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16.1.6 Piperidines

Cyproheptadine: Cyproheptadine, 4-(dibenzo[a,d]cyclohepten-5-ylidene)-1-methylpipe-ridine (16.1.21), is synthesized by reacting 1-methyl-4-magnesiumchloropiperidine with 5H-dibeno[a,d]cycloheptene-5-one, which forms carbinol (16.1.20), the dehydration of which in an acidic medium leads to the formation of cyproheptadine (16.1.21) [39,40].

Cyproheptadine has antianaphylactic activity that is associated with its ability to slow down the release of histamine and other mediators from fat cells. It is mainly used for treating bronchial asthma attacks, allergic bronchitis, rhinitis, and allergic skin reactions as well as in adjuvant therapy for anaphylactic reactions. Synonyms of this drug are periactin and vimicon.

Terfenadine: Terfenadine, a-(4-ieri-butylphenyl) -4-hydroxydiphenylmethyl)-1-piperidinebutanol (16.1.24), is synthesized in two ways. According to the first, benzyl-4-magnesiumchloropiperidine is reacted with benzophenone, giving (1-benzyl-4-piperidyl) diphenylcarbinol (16.2.22), which undergoes further debenzylation by reduction with hydrogen using a palladium over carbon catalyst, giving (4-piperidyl)diphenylcarbinol (16.2.22). This product is alkylated by either 1-(4-ieri-butylphenyl)-4-chlorobutanol, which forms terfenadine (16.1.24), or by alkylating with (4-ieri-butylphenyl-3-chloropropiophe-none, which forms the product (16.1.25), the carbonyl group of which is reduced to an alcohol group, thus giving the desired terfenadine (16.1.24) [41-46].

MgCl O

I^^^Vr^ °H / ^ H2/Pd-C / + -" \_J C^^^N-CH2-C6H5 -»-

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