Cleavage sequences

Nucleophilic replacement of hydrogen on an isoxazole is unknown and replacement of substituents is discussed in Section 4.16.3.3. In this series it is difficult to identify reactions involving addition to the ring as, in many instances, they are rapidly followed by elimination or ring cleavage sequences. 

Oxidation of the alkaloid Glaucin (136) resulted in the formation of a yellow alkaloid 137, which seemingly is contained in Glaucium flavum var. vestitum (Scheme 48). Addition of methyl iodide converted this compound via a methylation/ether cleavage sequence into Corunnine (127) and small amounts of Pontevedrine (138) which is not a mesomeric betaine (71TL3093). 

The carbon-carbon double bond of an alkene 8 can be cleaved oxidatively, by a dihydroxylation reaction-glycol cleavage sequence ... 

Isolated double bonds can be oxidatively cleaved in systems containing a conjugated diene moiety if it is protected as a tricarbonyl(diene)iron complex44. Dienal 39 was acquired in 49% yield by a two-step osmylation-periodate cleavage sequence (equation 27). In contrast, ozonolysis of the polyene complexes is reported to lead to destruction of the complex. 

The strategy of designing saquinavir was based on the transition-state mimetic concept, an approach that has been used successfully in the design of potent inhibitors of renin and other aspartic proteases [10]. From the variety of nonscissile transition-state analogs of a dipeptide, the hydroxyethylamine mimetic was selected because it most readily accommodates the amino acid moiety characteristic of the Phe-Pro and Tyr-Pro cleavage sequence of the... 

Since alkoxysubstituted methyl cyclopropanecarboxylates like 66 undergo ring opening upon acid treatment to provide the y-oxoester 67, the cyclopropanation/ring cleavage sequence establishes an overall nucleophilic acylation of a,(5-unsaturated esters 40). 

Restriction enzymes are endonucleases which cleave specific sequences within double-stranded DNA stretches. The recognition and cleavage sequences of a routinely used group of endonucleases (called type 11 enzymes) may be four, five, six, or eight bases long and are symmetric across the two strands of DNA. Fig. 2.12 illustrates the cleavage specificity of a widely used sixbase-motif-specific endonuclease, EcoR 1. 

One of the most popular ways of using the double bond cleavage sequence envisages its utilization for the preparation of l, -dicarbonyl compounds via oxidation of the respective cycloalkene derivatives. Thus oxidation of cyclohexene represents the easiest way to prepare the 1,6-dialdehyde 460. Intramolecular aldol condensation of460 proceeds with ease to give the respective cyclopentene derivatives 461 or 462 (Scheme 2.149). 

Serine protease Natural substrate Cleavage sequence... 

Cyclopropanes and oxiranes can play an important role in initiation of olefin metathesis reactions via the formation of four-membered metallacycles and their subsequent cleavage sequences (13a, 13b). Conversely, the reverse of such reactions may sometimes be responsible for terminating a metathesis chain reaction. 

TABLE 4.2 Selected example of type II restriction endonucleases and their cleavage sequences. The recognition sequences of type II restriction endonucleases are shown with the arrow (4-) indicating the cleavage site... 

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