Ring templates

The first total synthesis of erythronolide B (1) by Corey stands as an event of great historical significance in synthetic chemistry it provides a powerful illustration of the utility of Corey s methods of macrolactonization and it demonstrates, in a particularly insightful way, the value of using readily accessible six-membered ring templates for the assembly of contiguous arrays of stereo-genic centers. 

Inhibitor Design Using Five-Membered Ring Templates... 

Fig. 7.7 Ring templates for cyclohexane (left) and cyclohexene (right) together with their associated internal energies.

The ring templates can be further used to construct larger, multicyclic systems as illustrated in Fig. 7.8. For norbornane, two fitting conformahons of cyclopentane in the envelope conformation can be joined in order to construct the complete 3D structure of norbornane. In this case, this is the only low-energy conformahon known for norbornane due to its rigidity. 

Fig. 7.9 Constructing ring conformations for atropine from ring templates.

Graphic module The target molecule is introduced by drawing its structure on the screen with the aid of the "mouse" and the "facilities" incorporated in the module, such as ring templates, atoms other than carbon, atomic groups, etc. which are described in the manual. All the stmctural information is stored automatically in the program as "connectivity matrices" and "tables" (one for each atom) in which the nature of the atom and other characteristics are indicated. 

Many macrocycle syntheses yield products with alkyl or aryl C-substituents, or with fused 2,6-pyridiyl, o-phenylene, or 1,2-cyclohexdiyl rings. Template-style syntheses (see Section 1.20.3) are often substituent-sensitive, and yield products with particular substituent patterns. The (3-enone/ (diamineH+) method for preparing cyclic amines (Section 1.20.2) introduces a variety of substituents on the six-membered chelate rings of cyclam, but only 3-methyl and 3,10-dimethyl substituents on the five-membered rings. Cyclams with a variety of methyl and 1,2-cyclohexdiyl substituents on the five-membered chelate rings have been prepared and structurally characterized.71... 

Figure 24 Combination of ring templates to generate conformations of a bicyclo[1.2.3]oc-tane skeleton.

P. J. DeClercq, Tetrahedron 40, 3717 (1981). [A program limited to joining ring templates]... 

Weeratunga G, Prasad GKB et al (1990) Regioselective Diels-Alder reactions of N-cyanoindoIe-4, 7-diones elaboration of the A-ring of the kinamycins on a BC ring template. Tetrahedron Lett 31 5713-5716... 

Only Zimmerman and Helson have discussed the organization, content, and construction of a ring template library. The following notes are the accumulation of experience from a pilot RTD implementation in CAMEO. ... 

Figure 53 One possible format of a ring template database. (Reprinted from Ref. 7.)...

To register, look up, or otherwise access a ring template, a canonical (i.e., unique and atom-numbering-independent) description of the RS is first obtained (Figure 54). The hash function reduces this to a short code, which acts as an address in the hash table. The hash table eventually yields the address of a ring data record where the ring is stored. 

Whether it uses stored ring templates (Zimmerman, the Chemical Abstracts Service, and Shelley do). 

Ring templates are not required. The program is rather successful with uncommon ring systems against which conventional, template-based programs would be helpless. 

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