Cyclic compounds ring assemblies

The overall topology of the structure is specified as follows. A neutral chain compound is called catena preceded by a multiplicative prefix, di , tri , etc., to indicate the number of branches in the molecule. Likewise, cyclic compounds are called cycle preceded by the appropriate multiplicative prefix. A mixed chain and ring compound is classified as an assembly composed of acyclic and cyclic modules and, if neutral, is named as catenacycle , with appropriate multiplicative prefixes inserted as in Example 3 below. 

Enniatins A (also called lateritiin I) (Fig. 2), B, C, D, E, and are antibiotics synthesized by various strains of the genus FusariumP Like valinomycin, they are cyclic compounds, but they differ in several respects. First, the enniatins are cyclohexadepsipeptides, so they are half the size of valinomycin. Second, their ring nitrogen atoms are methylated. In contrast to valinomycin, they show poor ion selectivity. The prototype of this family is enniatin B, a cyclohexadepsipeptide assembled by threefold repetition of the L-N-methylvaline D-hydroxyisova-leric acid subunit. When t-A-methylvaline is replaced by L-N-methylphenylalanine in this repeating sequence, beauvericin results. 

Ionic (electrostatic) interaction may also lead to cyclic self-assembly. Numerous alkah metal and alkahne-earth molecular compounds fall into this category. These include three types of associated ring compounds ... 

Pseudorotaxanes are interlaced compounds in which a filamentous ligand is threaded through a cyclic one. Their one-step synthesis by self-assembly generally involves a rings-and-strings ... 

Tri-, tetra- to polycyclic compounds (part B) appear in the structural formula index in order of ring size (carbocyclic before heterocyclic ring compounds) under appropriate compound headings. Part C contains spiro compounds with similar ordering followed by part D which contains assemblies of identical cyclic systems (c.g., bicyclopropyl). 

A number of steps are required for the conversion of rac-12 into the cyclic hemiacetal rac-14 (Scheme 3). This compound is important to the rest of the synthesis, since it cannot only be prepared from tryptamine (3) and dimethyl 2-ketoglutarate (4), but can also be obtained readily in substantial amounts and in enantiomerically pure form by degradation of strychnine. As soon as enough of this relay hemiacetal has been secured, assembly of the G ring can be tackled. 

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