Hypothetical biogenesis

When synthesizing a natural product, try to follow the known or hypothetical biogenesis. 

Scheme 10 Hypothetical biogenesis of lycodine and phlegmarine-type alkalooids...

An alternative to the aromatic amino acids hypothesis is one which invokes their proximate precursor, viz. a hydrated prephenic acid in which the potential ring E of yohimbine is already in a reduced state and has in addition the carboxyl. An important conclusion arising out of this theory was the prediction of a uniform stereochemistry in indole alkaloids of Type I at the carbon equivalent C-15 of yohimbine. This hypothetical biogenesis—the prephenic acid theory is Ulustrated in Chart 2.3. 

Fe-S complexes have important functions in today s living systems, in enzymes such as the ferredoxins and oxidoreductases, as well as in electron transport proteins. It is striking that these redox reactions mainly involve elements and compounds such as CO, H2 and N2, which were probably also components of the primeval Earth s atmosphere. Thus, the assumption of an active involvement of Fe-S clusters in a (hypothetical) Fe-S world in processes which finally led to biogenesis appears completely reasonable We now have a background to the theory of the chemoau-totrophic origin of life . 

UV radiation hypothetical, but so is the transport of molecules from outer space to Earth. Recent analyses of the Murchison meteorite by two scientists from the University of Arizona, Tucson (Cronin and Pizzarello, 1997 Cronin, 1998) have shown it to contain the four stereoisomeric amino acids DL-a-methylisoleucine and DL-a-methylalloisoleucine. In both cases, the L-enantiomer is present in a clear excess (7.0 and 9.1%). Similar results were obtained for two other a-methyl amino acids, isovaline and a-methylvaline. Contamination by terrestrial proteins can be ruled out, since these amino acids are either not found in nature or are present in only very small amounts. Since the carbonaceous chondrites are thought to have been formed around 4.5 billion years ago (see Sect. 3.3.2), the amino acids referred to above must have been subject to one or more asymmetric effects prior to biogenesis. 

A hypothetical biosynthetic sequence has been proposed for the 3-alkyl-2,6-dimethylpyrazines (482) from various species of Odontomachus ants, as shown in Scheme 65. The acyloin (507), prepared by condensation of the pyruvate with active acetate, or the derived dione (508) may condense with the amide (509) of alanine, ultimately giving the 3-alkyl-2,6-dimethylpyrazines (482) (141). A separate biogenesis is envisaged for the 3-alkyl-2,5-dimethylpyrazines (481) such as 3-isopentyl-2,5-dimethyl (20h) and 2,5-dimethyl-3-styrylpyrazines (20j,... 

A hypothetical sequence, based mainly on the reported isolation of cMvsergyl-L-valine methyl ester from rye ergot (18) was proposed by Agurell (58). According to him, the biogenesis of ergotamine (68) can be represented as follows ... 

The possible origins of highly conjugated lactam groups has been discussed above in connection with the biogenesis of dielsiquinone (134). Similar considerations may be applicable to dielsine (137), dielsinol (138), and 2,7(or 6)-dimethoxy-6(or 7)hydroxyonychine (166, 167). In the case of the latter compound, as with dielsiquinone, the methoxyl group at C-2 can be traced back to a hypothetical 4-methoxylated aporphinoid precursor. 

Fig. 12.5. Biogenesis and assembly of cytochrome 6-c, complex in the inner mitochondrial membrane. Cytochrome fc-Cj complex contains at least five different subunits COREI (corl), COREII (corll), nonheme iron protein (Fe-S), cytochrome c, (cyt Cj), and cytochrome b (cyt b). Cytochrome f> is a mitochondrial gene product and is probably assembled into the inner membrane (IM) via vectorial translation by mitochondrial ribosomes. The other subunits are synthesized on cytoplasmic ribosomes as larger precursors. The precursors, perhaps in association with a cytoplasmic factor , are attached to receptors on the mitochondrial outer membrane (OM). The complex laterally diffuses to the junctions of the outer and inner membranes, and with the help of a hypothetical translocator the precursors are imported across the membrane. Pre-Corl, pre-Corll, and the pre-nonheme iron protein cross the two membranes, whereas cytochrome c, becomes anchored to the outer face of the inner membrane, facing the intermembrane space (IMS). Cytochrome b is assembled inside the inner membrane, and the nonheme iron protein and Corl and Corll are assembled into the matrix side of the inner membrane. The N-terminal extensions are removed by a soluble matrix protease. The N-terminal extension of cytochrome c, is removed in two steps the first is catalyzed by the matrix protease and the second probably by a protease located on the outer face of the inner membrane.

Fig. 11.4 Hypothetical model for integration of the major mechanisms of TAG storage and mobilization (1) conversion of fibroblasts/ preadipocytes into adipocytes, (2) biogenesis of forming LD at the ER membrane, (3) fusion of smaller LD to mature LD, (4) translocation of HSL from the cytosol to the surface of LD, (5) disassembly and reorganization at...

The biogenesis of this complex and highly oxygenated steroids (8 rings) containing a minimum of nine oxygen atoms calls for an elaborate system on the part of the plant. These were mainly formed in Physalis species, not in the other Solanaceous plants. A hypothetical biogenetic scheme, (Chart IV) was proposed by Crombie et al. . ... 

Fig. 22.—The Hypothetical Model Proposed by Miihlethaler for Biogenesis of Cellulosic Elementary Fibrils. "...

Figure 33 Biogenesis of some of the hexose-, pentose-, and cyclitol-derived components in ACAGAs from 6-IC I-D-giucose (according to Ref. 8). The labeling patterns in neomycin and vali-damycin measured by nuclear magnetic resonance (NMR) prove that all units are built up preferentially from C, (circled C atoms), C. or C, units (thick lines) rearranged by transketolase-and transaldolase-catalyzed reactions in passages through the pentosephosphate cycle. The paiiem in Cal products is hypothetical. The positions derived from the C6 of D-glucose are marked by a star.

Winter A (1966) A hypothetical route for the biogenesis of lAA. Planta 71 229-239 Wright STC (1961) A sequential growth response to gibberellic acid, kinetin, and indolyl-acetic acid in the wheat coleoptile. Nature 190 699-700 Zimmerman DC, Coudron CA (1979) Identification of traumatin, a wound hormone, as 12-oxo-trans-lO-dodecanoic acid. Plant Physiol 63 536-541... 

Fig. 1. A tentative scheme of adrenal steroid biogenesis with a hypothetical central role for 3/3-hydroxy-A°-steroids and their sulfates. Encircled symbols indicate secreted compounds = androstenedione P = progesterone B = corticosterone F = cortisol.

These compounds are not aromatic, because the aromatic ring has been oxidized to an epoxide (67). The biogenesis of these cyclohexane-epoxides remains to be solved, although hypothetical pathways involving an arene oxide have been proposed (43, 57). 

Embodied in the hypothetical scheme of biogenesis Figure 5.11) which has evolved to describe the modes of biosynthesis of the various Cg. C, plant phenols, are related proposals which have been discussed to explain the origins of the various Cg. C2 and Cg compounds which occur in nature. Neither of these two groups of phenols is particularly common and definitive biosynthetic studies have therefore been few. 

In the following discussion, diterpene biogenesis is described in terms of a hypothetical reaction sequence leading from an appropriate labdane precursor to a product representative of one of the 103 skeletal types reported from the Compositae. These skeletal types are arranged in Figure 3 according to their putative biogenetic relationship. 

Fig. 3. Hypothetical scheme for the biogenesis of mould products formally derived from seven acetate units. Denotes atoms derived from COgH of an acetate unit...

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