Skeletal types

Derivatives of the [2.2.1]-, [3.2.1]-, [4.2.1]-, and [5.2.1]-bicycloperoxides have been obtained in this way. In describing the results in detail, the expedient of subdividing the discussion according to skeletal type is less appropriate here than an approach based on the methods used to obtain the 3-bromocycloalkyl hydroperoxides 24 needed for the dioxabicyclization. 

The significance of the values calculated for the effective polarizability was first established with physical data, among them relaxation energies derived from a combination of X-ray photoelectron and Auger spectroscopy, as well as N-ls ESCA data53, 54). From our point of view, however, the most important applications of effective polarizability are to be found in correlating chemical reactivity data. Thus, the proton affinity (PA) of 49 unsubstituted alkylamines comprising primary, secondary and tertiary amines of a variety of skeletal types correlate directly with effective polarizability values (Fig. 22). 

In the following sections, we will review the marine isonitriles by skeletal types. This permits comparison of their differences and may suggest biogenetic clues. Skeletal frameworks are generally revealed by reducing the isonitrile with lithium/ethylamine to the corresponding hydrocarbon. Where trivial names have been assigned for skeletal types and for compounds, we shall use these as reported in the literature. In some cases, when structures related to previously mentioned compounds are discussed, formula numbers will be employed. 

The intermediacy of a carbocation or complex-equivalent is attractive, if one considers that the nucleophilic ambident cyanide ion may be accomodated on secondary or tertiary cationic sites. Where exceptions (e.g., 125,126,134-136 cf. Sect. 4.3) exist, the cationic intermediate resides on a primary allylic carbon. The following skeletal types are examples of some biogenetic schemes offered in conjunction with the structural determination of isocyanoterpenoids ... 

The nine skeletal types mentioned above are biosynthetically related, or conceivable proposals for their formation in vivo are accepted. A discussion on biogenetic relationships among indole alkaloids is outside the scope of this review and summaries on this subject can be consulted (7, 8, 13). 

More than 1500 triterpenoids have been discovered based on 40 skeletal types. Some examples include amyrin (produced by terrestrial plants), cephalosporin (synthesized by marine bacteria), and the steranes. The skeletal structure of the last contains three six-membered carbon rings and one five-membered ring (Figure 22.19a). 

This chapter follows the pattern of the previous Reports, with sections based on the major skeletal types of diterpenoid. The literature which has been covered is that available to August 1977. 

Kugler G, Weiss RG, Flucher BE, Grabner M (2004) Structural requirements of the dihydropyridine receptor alphal S II-III loop for skeletal-type excitation-contraction coupling. J Biol Chem 279 4721-4728. 

An anomalous X-ray scattering study of (+(-tubocurarine dibromide (73 4MeOH) confirmed the structure and absolute configuration earlier assigned. The N-N distance is 10.66 A (47,48). A purified sample of (+(-tubocurarine chloride (73a), prepared by selective quatemization of (+(-tubocurine (74) (Section V,B,1), gave the anomalous MS behavior previously ascribed to thermal disproportionation or the presence of impurities. In particular, the MS has mle 594 [17%, (M - 15)+, loss of Me] but also 608 (3.7%) and 622 (0.5%). The higher peaks seem to be due to a thermal Hofmann elimination followed by recombination with methyl radicals. Similar behavior is observed with the tertiary bases (—)-curine (75) and (+(-tubocurine (74), and may be general for alkaloids of this skeletal type (49). 

The knowledge of the key fragmentation routes of eburnamine and some related alkaloids confirmed or elucidated the structures of the alkaloids 11-methoxy-vincamine,100 vincaminine,102 and vinci-nine,102 of the same skeletal type as eburnamine. Alkaloids of the mavacurine-pleiocarpamine group (212)103 are characterized by a key fragment corresponding to the loss of the ester group and... 

In some cases it is even possible to deduce structures of unknown compounds without isolating them from a mixture. The spectrum of the crude mixture gives the molecular weight of the compounds present. If they are members of the same skeletal type, chemical... 

IR Spectroscopy. IR spectroscopy is a simple and rapid method of identifying functional groups and skeletal types in milligram samples of solid organic materials. Dispersive spectra have been used to determine the... 

The formation of this general type of bicyclic compound has been further developed by Dyke and co-workers49,76 into a synthesis of compounds with the skeletal structure (26) [Eq. (35)] and in this laboratory26 into a synthesis of the skeletal type (27) [Eq. (36)]. It is quite significant that these reaction sequences (acetal hydrolysis, ring closure, and displacement) were carried out both in concentrated acid49 76 and dilute acid26 and that no dehydration of the intermediate 4-hydroxy compound... 

Agrawal, P. K. Bishnoi, V. Studies on Indian medical plants. 42. Sterol and taraxastane derivatives from Artemisia annua and a rational approach based upon C-13 NMR for the identification of skeletal type of amorphane sesquiterpenoids. Indian J. Chem., 1996, 35B 86-88. 

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