Initiation by fragmentation

Synthesis of octreotide and derivative thereof can be carried out by two methods. The first method is synthesized initially by fragment condensation solution phase procedures. The synthetic process of octreotide has been described by Bauer et al. (1). The second method is the synthese by solid-phase procedures. Edward et al. (2) isolated side chain protected octreotide with a total yield of 14% by cleaving the protected peptide from the resin with threoninol. Arano et al. (3) carried out another solid phase method for octreotide, and produced it in overall 31.8% yield based on the starting Fmoc-Thr(tBu)-ol-resin. The basic difference from the other procedures already described is that the introduction of the threoninol is carried out upon the protected peptidic structure (resin-free), which, when appropriately activated, leads quantitatively and without needing to make temporary protections upon the threoninol, to the protected precursor of octreotide, which in turn, with a simple acid treatment leads to octreotide with very high yields. 

Acyl radicals can fragment with toss of carbon monoxide. Decarbonylation is slower than decarboxylation, but the rate also depends on the stability of the radical that is formed. For example, when reaction of isobutyraldehyde with carbon tetrachloride is initiated by t-butyl peroxide, both isopropyl chloride and isobutyroyl chloride are formed. Decarbonylation is competitive with the chlorine-atom abstraction. 

If failure is initiated by corrosion or impact of a missile or fragment, it can be assumed that failure pressure will be the normal operating pressure. 

BromophenyI Enynes with Initiation by tert-RutyUithium and Sulfur (Fragments Arene C=C C = C and S)... 

II is via penetration of hot combustion products into the existing pores of the expl. Propagation in Region III is via convective flow between the charge surface and its confinement. This regime is claimed to be affected by confinement expansion (due to pressure), and by fragmentation of the peripheral portions of the expl column. The phenomena in Regions IV and V have already been described in Section VIII under Initiation by Impact Friction... 

Seven-membered carbocycles are also available from the reaction of alkenylcarbene complexes of chromium and lithium enolates derived from methyl vinyl ketones [79b] (Scheme 65). In this case, the reaction is initiated by the 1,2-addition of the enolate to the carbene complex. Cyclisation induced by a [1,2]-migration of the pentacarbonylchromium group and subsequent elimination of the metal fragment followed by hydrolysis leads to the final cyclo-heptenone derivatives (Scheme 65). 

Thus the reactant ions for chemical ionization formed in the methane plasma consists of approximately equal amounts of a strong gaseous Bronsted acid (CH5+) and ions which can act either as Lewis acids or Bronsted acids (C2H5+ + C3H5+). These reactant ions will effect the chemical ionization with an added substance by proton transfer or hydride ion transfer, both of which may be accompanied by fragmentation of the ion initially formed. 

Only fragmented data are available on polymerization of other methacrylates. Propagation constants and the respective Arrhenius parameters for the homopolymerization of various methacrylates initiated by sodium metallo-organics were reported recently +3,56) and are given in Table 2. 

Hydrolysis of RNA by alkali or pancreatic RNase leads initially to fragments which terminate in 2, 3 -cyclic phosphodiesters. Micrococcal nuclease, on the other hand, gives rise to fragments terminating in 3 -phos-phomonoester groups which facilitate their isolation, and this enzymic hydrolysis has been used to prepare 3 -ribodinucleotides. ... 

The reaction can occur by a concerted fragmentation process initiated by a two-electron oxidation. 

Scheme 8.4. Dioxetane fragmentation initiated by enzymatic ester hydrolysis.

The ratio of the amount of n-butane-2-13C to the amount of isobutane produced was, provided measurements were made under conditions where secondary reactions were unimportant (i.e., initial reaction products), constant and independent of temperature, and this ratio was 1/4. At the same time, no scrambling of the 13C occurred i.e, all of the isotopically substituted molecules remained singly labeled. Anderson and Baker (68) speculated that the butane isomerization might have occurred by a recombination of adsorbed surface residues produced by fragmentation of the... 

In the second dual photo/thermal initiation strategy, the approach described above is augmented by the inclusion of a thermal initiator. Upon illumination, active centers produced by fragmentation of the photoinitiator start the polymerization reaction. The heat evolved from the exothermic photopolymerization elevates the temperature of the system and results in the production of additional active sites by the thermal initiator. This dual initiating strategy provides both the cure on demand (temporal control) afforded by photopolymerization, and the completeness of cure provided by the thermal initiator. 

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