Biomimetic approaches

The real breakthrough toward synthesis of vinblastine and, in fact, the first significant laboratory preparation of binary indole-indoline alkaloids with the natural C-16 -C14 PARF configuration, was due to the work of the Potier-Langlois team at Gif (38,39 for reviews, see Refs. 40 and 41), buttressed by results obtained by the Kutney group in Vancouver (42,43,44), and the efforts of Atta-ur-Rahman and associates in Karachi. Their basic idea, which relied on the biogenetic consideration that binary indole-indoline alkaloids are formed in plants by the union of vindoline 

For a synthesis of leurosidine (56), 15,20-dihydrocatharanthine iV-oxide (57) was subjected to coupling with vindoline (3) under the modified Polo-novski conditions. The initial adduct, imonium salt 58, was converted to the enamine 59 in base. Oxidation of this product with osmium tetrox-ide proceeded chemo- and stereoselectively, without reaction of the 

Anhydrovinblastine (42) was produced from 15-(3-acetoxy-20-a-ethyldi-hydrocatharanthine (65) in that study [63,64-, an identical observation has been reported by Langlois et al. (65,66)], while the Kutney group reported the formation of 15-a-acetoxy-20-deoxyleurosidine (66) for this reaction 67,68). In all cases the major products of the reactions, 67-69, were again 

Application of the modified Polonovski reaction to catharanthine p-ep-oxide (73) afforded leurosine (74) in 6% (75) or 20% yield (70-74), thus 

Atta-ur-Rahman et al. reported the oxidation of catharanthine by a modified Prevost reaction to result in formation of the 20-a-acetoxy derivative. Coupling of its A-oxide (77) to vindoline, using trichloroacetic anhydride (rather than the usual trifluoro compound), and subsequent re- 

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The biomimetic approach to total synthesis draws inspiration from the enzyme-catalyzed conversion of squalene oxide (2) to lanosterol (3) (through polyolefinic cyclization and subsequent rearrangement), a biosynthetic precursor of cholesterol, and the related conversion of squalene oxide (2) to the plant triterpenoid dammaradienol (4) (see Scheme la).3 The dramatic productivity of these enzyme-mediated transformations is obvious in one impressive step, squalene oxide (2), a molecule harboring only a single asymmetric carbon atom, is converted into a stereochemically complex polycyclic framework in a manner that is stereospecific. In both cases, four carbocyclic rings are created at the expense of a single oxirane ring. 

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... 

These results have demonstrated that the biomimetic approach of copying the supramolecular principle of archaeal cell envelopes opens new possibilities for exploiting functional hpid membranes at meso- and macroscopic scales. Moreover, this technology has the potential to initiate a broad spectrum of developments in such areas as sensor technology, diagnostics, biotechnology, and electronic or optical devices. 

Another important area of future development concerns copying the supramolecular principle of cell envelopes of archaea, which have evolved in the most extreme and hostile ecosystems. This biomimetic approach is expected to lead to new technologies for stabilizing fnnctional lipid membranes and their nse at the mesoscopic and macroscopic scales [200]. Along the same line, liposomes coated with S-layer lattices resemble archaeal cell envelopes or virns envelopes. Since liposomes have a broad application potential, particu-... 

Two examples stand out research on ceramic precursors and research on biomaterials via so-called biomimetic approaches. I had started the systematic organometallic precursor work for making ceramic powders in a series of a few dozen papers starting in 1948 (1, 2). By the mid-1950s I had shown that inorganic sols did essentially as well and were orders of magnitude cheaper. The very sophisticated ceramic precursor work, now a decade old, has yet to demonstrate a special niche for itself in any real examples with unique properties. 

Knowledge regarding biosyntheses has induced several biomimetic approaches towards steroids, the first examples being described by van Tamelen [10] and Corey [11]. A more efficient process was developed by Johnson [12] who, to synthesize progesterone 0-10 used an acid-catalyzed polycyclization of the tertiary allylic alcohol 0-7 in the presence of ethylene carbonate, which led to 0-9 via 0-8 (Scheme 0.3). The cyclopentene moiety in 0-9 is then transformed into the cyclohexanone moiety in progesterone (0-10). 

The biomimetic approach to the core skeleton of C-nor-D-homosteroid was first developed by the Merck research group (Scheme 2.1) [16]. In the Merck procedure,... 

The isolation of calycanthine (9) in 1888 by Eccles [28] and the subsequent proposition for its origins in the oxidative dimerization of tryptamine by Woodward [29] and Robinson [30] had prompted several key synthetic studies based on a biomimetic approach. Hendrickson was the first to experimentally verify the plausibility of forming the C3-C3 linked dimers through an oxidative radical dimerization strategy (Scheme 9.2a). He demonstrated that the sodium enolate of a tryptamine-derived oxindole could be oxidized with iodine to afford a mixture of three possible stereoisomers. The racemic product was isolated in 13 % yield, while the meso product was isolated in 8 % yield. Global reduction of the oxindole and carbamates afforded the first synthetic samples of chimonanthine (7) [9a],... 

As indicated above, the development of bio-nanohybrids by mimicking biomineralization represents an extraordinarily useful approach. This is, for instance, the case for those bio-nanocomposites based on bone biomimetic approaches, which show excellent structural properties and biocompatibility. They are prepared by... 

Coradin, T., Durupthy, O. and Livage, J. (2002) Interactions of amino-containing peptides with sodium silicate and colloidal silica A biomimetic approach to silicification. Langmuir, 18, 2331-2336. 

In this chapter, we will introduce a bioinspired approach to biomineralization. First, a fundamental concept of the bioinspired approach is compared with the biomimetic approach. Here is a question, What is a bioinspired approach If we want to fly in the sky, when we look at flying birds what do we have to do Two kinds of typical answer were considered, as shown in Figure 6.4. One is Bird-Man, in the Edo period (AD 1600) in Japan, a man named Kokichi attempted to fly. He wore wide, large wings on both his arms, and fluttered his arms vigorously, but in vain. This is a typical biomimetic approach. He only mimicked the style of a flying bird, so his innovative idea ended in failure. 

Fig. 6.4 Schematic illustration of a fundamental concept of a bioinspired approach relative to a biomimetic approach.

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