Ring one carbon

Tamoxifen contains three aromatic (benzene) rings, one carbon-carbon double bond, one ether, and one tertiary amine. Two stereoisomers are possible, a pair of cis-trans isomers. 

Folate designates a member of the family of pteroylglutamates, each having a different level of reduction of the pteridine ring, one-carbon unit. 

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