Transformation efficiency, effect

Catalytic olefin metathesis, in only a few years, has risen to be one of the most important and reliable processes in organic synthesis. Recently, several reports by Schrock and Hoveydallsbbond forming transformations efficiently and enan-tioselectively. A recent concise and enantioselective synthesis of exo-brevicomin by Burke utilizes chiral catalyst 91 (Scheme 13) to effect the desymmetriza-tion of 90 through a ring-closing metathesis.11531... 

The byproduct sitosterol was for many years quite useless due to the lack of a chemical point of attack on the side chain that would permit its removal. Extensive efforts on the part of many laboratories eventually led to the discovery of a pseudomonas microbe that efficiently effected that transformation. Fermentation of (4-1) digests the entire aliphatic side chain at 17 to afford a mixture of 17-keto products including dehydroepiandrosterone (4-2) [4]. 

Ohse, M., K. Kawade, and H. Kusaoke. 1997. Effects of DNA topology on transformation efficiency of Bacillus subtilis ISW1214 by electroporation. Biosci. Bio-technol. Biochem. 61 1019-1021. 

Lithium tetrafluoroborate efficiently catalyzes the cyclization of n-hydroxybenzaldimines 469 with 3,4-dihydro-277-pyran 455 at ambient temperature to afford a class of pyrano derivatives representated by 470 in excellent yields with high diastereoselectivity (Equation 34) <2001TL6381>. The use of catalytic indium trichloride and phospho-nium perchlorate has been found to efficiently effect the same transformation <2002T10301>. 

Between the methods of Agrobacterium and microprojectile transfer, nearly every plant species can be transformed effectively [35]. However, these methods are covered by patent claims and may result in limited transformation efficiency for some cell types. For this reason, the use of alternative gene-transfer methods is an active area of research for all cell types. Alternative gene-transfer techniques include electroporation, microinjection, liposome fusion, direct transfer into protoplasts, and laser treatment [38]. In electroporation, DNA is transferred into the cell using a high-voltage electrical pulse [39]. Standard... 

Generally, hypervalent iodine reagents are often better than traditional reagents of similar reactivity, with respect to efficiency and chemoselectivity - sometimes even stereoselectivity. Unusual reactivity is another interesting feature which has often resulted in unexpected transformation. Examples of such reactions may be found in the oxidation of nitrogen-containing compounds, the Hofmann rearrangement in acidic conditions, the acetalization of carbonyl compounds in alkali, the remote functionalization of steroids, etc. Some unique transformations were effected in the... 

The next important property of PolyP-PHB complexes is their effect on DNA transfer into bacterial cells. It was the striking correlation between PolyP-PHB concentrations and transformation efficiencies in Azotobacter vinelandii, Bacillus subtilis and E. coli that led Reusch and Sadoff (1988) to postulate that the complexes are involved in DNA transmembrane transport. 

The effect of four ORFs on the transformation efficiency of the shuttle-vector was examined by introducing various deletions into these ORFs. Figure 2 shows the effects of the deletions in ORF943 on the transformation efficiency of the shuttle-vector. When the deletions were introduced into ORF943 from 5 side, the transformation efficiency decreased stepwise, indicating that this ORF plays an important role in the maintenance of shuttle-vectors in cyanobacterial cells. 

The other ORFs, ORF64, ORF71, and ORF93 showed no significant effect on the transformation efficiency of this shuttle-vector (data not shown). From these results the simplified shuttle-vector pAQJ4 with full ORF943 was constructed from the pAQJ6 vector (Fig. 1). 

Figure 2. Effects of the deletion in ORF943 on the transformation efficiency of shuttle-vectors...

Corey s group subsequently developed a novel and more efficient conversion of racemic 5-HPETE to racemic LTA4 methyl ester. It was found that allylic hydroperoxides undergo a remarkable intramolecular rearrangement upon treatment with trifluoroacetic anhydride to produce epoxy alcohols in high yields. Standard transformations then effected the conversion of this intermediate to racemic LTA4 methyl ester. 

Attempts to effect this transformation efficiently have not been very successful. Mono-or dlfunctlonal living poly THF was prepared using the appropriate cationic Initiator and subsequently reacted with the sodium salt of clnnamyl alcohol or of l-phenyl-l-buten-4-ol to yield styryl groups on terminal ligands (Equation 8) In which n > 1 or 2 respectively (11). In both cases reaction was shown to... 

Recently, a palladium complex coordinated with an axially chiral, monoden-tate phosphine ligand, MeO-MOP (7a) or its analogs [21], has been reported to be highly effective for the enantioselective hydrosilylation of alkyl-substituted terminal olefins (Scheme 4) [22,23]. Simple terminal olefins 8 were transformed efficiently into the corresponding optically active 2-alkanols 11 with enantiose-lectivities ranging between 94% and 97% ee by the catalytic hydrosilylation-ox-... 

In our study, we analyzed the effect of various chemicals capable of enhancing the HR frequency (HRP) prior to transformation. We found that these chemicals can also improve transformation efficiency. We have developed a system that allowed identification of growth media compositions that influence HRF. We have demonstrated the ability of such modified growth media to improve the transformation frequency. 

Organism Genetic modification Vector Transformation method Selection ) Counterselection ) Effective transformation efficiency ) (CFU/pgDNA) References VI 3... 

PHA production uses strain development, shake flask optimization, lab and pilot fermentor studies, and industrial scale up (Figure 3.6). Effective microbial production of PHAs is dependent on a variety of factors, which include the final cell density, bacterial growth rate, percentage of PH A in cell dry weight, time taken to reach high final cell density, substrate to product transformation efficiency, price of substrates and a convenient and cheap method to extract and purify the PHAs (Figure 3.6). 

Selection of the right reagent for a reaction is made on the basis of efficiency, availability and its effect on environment. The selection of a particular reagent versus another reagent for the same transformation can effect the nature of by-products, percentage yield etc. (see Chapter 6 for details). 

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