Biomimetic building

O. Koelman, Biomimetic Buildings Understanding Applying the Lessons of Nature, Rocky Mountain Institute Solutions, Snowmass, CO, 2003. 

Tandem reaction strategies can accomplish several synthetic objectives in a single step.6 The rapidity with which they can build up molecular complexity is a most useful and impressive virtue. For example, cation-induced, biomimetic polyolefinic cyclizations7 are among the most productive and atom-economical8 single-step transformations known in organic chemistry. In one of the most spectac-... 

The enzymatic conversion of a-(aminomethyl)pyrroles is also used by nature to produce porphyrinogens like uroporphyrinogen III (see introduction, compound 8), which is the key building block in the biosynthesis of all known porphinoid natural products. This biomimetic method is a powerful tool for the synthesis of different porphyrins, e.g. for the preparation of JV,Af, V ,Ar"-tetramethylporphyrin-2,3,7,8,12,13,17,18-octaacetic acid dibromide 12.36... 

The biomimetic approach can be easily extended to the synthesis of [26]porphyrins(3.3.3.3) 32 when symmetrically -substituted 2-(3-hydroxypropen-l-yl)pyrroles 30 are used as mono-pyrrolic building blocks.1 la h... 

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

Moody and coworkers have employed a biomimetic hetero-Diels-Alder-aroma-tization sequence for the construction of the 2,3-dithiazolepyridine core unit in amythiamicin D and related thiopeptide antibiotics (Scheme 6.243 a) [426]. The key cycloaddition reaction between the azadiene and enamine components was carried out by microwave irradiation at 120 °C for 12 h and gave the required 2,3,6-tris(thi-azolyl)pyridine intermediate in a moderate 33% yield. Coupling of the remaining building blocks then completed the first total synthesis of the thiopeptide antibiotic... 

In natural processes, metal ions are often in high oxidation states (2 or 3), whereas in chemical systems the metals are in low oxidation states (0 or 1). This fact inverts the role of the metal center, such that it acts as a one-electron sink in a natural system, but as a nucleophile in an artificial ones (see other chapters of this book and the review by Aresta et al. [109]). Nevertheless, important biochemical processes such as the reversible enzymatic hydration of C02, or the formation of metal carbamates, may serve as natural models for many synthetic purposes. Starting from the properties of carbonic anhydrase (a zinc metalloenzyme that performs the activation of C02), Schenk et al. proposed a review [110] of perspectives to build biomimetic chemical catalysts by means of high-level DFT or ah initio calculations for both the gas phase and in the condensed state. The fixation of C02 by Zn(II) complexes to undergo the hydration of C02 (Figure 4.17) the use of Cr, Co, or Zn complexes as catalysts for the coordination-insertion reaction of C02 with epoxides and the theoretical aspects of carbamate synthesis, especially for the formation of Mg2+ and Li+ carbamates, are discussed in the review of Schenk... 

A problem with the formation of the ternary ES—02 adduct is that it entails an attack of triplet 02 on the singlet substrate, which is a forbidden reaction. However, the presence of iron(III) may provide a mechanism for relaxing this barrier, as suggested by biomimetic studies showing that oxidative cleavage of catechols can be catalyzed by iron(III) centers [145,146], Building on this important early work, Que and coworkers synthesized a series of [Fe(L)(dbc)] complexes where L is a tetradentate tripodal ligand based on trimethylamine with... 

Abstract Calix[n]arenes represent a well-known family of macrocyclic molecules with a broad range of potential applications in many branches of supramolecular chemistry. Because of their preorganisation, calix[n] arenes are frequently used as building blocks and molecular scaffolds in the construction of more elaborate systems, such as artificial enzyme biomimetics and receptors. This review is focused on the recent development of calixarene-based anion receptors. 

It will be of some interest to learn how to build catalysts to handle the particular substrates that natural enzymes cleave, at a rate comparable to the rates of those enzymatic reactions. However, one of the aims of biomimetic chemistry is to extend the kinds of rates and selec-tivities of enzymatic reactions into reactions for which natural enzymes have not been optimized and to substrates that are neither recognized nor handled by normal enzymes. It is clear that we already have achieved this, even though our ribonuclease model system has some distance to go before it can approach the kinds of rates we have observed in the cyclodextrin ferrocinnamate ester reaction, for instance. In lock and key chemistry, the keys that fit artificial enzymes best are not the same as the keys that open the natural enzyme locks. 

Finally, the best building blocks identified can be coupled in a modular way to complete photocatalytic reaction cycles, which then should be able to mimic a certain biological process. If these bioinspired photocatalytic systems are performing rmder identical conditions as their native counterparts, a direct comparison of quantitative criteria such as turnover frequencies and the total number of catal5dic cycles is possible and should always be the finad goal to demonstrate the potential usefulness of the biomimetic process. 

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