Diterpenes structures

The A group of vitamins are important metabolites of carotenoids. Vitamin A, (retinol) (Figure 5.70) effectively has a diterpene structure, but it is derived in mammals by oxidative... 

The diterpenes are C20 compounds biogenetically derived from geranylgeranyl pyrophosphate. The notable features of diterpene structures is the fascinating variation encountered in their skeletons and the occurrence in nature of both normal and antipodal stereochemical series. 

C20H32O, Mr 288.47, oil. A component of the defensive secretion of soldier insects of the termite subfamily Nasutitermitinae with a unique diterpene structure. Ut. Atta-ur-Rahman 1986,318-329-J. Am. Chem. Soc. 102, 6825 (1980). - [CAS 76649-58-6]... 

Representative diterpene structures are shown in Fig. 18. Diterpenes can be classified on a biogenetic basis (Ruzicka et al., 1953 McCrindle and Overton, 1965 Hanson, 1972a). There are a few open-chain diterpenes. Phy-tol, in an ester linkage, is found as a side chain on the chlorophyll molecule. Most diterpenes are cyclic compounds. A few diterpenes are formed by cy-clizations analogous to those involved in the synthesis of cyclohexanoid monoterpenes. The result is a macrocyclic structure such as that of cem-... 

As Taxol has a diterpenic structure, its biosynthesis starts in the formation of isopentenyl diphosphate (IPP) via the 2-C-methyl-D-erythritol 4-phosphate (MEP)... 

Smith C R, Madrigal R V, Weisleder D, Mikolajczak K L, Highet R J 1976 Potamogetonin, a new furanoid diterpene. Structural assignment by carbon-13 and proton magnetic resonance. J Org Chem 41 593-596... 

In Table 2, diterpene structures are identified by compound number and grouped with related structures belonging to the same skeletal type. The structural... 

The hypothetical C-8 carbonium ion resulting from this initial cyclization is stabilized by several alternative events (1) proton-loss yielding either the C-7-C-8 or C-8-C-17 double bond (e.g.. Figure 2), (2) neutralization via hydration or lactone or ether formation and (3) rearrangement. Much of the diterpene structural variability (Figure 3 [pp. 393-415]) is a consequence of the variety of rearrangement products resulting from this last mode of stabilization. 

These results suggest a clear distinction between the biogenetic steps associated with the cyclization processes (AB activity) and subsequent oxidative modifications. Although the extent to which gibberellin biosynthesis can be generalized to other diterpenes is unknown, the organization of its biosynthesis provides a useful framework for interpreting resin diterpene structural variability. 

The Gassman method has proven to be adaptable to complex structures, such as the intermediate 7.20B used in the synthesis of the indole diterpenes paspalicine and pasalinine[5]. Table 7.5 gives some other examples. 

The assumption of these conjugated double bonds makes possible a tetracyclic nucleus which accords with the suggestion previously made by the authors that these alkaloids might be structurally related to the diterpenes. It may also be noted that one of the nitric acid oxidation products of pseudaconitine has been recorded as unexpectedly giving a pyrrole reaction on destructive distillation. ... 

Mass spectrometry in structural investigation of diterpene alkaloids 97IZV1096. 

Fig. 5 Molecular structures of tyrosinase-active diterpene (8-10) and napelline (11, 12) type alkaloids [49]...

The GC-MS data (Figure 16.11) of the violet zone of B. carterii revealed that the unchanged diterpenes (verticillatriene, cembrene A, and cembrene C) and the nortriterpenes with carbohydrate structure originated from the pyrolyzed triterpenes (Figure 16.12) of the a- and (3-boswellic acids, named 24-norursa-3,12-diene (compound 7), 24-norursa-3,9(ll),12-triene (compound 8), 24-noroleana-3,12-diene (compound 9), and 24-noroleana-3,9(ll),12-triene (compound 10). 

Some representative Claisen rearrangements are shown in Scheme 6.14. Entry 1 illustrates the application of the Claisen rearrangement in the introduction of a substituent at the junction of two six-membered rings. Introduction of a substituent at this type of position is frequently necessary in the synthesis of steroids and terpenes. In Entry 2, formation and rearrangement of a 2-propenyl ether leads to formation of a methyl ketone. Entry 3 illustrates the use of 3-methoxyisoprene to form the allylic ether. The rearrangement of this type of ether leads to introduction of isoprene structural units into the reaction product. Entry 4 involves an allylic ether prepared by O-alkylation of a (3-keto enolate. Entry 5 was used in the course of synthesis of a diterpene lactone. Entry 6 is a case in which PdCl2 catalyzes both the formation and rearrangement of the reactant. 

This reaction can be used in synthesis of medium-sized rings by cleavage of specific bonds. An example of this reaction pattern can be seen in a fragmentation used to construct the ring structure found in the taxane group of diterpenes. 

NATURAL DITERPENE AND TRITERPENE QUINONE METHIDES STRUCTURES, SYNTHESIS, AND BIOLOGICAL POTENTIALS... 

Chemical Structures and Biological Activity of Natural Diterpene QMs... 

SCHEME 8.2 Chemical structures of various natural diterpene QMs. 

Another example of an efficient domino RCM is the synthesis of the highly functionalized tricyclic ring system 6/3-72 by Hanna and coworkers [252], which is the core structure of the diterpene guanacastepene A (6/3-73) (Scheme 6/3.21) [253]. Reaction of 6/3-71 in the presence of 10 mol% of Grubbs II catalyst 6/3-15 led to 6/3-372 in 93 % yield. Interestingly, the first-generation Ru-catalyst 6/3-13 did not allow any transformation. 

Scheme 6/3.21. Synthesis of the core structure of the diterpene guanacastepene A (613-73).

---