Nucleus isolation

In fact, if the nucleus isolated from the cell of one animal is injected into the enucleated egg from another animal of the same species and the egg is implanted in a foster mother, the resulting offspring is a clone of the animal from which the nucleus was derived (Fig. 17.13). Clones of sheep and pigs have been produced, and similar techniques could be used to clone humans. Obviously, these experiments raise many ethical questions that will be difficult to answer. 

Fig. 3 Isolation of nuclei from suspension tissue culture cells. (A) Low-power SEM image of nucleus isolated from K.S62 tissue culture cell, after isolation and Percoll density-gradient purification. This particular nucleus shows surface indentations due to its position in the cell cycle (approaching prophase), but the overall surface morphology of the nuclear envelope is largely free of cytoplasmic contamination, and numerous pore complexes (arrowed) arc apparent. Scale bar, 1.0 /u,m. (B) Detail of A, showing cytoplasmic surface of the nuclear envelope with clearly visible nuclear pore complexes, and a typical density of ribosomes (remember the outer nuclear envelope is the innermost element of the rough endoplasmic reticulum). Scale bar, 125 nm.

Figure 19.110 Examples of polychlorinated amides with a thiazole nucleus isolated from Dysidea species.

The catalyst is inactive for the hydrogenation of the (isolated) benzene nucleus and so may bo used for the hydrogenation of aromatic compounds containing aldehyde, keto, carbalkoxy or amide groups to the corresponding alcohols, amines, etc., e.g., ethyl benzoate to benzyl alcohol methyl p-toluate to p-methylbenzyl alcohol ethyl cinnamate to 3 phenyl 1-propanol. 

Two moles of /3-alkoxyaicene can condense on each other by means of their a- and /3-carbon atoms. The resulting intermediate reacts on the anhydrobase by elimination of a molecule of ethanol resulting in a neocyanine formation (Schemes 59 and 60). Both monoanilino and bis-anilino derivatives resulting from the condensation of dimethylform-amide have been isolated. They are capable of furnishing various condensations on either ketomethylene or another reactive nucleus (Scheme 61). 

Although many sterols and bile acids were isolated in the nineteenth century, it was not until the twentieth century that the stmcture of the steroid nucleus was first elucidated (5). X-ray crystallographic data first suggested that the steroid nucleus was a thin, lath-shaped stmcture (6). This perhydro-l,2-cyclopentenophenanthrene ring system was eventually confirmed by the identification of the Diels hydrocarbon [549-88-2] (4) and by the total synthesis of equilenin [517-09-9] (5) (7). 

Subsequently, other structural variations were reported encompassing compounds such as PS-5 (5) (5), carpetimycin A (6) (6), asparenomycin A (7) (7), and pluracidomycin A (8) (8), from a wide variety of streptomycete strains. Following these stmctures the simplest member of the series, having the completely unsubstituted nucleus, (1, X = CH2), was isolated from bacterial strains of Serratia and Ervinia (9). AH other natural products reported have substituents at both the C-6 and C-2 positions of the bicycHc ring system. Differences in the nature and stereochemistry of these substituents has provided a wide variety of stmctures, and over forty variations have been reported and comprehensively Hsted (10). 

The sulfated compounds MM 13902 (3, n = (5) and MM 17880 (4) are also broad-spectmm agents, but not as potent as thienamycia and all lack any significant activity against Pseudomonas (73). Many carbapenems are excellent inhibitors of isolated P-lactamases, particularly the olivanic acid sulfoxide MM 4550 (3, n = 1) (3). The possible mechanism of action of the carbapenems as inhibitors of P-lactamases has been discussed in some detail (74). Other carbapenems such as PS-5 (5) (75), the carpetimycins (76), asparenomycins (77), and pluracidomycins (8) are all highly active as antibiotics or P-lactamase inhibitors. The parent nucleus itself (1, X = CH2) is intrinsically active, but chemically unstable (9). 

With certain 6-substituents on the penam nucleus, it has been possible to isolate sulfonium derivatives (Scheme 16) (79JCS(P1)3175). As expected, these are highly reactive compounds. 

Many selective epoxidations are possible with polyunsaturated steroids. In general, oc, -unsaturated ketones are not attacked by peracid, although linear dienones react slowly at the y,5-double bond. Aw-Chloroperbenzoic acid is the reagent of choice for this reaction.When two isolated double bonds are present in the steroid nucleus, e.g. (27) and (30), the most highly substituted double bond reacts preferentially with the peracid. Selective epoxidation of the nuclear double bond of stigmasterol can likewise be achieved.However, one exception to this general rule has been reported [See (33) (34)]. ... 

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