Leaves asymmetric

Before leaving asymmetric hydrogenation reactions, we should mention one other related process that has acquired immense importance, again because of its industrial application. You have come across cit-ronellol a couple of times in this chapter already the corresponding aldehyde citronellal is even more important because it is an intermediate in the a synthesis of L-menthol by the Japanese chemical company Takasago. Takasago manufacture about 30% of the 3500 ton annual worldwide demand for L-menthol from citronellal by using an intramolecular ene reaction (a cycloaddition you met in Chapter 35). 

We now leave asymmetric reductions and move on to two asymmetric oxidations, which are probably the two most important asymmetric reactions known. They are both products of the laboratories of Professor Barry Sharpless. 

The negatively charged phospholipid phosphatidylserine is asymmetrically distributed in mammalian cell membranes, primarily on the inner leaflet. Upon exposure to collagen or thrombin, the distribution of phospholipids changes with increasing phosphatidylserine in the external membrane leaf (I). The increased expression of phosphatidylserine on the outer leaflet of the membrane creates a procoagulant surface on which several steps of the coagulation cascade take place. 

In Chapter 10 we saw that there are various methods for the analysis of categorical (and mostly binary) efficacy data. The same is true here. There are different methods that are appropriate for continuous data in certain circumstances, and not every method that we discuss is appropriate for every situation. A careful assessment of the data type, the shape of the distribution (which can be examined through a relative frequency histogram or a stem-and-leaf plot), and the sample size can help justify the most appropriate analysis approach. For example, if the shape of the distribution of the random variable is symmetric or the sample size is large (> 30) the sample mean would be considered a "reasonable" estimate of the population mean. Parametric analysis approaches such as the two-sample t test or an analysis of variance (ANOVA) would then be appropriate. However, when the distribution is severely asymmetric, or skewed, the sample mean is a poor estimate of the population mean. In such cases a nonparametric approach would be more appropriate. 

Figure 3.10 Natural product synthesis imploying SAMP-RAMP hydrazones 5-(+)-4-methyl-3-heptanone, the leaf cutting ant alarm pheromone [105] serricornin, the sex pheromone of the cigarette beetle [120] S,E-4,6-dimethyl-6-octen-3-one, the defense substance of daddy longlegs [120] (+)-eremophilenolide [120] and antibiotic X-14547A [121], Stereocenters formed by asymmetric alkylation are indicated by. ...

Alkylation of lithiated hydrazones forms the basis of an efficient method for the asymmetric alkylation of aldehydes and ketones, using the optically active hydrazines (5)-l-amino-2-(methoxymethyl)pyrroUdine (SAMP) 59 and its enantiomer (RAMP) as chiral auxiliaries. Deprotonation of the optically active hydra-zones, alkylation and removal of the chiral auxiliary under mild conditions (ozonol-ysis or acid hydrolysis of the A-methyl salt) gives the alkylated aldehyde or ketone with, generally, greater than 95% optical purity. This procedure has been exploited in the asymmetric synthesis of several natural products. Thus, (S)-4-methyl-3-heptanone, the principal alarm pheromone of the leaf-cutting ant Am texana, was prepared from 3-pentanone in very high optical purity as shown in Scheme 1.74. 

Fig. 5. Plant of Phaseolus vulgaris which was decapitated, supplied with 200 jaM lAA and grown at 1/3 atmosphere. The lateral buds in the axils of the primary leaves have grown out asymmetrically. One primary leaf was removed for the photograph, taken after 12 days.

---