Degradative studies

Chemical degradation studies carried out on streptovaricias A and C, which are the primary components of the cmde complex, yielded substances shown ia Figure 1. Streptovaricia A (4), consumes two moles of sodium periodate to yield variciaal A [21913-68-8] (1), 0 2 200, which accounts for the ahphatic portion of the molecule, and prestreptovarone [58074-37-6] (2), C2C)H2C)N02, which accounts for the aromatic chromophore of the streptovaricias (Fig. 2). Streptovaricia G (9) is the only other streptovaricia that yields prestreptovaroae upoa treatmeat with sodium periodate. Treatmeat of streptovaricias A (4), B (5), C (6), E (8), and G (9) with sodium periodate and osmium tetroxide yields streptovarone [36108-44-8] (3), C24H23NO2, which is also produced by the reaction of prestreptovarone with sodium periodate and osmium tetroxide (4,65). A number of aliphatic products were isolated from the oxidation of streptovaricia C and its derivatives (66). 

Naphthoquiaomycias A (67) and B (68) are isolated from Streptomyces S-1998 (223) and the stmctures for (67) and (68) assigned on the basis of spectral data. Naphthoquiaomycias A and B inhibit fatty acid synthesis ia E. coli. Actamycia (69) is obtaiaed from Streptomyces sp. EJ784 and its stmcture arrived at on the basis of spectral data and degradation studies (224,225). 

Chain Structure. The chemical composition of poly (vinyhdene chloride) has been confirmed by various techniques, including elemental analysis, x-ray diffraction analysis, degradation studies, and in, Raman, and nmr spectroscopy. The polymer chain is made up of vinyhdene chloride units added head-to-tail ... 

Vitamin E was first described ia 1922 and the name was originally applied to a material found ia vegetable oils. This material was found to be essential for fertility ia tats. It was not until the early 1980s that symptoms of vitamin E deficiency ia humans were recognized. Early work on the natural distribution, isolation, and identification can be attributed to Evans, Butt, and Emerson (University of California) and MattiU and Olcott (University of Iowa). Subsequentiy a group of substances (Eig. 1), which fall iato either the family of tocopherols or tocotrienols, were found to act like vitamin E (1 4). The stmcture of a-tocopherol was determined by degradation studies ia 1938 (5). 

Curamycin. Curamycin A, presented in Table 2, is the primary component of the culture Streptomjces curacoi (21) and preliminary chemical degradation studies (18) estabUshed it to be an oligosaccharide antibiotic. Later when the complete stmcture was assigned (17,19), the close relationship to flambamycin was evident. Curamycin A melts at 192—199°C. 

The pigment was first described in 1866 (47). Based on degradative studies and chemical reactions, it was proposed that lapacol was the alkenyUiydroxynaphthoquinone (7) (48), but it was later deterrnined that its stmcture is actually (8) (49). 

All of these methods provide only moderate yields of 17-keto steroids, but some [particularly (b)] have been considered for large scale preparative work. The advent of superior methods now limits the above procedures to structure proof and degradative studies. 

Oxidation of ecgonine (2) by means of chromium trioxide was found to afford a keto acid (3). This was formulated as shown based on the fact that the compound undergoes ready themnal decarboxylation to tropinone (4)The latter had been obtained earlier from degradative studies in connection with the structural determination of atropine (5) and its structure established independently. Confirmation for the structure came from the finding that carbonation of the enolate of tropinone does in fact lead back to ecgonine. Reduction, esterification with methanol followed by benzoylation then affords cocaine. 

An isomeric sugar, D-javose, is a constituent of two cardenolide glycosides (strophanthojavoside and antiarojavoside) found (42) in the seeds of Antiaris toxicaria Lesch. Degradative studies indicated (42) that javose had the structure 6-deoxy-2-0-methyl-D-allose (17) and this assignment was confirmed by two stereospecific syntheses. 

Thermal degradation studies of EB-cured terpolymeric fluorocarbon rubber [430] by nonisothermal thermogravimetry in the absence and presence of cross-link promoter TMPTA reveal that thermal stability is improved on radiation and more so in the presence of TMPTA. Initial decomposition temperature, maximum decomposition temperature and the decomposition... 

The polyene macrolide filipin was isolated in 1955 from the cell culture filtrates of Sterptomyces filipinensis, and was later shown to be a mixture of four components [36]. Although too toxic for therapeutic use, the filipin complex has found widespread use as a histochemical stain for cholesterol and has even been used to quantitate cholesterol in cell membranes [37]. The flat structure of filipin III, the major component of the filipin complex, was assigned from a series of degradation studies [38]. Rychnovsky completed the structure determination by elucidating the relative and absolute stereochemistry [39]. The total synthesis plan for filipin III relied heavily on the cyanohydrin acetonide methodology discussed above. 

Considering the high hydrophobicity of the palmitoyl side chain and the rigidity of the polymer backbone, we assumed that poly(N-palmitoylhydroxyproline ester) would degrade somewhat more slowly than poly (lactic acid) or polycaprolactone. In order to confirm this hypothesis, a series of long-term stability and degradation studies have been performed over the last 2 years at MIT (22). 

Synthetic studies of validamycins were initially devoted to establishing the structure of validamycin A. The structure in which a ) -D-glucopyranosyl group is attached to 0-3 of the validamine residue was initially proposed on the basis of degradative studies. However, the original structure was re-... 

Since the present study aims at carrying out the investigation of the break-down phenomenon and searching for the possible mechanism of the phenomenon, we have chosen the similar condition as in [1] for the wall shear stress to induce break-down The reference temperature in the degradation studies was 60 °C. This value may be lower than the value used in a typical DHS. In a low-pressure system, however, it was necessary to use lower the temperature to avoid the formation of bubbles. For parametric studies, one of the variables was varied while the other variables were fixed at the reference condition (Tanperature 60 °C Re 8,000 Surfactant concentration 200ppm Volume of solution charged 0.010 m ). 

Analysis of the MHR by high-performance size-exclusion chromatography (HPSEC) revealed three distinct populations to be present, which were isolated on a preparative scale. The composition of the populations differed mainly in the relative proportion of rhamnose, xylose and the amount of methyl esters and acetyl groups, although the general characteristics were rather similar (Table 2). However, degradation studies with RGase showed that, in contrast... 

---