Syntheses of optically pure

On the other hand, adults of E. varivestis turned out to be the most versatile alkaloid producer of all ladybird species so far examined. Indeed, not less than 12 alkaloids have been isolated from this beetle, including euphococcinine (32), a complex mixture of simple piperidines (33-36), 2-phenylethylamine (37) and long chain pyrrolidines (38-41) (Fig. 7) [43-45]. The syntheses of optically pure (2S,12 R)-2-(12 -aminotridecyl)-pyrrolidine (38) and (2S,12 R)-l-(2"-hydroxy-... 

Similarly, syntheses of optically pure pyrrolobenzodiazepines (70) were effected with PIFA using the proline-derived hydroxamic esters (69) (equation 8) . ... 

The synthesis of camphor (80% optical purity) by heating optically pure di-hydrocarvone at 400 °C for 20 h is reminiscent of Money s racemic camphor synthesis (Vol. 1, p. 39) in that both correspond to a biogenetic-type synthesis via enol formation. Further synthetic work on deuteriated camphors (see references therein and Vol. 3, p. 67 Vol. 4, p. 48 Vol. 7, p. 38 for earlier work) includes syntheses of optically pure [8- Hi]-, [8- H2]-, and [8- H3]-(—)-camphor (204) by modification of known reactions (Scheme 5) and the use of an improved Zn-Cu... 

Similarly, regio- and stereoselective syntheses of optically pure fused or bridged 1,2,5-oxadiazepines have been reported via intramolecular nitrone-alkene cycloaddition <2005EJ01680>. 

The Ferrier-I rearrangement represents now a classical methodology which should be considered in planning the syntheses of optically pure targets from sugar chirons. Such a conclusion may be illustrated by the preparation of p)ranosyl nucleosides obtained by this procedure. 

The 2,3-dihydro-1,4-benzodioxin ring system has aroused increasing interest, owing to its presence in a large number of structures of important therapeutic agents, the activity of which is considerably influenced by the chirality of the heterocyclic unit. Most of the syntheses of optically pure 2-substituted-2,3-dihydro-1,4-benzodioxins start from 2-hydroxymethyl-2,3-dihydro-1,4-benzodioxin in chiral form this latter compound can be obtained from D-mannitol <76CC92l>, by direct con-... 

Blockers Lipases Several alternative schemes have been described for the syntheses of optically pure intermediates of (3-blockers [75-77]... 

K. M. Smith, G. M. F. Bisset and M. J. Bushell, Partial syntheses of optically pure methyl bacteriopheophorbides-c and -d ftom methyl-phaeophorbide-a, y. Org. Chem. 45,2218 (1980). 

This chapter will be divided into two distinct parts. Firstly, general methods for making Ti -arene chromium tricarbonyl complexes will be discussed. Particular attention will be paid to complexes bearing sulfinyl substituents and protocols for their synthesis will be given. The second part will deal with enantiopure or enriched complexes. Examples of diastereoselective syntheses of optically pure 1,2-disubstituted complexes with amino and hydroxyl groups at the two benzylic positions will be presented. 

Botha, J. J., D. A. Young, D. Ferreira, and D. G. Roux Synthesis of condensed tannins. Part 1. Stereoselective and stereospecific syntheses of optically pure 4-arylflavan-3-ols, and assessment of their absolute stereochemistry at C-4 by means of circular dichroism. J. Chem. Soc. Perkin I 1981, 1213. 

These amino acids were initially synthesized by asymmetric aminomethylation of optically pure (R)- and (S)-N-Acyl-4-phenyhnethyl)oxazolidin-2-ones 52 through TiCVenolates (Evans methodology [135]) with (benzoylamino)methylchloride or benzyl N-(methoxymethyl)carbamate [66, 97-99, 104]. Hydrolytic removal of the auxiliary yielded the N-protected (benzoyl or Z) amino acid 54. Deprotection afforded the free amino acid which was converted to the required Boc- or Fmoc-pro-tected derivatives (Scheme 2.7). 

After identification of A9-THC as the major active compound in Cannabis and its structural elucidation by Mechoulam and Gaoni in 1964 [66], a lot of work was invested in chemical synthesis of this substance. Analogous to the biosynthesis of cannabinoids, the central step in most of the A9-THC syntheses routes is the reaction of a terpene with a resorcin derivate (e.g., olivetol). Many different compounds were employed as terpenoid compounds, for example citral [67], verbenol [68], or chrysanthenol [69]. The employment of optically pure precursors is inevitable to get the desired (-)-trans-A9-THC. 

In an effort to develop easy-to-use ketoreductase toolbox , we have surveyed the activity and enantioselectivity of a collection of ketoreductases (KRED) from various sources toward the reduction of a variety of ketones [90,91]. These studies served as a useful guideline for developing enzymatic processes for the production of optically pure chiral alcohols. For example, several chiral chlorohydrins of pharmaceutical importance were synthesized in both enantiomeric forms using the enzymes in this ketoreductase collection (Table 7.2) [92]. Further applications of this collection and other commercially available ketoreductases can be found in a recent review [9]. 

A second example of the use of ionic chiral auxiliaries for asymmetric synthesis is found in the work of Chong et al. on the cis.trans photoisomerization of certain cyclopropane derivatives [33]. Based on the report by Zimmerman and Flechtner [34] that achiral tmns,trans-2,3-diphenyl-l-benzoylcyclopropane (35a, Scheme 7) undergoes very efficient (0=0.94) photoisomerization in solution to afford the racemic cis,trans isomer 36a, the correspondingp-carboxylic acid 35b was synthesized and treated with a variety of optically pure amines to give salts of general structure 35c (CA=chiral auxiliary). Irradiation of crystals of these salts followed by diazomethane workup yielded methyl ester 36d, which was analyzed by chiral HPLC for enantiomeric excess. The results are summarized in Table 3. 

Strikingly high stereoselectivities have been achieved in asymmetric syntheses with optically pure proline or proline derivatives, probably due to the rigidity of the five-membered ring. Other preferably used chiral auxiliaries include (S)-phenyl-alanine, (S)-valine and tert.-(S)-leucine. 

To validate our approach, we synthesized numerous 9-mer, 10-mer, and 12-mer peptides116 incorporating a series of optically pure cyclic- and open-chain a,a-... 

For the synthesis of optically pure building blocks we mainly focused on the synthesis of protected noncoded (R)- and (S)-amino acids, as they can be synthesized reliably in enantiomerically pure form with a large variety of side chains using asymmetric hydrogenation of a-amino-a, 3-didehydroamino acids using cationic diphosphine rhodium catalysts.216,217 As a typical example of a reactophore we present a-alkynyl ketones, which is a representative bis-acceptor molecule. In Scheme 5 are depicted some of the many synthetic applications of acetylenic ketones in heterocyclic synthesis, which have great potential for combinatorial and parallel organic synthesis. 

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