Biomimetic reaction

Naturally occurring monoterpene alcohols were heated in water without prior deri-vatization with typical biological water-solubilizing groups, for example phosphates or glycosidic units. Biomimetic reactions that normally would be acid-catalyzed, proceeded on the underivatized compounds in the absence of added acidulant. Cooling of the mixtures rendered the products insoluble and readily isolable, and the aqueous phase did not require neutralization before work-up. 

Nerol and linalool underwent considerably more elimination than did geraniol, to give the same hydrocarbons. The major products and their relative proportions were consistent with those for carbocationic rearrangement of derivatives of linalool, nerol, and geraniol under acidic conditions. 

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Biomimetic reactions catalyzed by cydodextrins and their derivatives 98CRV1997. 

Finally, 18 has been obtained directly from 3(R)-vobasinediol (58) in a facile way (Scheme 20). It seems that all the expected reactions mentioned above have been completed in one pot within 2.5 hr and under relatively mild conditions. The substitution of 58 with 73 as the starting material gives similar results. In this case, the yield of 18 is 25%. In this one-pot reaction, control of the reaction conditions seems to be very delicate, and the presence of sulfuric acid as well as mild treatment with H202 followed by immediate removal of the excess of oxidizing agent prove to be quite crucial. The mechanism of this biomimetic reaction has been proposed (Scheme 21). 

Biomimetic reactions should also be considered for the preparation of optically active cyanohydrins (using a cyclic dipeptide as catalyst) and also for the epoxidation of a, (3-unsaturated ketones (using polyleucine or congener as a catalyst). 

See for example the pioneering work of Breslow Bres-low, R. Dong, S. D. Biomimetic Reactions Catalyzed by Cyclodextrins and their Derivatives Chem. Rev. 1998, 98,1997-2011 and Breslow, R. Biomimetic Chemistiy and Artificial Enzymes - Catalysis by Design Acc Chem. Res. 1995,28,146-153. 

Another interesting example is the synthesis of 77-(2-thiazolyl)-nortropinon 121. Stoll and co-authors [175] described the synthesis of this drug-like product via the legendary first total synthetic approach proposed by Robinson in 1917 [176] for the natural alkoloid tropinone, also well known as a good example of biomimetic reaction. In this tandem treatment, 2-aminothiazole was reacted with succinaldehyde and acetonedicarboxylic acid yielding 77-(2-thiazolyl)-nortropinon 121 in moderate yields (Scheme 58). 

Shizuri, Y., Yamaguchi, S., Terada, Y. and Yamamura, S. (1987a). Biomimetic reaction of germacrene-D epoxides in connection with periplanone A. Tetrahedron Letters 28 1791-1794. 

Although the preceding catalase biomimetic reactions are important, the true biological role of the OEC is to evolve 02 from H20. Only a few complexes evolve 02 from H20 and even fewer contain Mn (see complex 67). Perhaps the best known case is the catalytic oxidation of water by the dinuclear ruthenium complex [(bpy)2(H20)Ru0Ru(H20)(bpy)2]4+ 68, which has been well documented [9,160] and will not be discussed here. 

Breslow, R., Dong, S. D., (1998) Biomimetic reactions catalyzed by cyclodextrins and their derivatives Chem. Rev. 98, 1997-2011. 

In the simulation of enzymes attempts have been made to use steroid matrices and biomimetic reactions of polyene cyclization, comprehensively described in Ref. [10]. 

We will learn to produce mimics of enzyme clusters, imitating natural clusters such as gene transcription assemblies. We will learn to produce artificial enzymes that show induced fit, and allosteric control by analogs of hormones. Then we will move to mimics of cells themselves, with their components of many enzymes, to achieve chemical processes more complex than those done by a single enzyme. The biochemistry of life is impressive, but the role of chemistry is not just to admire it. As humans were impelled to invent ways to fly after observing birds, we will learn to create a new area of chemistry - biomimetic reaction chemistry - adding both to our understanding and to our practical abilities. 

Other biomimetic reactions are based on the catalytic properties of metal ions. Many enzymes require metal ions that function, in one way or another, in oxidation-reduction processes. The wide range of such metal-ion reactions precludes mentioning more than a few in addition to the iron-porphyrin class, and in addition to chlorophyll, a number of enzymes require cobalamin as cofactor ferridoxin and high-potential iron proteins require iron-sulfur clusters, and nitrog-... 

The effects of metal ions in promoting hydrolytic reactions have been noted by many investigators (56, 57). Probably the most spectacular of these biomimetic reactions come from the work of Sargeson, Buckingham, and their collaborators (58, 59). They have made a number of cobalt complexes of various esters, and found that the rates of... 

No list of biomimetic reactions could possibly be complete, and the list above obviously covers only a few of many examples that could be chosen for discussion. They do introduce, however, several important examples. 

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