyclo-tubulysin and oxidative degradation to L-valine allowed the assignment of the stereocenters of Tuv, hydrazi- nolysis, and comparison with synthetic reference samples to that of Tup. The absolute con- figuration of tubulysin D is: (R)-Mep, (2S,3S)-Ile, (1'R,3'R)-Tuv, and (2S,4R)-Tup.

/pdf/semisynthesis-and-degradation-of-the-tubulin-inhibitors-43nafzz8vg.pdf

Semisynthesis and degradation of the tubulin inhibitors epothilone and tubulysin

The invention relates to a compound of the following general formula (tubulysin) with the following definitions for R, R1, R2, R3, R4, R5, R6, R7, R8 R9, R10, R11, S, T, U, V, W, X, Y and Z: R = H, C1-4 alkyl, aryl, OR1, NR1R2 or NH-(CH2)2-4-; R1 = H, C1-6 alkyl or aryl; R2 = H, C1-6 alkyl or aryl; S = H, Hal, NO2 or NHR3; U = H, Hal, NO2 or NHR3; R3 = H, HCO or C1-4 alkyl-CO; T = H or OR4; R4 = H, C1-4 alkyl, aryl, COR5, P (O) (OR6)2 or SO3R6; R5 = C1-6 alkyl, alkenyl, aryl or heteroaryl; R6 = H, C1-4 alkyl or metal ion; V = H or R7 or (if W = O) O; R7 = H, C1-4 alkyl or COR8; R8 = C-1-4 alkyl, alkenyl or aryl; W = H or C1-4 alkyl or (if V = O) O; X = H, C1-4 alkyl, alkenyl or CH20R9; R9 = H, C1-4 alkyl, alkenyl, aryl or COR10; R10 = C1-6 alkyl, alkenyl, aryl or heteroaryl; Y = (if Z = CH3 or COR11) a free electron pair or (if Z = CH3) O; R11 = C1-4 alkyl, CF3 or aryl and/or Z = (if Y = O or a free electron pair) CH3 or (if Y = free electron pair) COR11.

Heinrich Steinmetz

Papers

Epothilone A and B—Novel 16-Membered Macrolides with Cytotoxic Activity: Isolation, Crystal Structure, and Conformation in Solution†

New natural epothilones from Sorangium cellulosum, strains So ce90/B2 and So ce90/D13: isolation, structure elucidation, and SAR studies.

Epothilone c, d, e and f, production process, and their use as cytostatic as well as phytosanitary agents

Semisynthesis and degradation of the tubulin inhibitors epothilone and tubulysin

Tubulysins, method for producing the same and tubulysin preparations