Table 1. Tetracycline derivative structures.

Based on the simple structure of tetracycline, the naturally occurring and semi-synthetic analog structural differences are listed. Highlighted in grey is the chemical difference that exists between the effective (grey boxes) and non-effective compounds (white). The tetracycline backbone structure was made using ChemDraw (Perken Elmer informatics, Waltham, MA) and was based on information from Chopra and Roberts (Chopra and Roberts, 2001). LogD and LogP data are predicted values from ChemSpider (The Royal Society of Chemistry) (Accessed November 16, 2015) as follows: Tetracycline, ChemSpider ID=10257122, http://chemspider.com/chemical-structure.10257122.html; Oxytetracycline, ChemSpider ID=10482174, http://chemspider.com/chemical-structure.10482174.html; Chlortetracycline, ChemSpider ID=10469370, http://chemspider.com/chemical-structure.10469370.html; Doxycycline, ChemSpider ID=10469369, http://chemspider.com/chemical-structure.10469369.html; Demeclocycline, ChemSpider ID=10482117, http://chemspider.com/chemical-structure.10482117.html; Minocycline, ChemSpider ID=16735907, http://chemspider.com/chemical-structure.16735907.html; Tigecycline, ChemSpider ID=10482314, http://chemspider.com/chemical-structure.10482314.html.

Drug Name	R5	R6	R6′	R7	R9	LogD	LogP
Tetracycline	H	CH3	OH	H	H	−3.55	−1.47
Oxytetracycline	OH	CH3	OH	H	H	−4.25	−1.5
Chlortetracycline	H	CH3	OH	Cl	H	−2.43	0.33
Demeclocycline	H	H	OH	Cl	H	−3.40	−1.07
Doxycycline*	OH	CH3	H	H	H	−3.29	−0.54
Minocycline*	H	H	H	N(CH3)2	H	−2.25	0.20
Tigecycline*	H	H	H	N(CH3)2	NHCOCH2NHC(CH3)3	−2.73	−1.30

^*Semi-synthetic tetracycline