4s configuration

N-Acetylneuraminic acid aldolase (or sialic acid aldolase, NeuA EC 4.1.3.3) catalyzes the reversible addition of pyruvate (2) to N-acetyl-D-mannosamine (ManNAc (1)) in the degradation of the parent sialic acid (3) (Figure 10.4). The NeuA lyases found in both bacteria and animals are type I enzymes that form a Schiff base/enamine intermediate with pyruvate and promote a si-face attack to the aldehyde carbonyl group with formation of a (4S) configured stereocenter. The enzyme is commercially available and it has a broad pH optimum around 7.5 and useful stability in solution at ambient temperature [36]. 

Comparable to the situation for the NeuA and KdoA enzyme pair (see above), a class I lyase complementary to the KDPGIc aldolase that has a stereopreference for the (4S)-configuration is known (Figure 10.11). The aldolase, which acts on... 

All statine analogs have the (3S,4S) configuration. ° dSta, 4-amino-6-methylheptanoic acid. 

As expected for the SAMP-alkylation, the (4S)-configuration was generated in excess. Thus, the absolute stereochemistry of (—)-serricornin (148) could be determined to be (4S,6S,7S). Other synthetic stereoisomers of serricornin prepared by Mori et al. 165) were almost devoid of pheromone activity. 

Scheme 2. Mechanistic analysis of reaction pathways for NeuA catalysis that considers the crucial influences of C-3 and anomeric configurations and of chair conformations on the three-point attachment of aldoses as acceptor substrates, Si-face attack leads to regular (4S)-configurated adducts while re-face attack leads to inverted stereochemistry (abbreviations anm = anomerization, inv = ring inversion)...

The Pseudomonas fluorescens KdgA was shown to accept several polar-sub-stituted aldehydes, albeit at rates much lower ( < 1%) than the phosphorylated natural substrate 12 (Table 3) [137]. Simple aliphatic or aromatic aldehydes were not converted. Synthetic utility and high stereoselectivity with unnatural substrates were demonstrated by conversion of both the D-configurated glycer-aldehyde (d-15) and lactaldehyde (d-16) to form the respective (4S)-configurated adducts 17 and 18 at the mmol scale. 

Much of our recent knowledge of the active centers of iron-sulfur proteins has come from the synthesis work of Holm (4) on analog compounds with 4Fe-4S, 2Fe-2S, and IFe centers. The additional ability to extract the iron-sulfur clusters from the proteins themselves and reinsertion of these clusters into other proteins has led to some interesting experiments which, among others, have shown that the 4Fe-4S configuration is more stable than the 2Fe-2S configuration. 

The novel compounds according to the present invention are substantially devoid of the undesired cannabis-type effects and can be used for the treatment of various diseases and disorders without undesired side-effects. As stated above, the novel compounds have an absolute stereochemistry at the 3- and 4-positions (terpene nomenclature) opposite to that of the natural series, i.e., they have a (3S,4S)-configuration. The compounds have a (-t-)-rotation of an absolute value approximately equal to that of the corresponding (-)-series compound. 

E20.13 (a) 4 s. You can approach this exercise in the way described in Section 20,2 for the d configuration (see Table 20.6). You first write down all possible microstates for the s configuration, then write down the Mi and iWj values for each microstate, then infer the values of Z and S to which the microstates belong. In this case, the procedure is not lengthy because there are only two possible microstates, (0") and (0 ). The only possible values of Mi and Ms are 0 and 1/2, respectively. If Mi can only be 0, then Z must be 0, which gives an S term (remember that L can take on all values Mi, (A4-1),. .., 0,. .. -Mi). Similarly, if Ms can only be +1/2 or -1/2, then S must be 1/2, which gives a multiplicity 25+1 -2. I herefore, the one and only term that arises from a 4s configuration is S. 

For class II DHAP-dependent aldolases, an ordered two-substrate mechanism has been derived from structural studies (Dreyer and Shulz 1996). DHAP binds the zinc ion with its hydroxyl and keto oxygen atoms, conducting to an enediolate intermediate, before the entrance of the acceptor aldehyde. For instance, FucA and RhuA are homotetramers with a Zn + atom in each subunit and the formed enediolate is linked to the carbonyl group of the acceptor aldehyde by either the si face (in the case of FucA) or the re face (in the case of RhuA). Thus, aldol addition products with 3R, 4R configuration are obtained in the case of FucA, and 3R, 4S configuration in the case of RhuA (Fig. 6.5.3). 

As mentioned above, the sodium coolant used by most LMR developers has created some safety concerns because of its chemical reactivity with air and water. Lead, lead-bismuth or other alloys of lead appear to eliminate these concerns because the chemical reactivity of this coolant with air and water is very low. The Russians have extensive experience with this coolant and, when combined with the Japanese 4S configuration, it conceptually is a very attractive system. Several major issues must be addressed, however, including what appears to be the most important materials corrosion. This is a serious issue, and although the Russians have had success in this area, long-term materials compatibility must yet be established. 

The electron configurations of certain elements appear to violate the rules we have just discussed. For example, Figme 6.31 shows that the electron configuration of chromium (element 24) is [Ar]3d 4s rather than the [Ar]3d 4s configuration we might expect. Similarly, the configuration of copper (element 29) is [Ar]3d 4s instead of [Ar]3d 4s. ... 

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