Cyclopentane rings

Cyclopentene derivatives with carboxylic acid side-chains can be stereoselectively hydroxy-lated by the iodolactonization procedure (E.J. Corey, 1969, 1970). To the trisubstituted cyclopentene described on p. 210 a large iodine cation is added stereoselectively to the less hindered -side of the 9,10 double bond. Lactone formation occurs on the intermediate iod-onium ion specifically at C-9ot. Later the iodine is reductively removed with tri-n-butyltin hydride. The cyclopentane ring now bears all oxygen and carbon substituents in the right stereochemistry, and the carbon chains can be built starting from the C-8 and C-12 substit""" ... 

I eplanocins. Neplanocins A—D and E (37—41) are carbocycHc nucleoside antibiotic products oi Ampullariella regularis (1,4) that are stmcturaHy related to (36) in that they contain either a cyclopentene or epoxy cyclopentane ring (121,122). The chemical syntheses of (37—41) and the 3-deazaneplanocins have been reported (123—126). Compound (37), which is converted to its 5 -triphosphate, has potent antitumor and antiviral activities (127—129). It strongly inhibits SAM in ceUs and vimses (128—131) and is converted to the 3 -keto derivative by A-adenosyUiomocysteine hydrolase (132,133). 

Oxeladin [468-61-1] (54), an antitussive developed in the UK, is stmcturaHy related to carbetapentane in that the cyclopentane ring has been broken at the 3,4-bond. It is also similar pharmacologically. Extensive clinical studies using cough drops and symp containing oxeladin are described (73). The compound can be synthesized from phenylacetonitrile (74). 

In addition to unsaturated fatty acids, several other modified fatty acids are found in nature. Microorganisms, for example, often contain branched-chain fatty acids, such as tuberculostearic acid (Figure 8.2). When these fatty acids are incorporated in membranes, the methyl group constitutes a local structural perturbation in a manner similar to the double bonds in unsaturated fatty acids (see Chapter 9). Some bacteria also synthesize fatty acids containing cyclic structures such as cyclopropane, cyclopropene, and even cyclopentane rings. 

Content and composition of essential oils from Nepeta L. species, most of them containing diastereomeric nepetalactones, unsaturated 8-lactones with annelated cyclopentane ring 98KPS84. 

This past decade, however, has seen the elucidation of a po-Ient class of biologically active compounds that have in common. 1 cyclopentane ring. It is to these, the prostaglandins, that we oddress ourselves first. 

Prostaglandin F, a hormone that causes uterine contraction during childbirth, has the following structure. Are the two hydroxyl groups (-OH) on the cyclopentane ring cis or trans to each other What about the two carbon chains attached to the ring ... 

PGF2a- The cyclopentane ring of the Corey lactone (9) is the host of four contiguous stereogenic centers. Retrosynthetic simplification of 9 provides 10, a construct which is more complex than 9 Nevertheless, intermediate 10 possesses structural features that satisfy the requirement for the iodolactonization transform. The iodolactone in 10 constitutes the retron for the iodolactonization transform.11 Cleavage of the indicated bonds in 10 sacrifices two of the five stereocenters and provides unsaturated carboxylic acid... 

Construction of the cyclopentane ring was accomplished by utilization of Trosf s Pd-mediated diastereoselective [3+2] trimethylenemethane (TMM) cycloaddition [4] on the cinnamate 5 having an Evans type chiral auxiliary [4b], The resulting diastereomeric mixture (3 1 at best) of 7a and 7b was separated by careful silica gel column chromatography (7a is less polar than 7b under normal phase). Puri-... 

The vinylcyclopropane 144, bearing two electron-withdrawing groups, undergoes the intermolecular palladium-catalyzed [3 + 2]cycloaddition reaction of the Jt-allylpalladium intermediate 145 with a,/ -unsaturated esters or ketones to provide a useful method for forming the cyclopentane ring of 146 [74], (Scheme 51)... 

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