Cyclic terpenoid sulfides

The rest of the cyclic terpenoid sulfides are complex mixtures of partially degraded and isomerized derivatives of the terpenoid sulfides which elute on the capillary GC column as a broad, unresolved hump. On Raney nickel reduction this fraction yields a complex mixture of naphthenic hydrocarbons which cannot be resolved further by GC analysis. 

Branching of pathways is relevant in several cases. Thus, intermediates of the porphyrin biosynthetic pathway serve as precursors for chlorophyll (17, Fig. 2) and for the corrinoid ring systems of vitamin B12 (20, Fig. 2) (17). 1-Deoxy-D-xylulose 5-phosphate (43) serves as an intermediate for the biosynthesis of pyridoxal 5 -phosphate (39, Fig. 5), for the terpenoid precursor IPP (86) via the nonmevalonate pathway (Fig. 11), and for the thiazole moiety of thiamine pyrophosphate (46, Fig. 4). 7,8-Dihydroneopterin triphosphate (29, Fig. 3) serves as intermediate in the biosynthetic pathways of tetrahydrofolate (33) and tetrahydrobiopterin (31). The closely related compound 7,8-dihydroneopterin 2, 3 -cyclic phosphate is the precursor of the archaeal cofactor, tetrahydromethanopterin (34) (58). A common pyrimidine-type intermediate (23) serves as precursor for flavin and deazaflavin coenzymes. Various sulfur-containing coenzymes (thiamine (9), lipoic acid (7), biotin (6), Fig. 1) use a pyrosulfide protein precursor that is also used for the biosynthesis of inorganic sulfide as a precursor for iron/sulfur clusters (12). 

The Gassman method can also be applied to cyclic ketones and it has been applied to complex structures of the type encountered in terpenoid indole natural products <89JOC3449>. A modification of the Gassman method uses 2-(2-propylthio)ethyl acetate as the sulfide and leads to the formation of indoles without the need for desulfurization. After the rearrangement an elimination ensues, leading to cyclization and aromatization (Scheme 63) <92H(34)ioi7>. 

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