Discodermolide isolation

The discodermolide isolated from the 6 g campaign proved to be a monohydrate. In agreement with our quality assurance department, we could only use the material from the 60 g campaign and eventually the 500 g campaign without repeating the toxicology if the following conditions were met a) the synthetic route was identical, b) the material produced had the same side product profile c) the material was equally pure or better and d) the same crystal modification was produced (8 or 9 modifications are known) and e) the material was sterile. 

Scheme 2.6 shows some examples of the use of chiral auxiliaries in the aldol and Mukaiyama reactions. The reaction in Entry 1 involves an achiral aldehyde and the chiral auxiliary is the only influence on the reaction diastereoselectivity, which is very high. The Z-boron enolate results in syn diastereoselectivity. Entry 2 has both an a-methyl and a (3-benzyloxy substituent in the aldehyde reactant. The 2,3-syn relationship arises from the Z-configuration of the enolate, and the 3,4-anti stereochemistry is determined by the stereocenters in the aldehyde. The product was isolated as an ester after methanolysis. Entry 3, which is very similar to Entry 2, was done on a 60-kg scale in a process development investigation for the potential antitumor agent (+)-discodermolide (see page 1244). 

The natural product eleutherobin (1) was isolated in 1994 by Fenical et al. from a marine soft coral from an Eleutherobia species and its structure was elucidated shortly afterwards (Figure 1) [1]. Eleutherobin is a diterpene glycoside that possesses remarkable cytotoxicity against a wide variety of cancer cells, which is likely to be based on binding to tubulin and stabilization of microtubules [2, 3]. Mitosis is interrupted and the cell division cycle is terminated. The mechanism of action of eleutherobin is comparable to that of highly potent cytostatic agents such as paclitaxel (Taxol), nonataxel, epothilones, and discodermolide. 

Locate all the tetrahedral stereogenic centers in discodermolide, a natural product isolated from the Caribbean marine sponge Discodermia dissoluta. Discodermolide is a potent tumor inhibitor, and shows promise as a drug for treating colon, ovarian, and breast cancers. 

Discodermolide (22) is a polypropionate-based, unique compound isolated from the Caribbean deep-sea sponge Disco-dermia dissoluta. It is immunosuppressive as well as highly cytotoxic. More significantly, it stabilizes microtubules more potently than taxol (2). 

Discodermolide (88) was isolated from Discodermia disso-luta by using a P388 cell line toxicity bioassay later it was... 

Investigation of the microbial population associated with Discodermia using 16s-rRNA analysis showed the presence of significant microbial diversity. Although the case for microbial production is still speculative, we have begun a project aimed at the development of novel isolation and culture media in order to try to harness this potential supply of discodermolide. To date, over 800 microbial isolates have been isolated from Discodermia... 

ABSTRACT Discodermolide and pironetin are two immunosuppressive agents with antitumor activity. The isolation, structure elucidation, biological activity are reported as well as the synthetic routes to these two compounds. Five syntheses of discodermolide and seven syntheses of pironetin are described. 

Discodermolide is a unique polyketide isolated in 1990 by Gunasekera et al. at the Harbor Branch Oceanographic Institute from the Caribbean deep sea sponge Discodermia dissoluta [1-2]. Methanol/toluene (3 1) solvent extraction of the sponge yielded an extract that was partitioned between ethyl acetate and water. By silica gel and reverse-phase chromatography, (+)-discodermolide was purified from the ethyl acetate-soluble material and obtained as crystalline solid in 0.002% yield (w/w from frozen sponge). 

The compound supply for development cannot be met through the isolation and purification of discodermolide from Discodermia sp. (which must be harvested using manned submersibles). Attempts to reproducibly isolate a discodermolide-producing microorganism for fermentation have not been successful to date. Therefore, all discodermolide used for late preclinical research and development activities as well as for the ongoing... 

The following anecdote illustrates the pitfalls into which one can stumble. During the scale-up of this process for the third (500 g) discodermolide campaign, the first reaction did not deliver the required yield of 30%. Only some 18% of 4 was isolated along with starting material. This result created some consternation until we realized that the sodium hexamethyldisilazide, used as a base in this sequence, is supplied as a 35% solution in THF. As we carried out the reaction in winter it was quite cold and somehow the THF solution of sodium... 

We settled on running 3 batches under carefully optimized HCl/MeOH conditions after a brief examination of the alternatives. The first reaction we attempted with 65 during the 60 g campaign produced a 40% yield of 1 after chromatography The reason was simple although not obvious. The first reaction to occur is cyclization to the fully silylated discodermolide 68. This compound oils out of the reaction mixture and distributes itself around the walls of the reactor. During the reaction monitoring this is not obvious and only becomes so after work-up. The trisilylated discodermolide 68 can be isolated and separately hydrolyzed (see below). 

The solution was simple Adjusting the pH to 4 kept the lactone ring closed (HPLC on bottom of Figure 16). Thus the material from the three columns was redissolved in acetonitrile/water 9/1 and the pH adjusted to 4 with HCl. After partial evaporation and crystallization (+)-discodermolide was isolated in 95% yield as the monohydrate with the desired crystal modification formed. The purity was 99.9% with loss on drying of 3.1%. The optical rotation was (+) 19° (0.5% in acetonitrile). It contained around 600 ppm of acetonitrile as residual solvent. This could not be removed by drying. 

The combination of NMR spectroscopy and X-ray crystallographic analysis revealed a novel polypropionate structure for discodermolide (104) [114], a polyhydroxylated lactone isolated from Discodermia... 

Discodermolide (36) is a cytotoxic polyketide isolated in low yield from the Caribbean sponge Discodermia dissoluta 44), The recent discovery that discodermolide shares the same microtubule-stabilising mechanism of antimitotic action as the clinically important anticancer drug, Taxol (paclitaxel), and retains activity against Taxol -resistant cancer cells has stimulated considerable interest (45,46). Due to the scarce supply of the natural material, the development of an efficient total synthesis (47-52) of (+)-discodermolide is needed to provide useful quantities for further testing, as well as enabling access to structurally simplified analogues. 

In the effort of total synthesis of discodemolide, the Still-Gennari type HWE reaction was also used by Paterson and Lyothier to form the Cg-C9 olefin. Phosphonate 94 was treated with NaH in THE at 0 °C for 30 min prior to the addition of aldehyde 93. The crude product showed a mixture of (Z)- and ( )-olefins, 95 and 96, in a 5 1 ratio. The desired (Z)-isomer 96 could be isolated by flash chromatography in 73% yield. The (Z)-enone 96 was further treated with K-Selectride at 25 C for 24 h. A single diastereomeric alcohol 97 was formed selectively and isolated in 59% yield. This alcohol processing (7/ )-configuration was leading to 1-epi-discodermolide 98 as final product by four additional reactions. 

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