Antibodies 38C2 antibody

Like many other antibodies, the activity of antibody 14D9 is sufficient for preparative application, yet it remains modest when compared to that of enzymes. The protein is relatively difficult to produce, although a recombinant format as a fusion vdth the NusA protein was found to provide the antibody in soluble form with good activity [20]. It should be mentioned that aldolase catalytic antibodies operating by an enamine mechanism, obtained by the principle of reactive immunization mentioned above [15], represent another example of enantioselective antibodies, which have proven to be preparatively useful in organic synthesis [21]. One such aldolase antibody, antibody 38C2, is commercially available and provides a useful alternative to natural aldolases to prepare a variety of enantiomerically pure aldol products, which are otherwise difficult to prepare, allovdng applications in natural product synthesis [22]. 

Shamis, M. Lode, H. N. Shabat, D. Bioactivation of self-immolative dendritic prodrugs by catalytic antibody 38C2. J. Am. Chem. Soc. 2004, 126, 1726-1731. 

Figure 19 A success of the reactive immunization strategy. Aldolization reaction catalyzed by antibody 38C2 raised against a /3-, 3-diketone hapten.

On the basis of encouraging work in the development of L-proline-DMSO and L-proline-ionic liquid systems for practical asymmetric aldol reactions, an aldolase antibody 38C2 was evaluated in the ionic liquid [BMIM]PF6 as a reusable aldolase-ionic liquid catalytic system for the aldol synthesis of oc-chloro- 3-hydroxy compounds (288). The biocatalytic process was followed by chemical catalysis using Et3N in the ionic liquid [BMIM]TfO at room temperature, which transformed the oc-chloro-(3-hydroxy compounds to the optically active (70% ee) oc, (3-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was also shown to be reusable for Michael additions and the reaction of fluoromethylated imines. 

Notes Chiral preparations include the proline-catalyzed reactions2 and recently an aldolase antibody 38C2 method has been reported.3 See also 4... 

An intramolecular asymmetric Michael addition of aldehydes and ketones - to give cyclopentanals - gives the otherwise disfavoured d.v-producls when catalysed with (f) antibody 38C2, the first commercially available catalytic antibody 222 One case gave 99% de, 98% ee. ... 

A novel antibody-catalysed intramolecular Michael addition of aldehydes and ketones to enones [(148) -> (149)] has been accomplished. The reaction is enantio- and diastereo-selective with a high ee and cis/trans ratio. Antibody 38C2 is the only catalyst to date capable of generating this selectivity in Michael addition products.177... 

Diketone 4 was used for immunization, and two out of twenty monoclonal antibodies produced showed the characteristic enaminone absorb-tion at 315 nm after incubation with the diketone. Only these two antibodies, 38C2 and 33F12, were aldol catalysts (Wagner et al 1995). For example, 38C2 catalyzes the aldol reaction between acetone and aldehyde 5 to give aldol 6 with cat = 6.7 X 10 3 min-1 and = 17 (Scheme 4). 

It soon became clear that aldolase antibody 38C2 catalyzed the aldol reaction with both efficiency and broad scope. For example, compounds 7 to 13 could all be synthesized in antibody 38C2 catalyzed aldol reactions (Hoffmann et al, 1998). 

Because an equilibrium constant is not affected by catalysis, an enzyme that accelerates a forward reaction must also accelerate the reverse or retro-reaction. Furthermore, the enantioselectivity for both reactions will be identical. Antibody 38C2 catalyzes both the forward and retro-aldol reaction, and we envisioned that it may be useful in the kinetic resolution of aldols. Because the product enantiomer from the forward aldol reaction is the substrate in the retro-aldol reaction, the opposite... 

Indeed, we have found antibody 38C2 to be an efficient catalyst for the retro-aldol reaction of tertiary aldols. Aldols (R) —19 through (S)— 26 were synthesized via kinetic resolution with 38C2 (List et al., 1999). The resolution of aldols (S) — 24, (R)— 25, and (5)—26 demonstrates the potential of aldehyde aldols. Aldehyde aldols provide facile access to acetate aldols that are otherwise difficult to obtain by more traditional techniques (Saito et al., 1999). 

Fig. 6. Growth inhibition of HT29 human colona carcinoma cells by procamptothecin in the presence of increasing concentrations of antibody 38C2. Filled triangle untreated control open square 1 /j t procamptothecin filled square 1 /rM camptothecin. Bars indicate SD, n = 4.

Scheme 4.6 1,3-Diketone 15, used as a hapten to raise antibody 38C2, traps the reactive, active-site amine of LysH93 to form a stable, chromophoric vinylogous amide.

In theory, the programmable stereoselectivities of catalytic antibodies makes them well suited for asymmetric synthesis. Several such transformations have been carried out on a preparative scale. Kinetic resolution of the epothilone precursor 19 with the aldolase antibody 38C2 is instructive (Scheme 4.9) [57]. The reaction proceeds in good yield (37 %) and high enantiomeric excess (90 %). However, so much catalyst is needed (0.5 g of IgG antibody was used for the resolution of 0.75 g 19) that large-scale production is likely to be impractical in many cases. As most antibody catalysts are much less efficient than the aldolases, catalyst costs will generally be appreciable. 

Scheme 4.11 Activation of a prodrug of the anticancer agent eto-poside via tandem retro-aldol/retro-Michael reactions catalyzed by antibody 38C2.

The development of the concept of reactive immunization yielded more effective antibody aldolases.119-120 In this new approach, rather than raise antibodies against an unreactive hapten designed to mimic the transition state, the antibodies were raised against a reactive moiety. Specifically, a p-diketone that serves as a chemical trap to imprint a lysine residue in the active site of the Ab (Scheme 5.65) was used.340 A reactive lysine is a requirement of the type I aldolase mechanism. By this method two aldolase catalytic antibodies, 38C2 and 33F12 were identified.119... 

Since the preparation of enantiomerically pure tertiary aldols remains a challenge, aldolase antibody 38C2 was investigated as a catalyst for the kinetic resolution of racemic tertiary aldols. Ab38C2 was demonstrated to be an efficient catalyst for the retro-aldol reaction of the fluorogenic tertiary aldol /m-methodol (Scheme 5.68) and exhibited an E value of >159 50. At 50% conversion, (R)-terMnethodol is obtained with an enantiomeric excess of >99% ee. Consequently the ability of Ab38C2 to resolve tertiary alcohol was exploited in the enantioselective synthesis of ( )-frontalin (Scheme 5.69).125... 

ALDOLASE ANTIBODY 38C2 PROMOTED ALDOL REACTION... 

Although the use of enzymes in ionic liquids has been explored, the enzymatic carbon-carbon bond forming the reactions in ionic liquids has not been studied in detail. Since aldol reactions catalyzed by the aldolase antibody 38C2 in buffer... 

A proposed mechanism for the Michael addition reaction is shown in Scheme 10.7. Note that enamine, generated from the reaction of hydroxyacetone and aldolase antibody 38C2, reacts with the activated methylene group in 2-(phenyl)ethyl-2-(tri-fluoromethyl)acrylate. 

List B, Lemer RA, Barbas CF 111. Enantioselective aldol cyclodehydrations catalyzed by antibody 38C2. Oig. Lett. 1999 1(1) 59-61. 

Aldolase antibodies 38C2 and 33F12 are able to catalyze both the aldol addition and the retro-aldol reaction [99]. These catalysts have been employed to carry out the kinetic resolution of /3-hydroxyketones [100] and have been found to catalyze the asymmetric aldol reactions of 23 donors (ketones) and 16 acceptors (aldehydes) [101]. A highly efficient enantioselective... 

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