206 F. L. HORSFALL, JR. 



1.3 mg. per milliliter completely suppressed virus increase when the compound 

 was added at 1 or 2 hours, was considerably less effective when added at 3 or 4 

 hours, and had no effect on reproduction at 6 hours after inoculation. The 

 latent period of influenza A virus in the chorioallantoic membrane in vitro is 

 about 3 hours (Ackermann and Maassab, 1954a,b). The compound is most 

 effective during the first two-thirds of the latent period but has some 

 inhibitory effect during the last third of the latent period and a slight but 

 definite activity even later in the cycle. 



The inhibitory effect of the compound is blocked by L-methionine but not 

 by D-methionine (Ackermann, 1951a). This result was taken to indicate that 

 L-methionine is involved in the biosynthesis of influenza A virus and it was 

 suggested that some function of methionine rather than its synthesis is 

 inhibited by the analog (Ackermann, 1951a). 



DL-Methoxinine does not inactivate the infectivity of the virus in vitro, 

 does not prevent attachment to or penetration of host cells, and does not 

 affect the endogenous respiration of the chorioallantoic membrane (Acker- 

 mann, 1951a). Moreover, the compound does not irreversibly impair the 

 capacity of the tissue to support virus multiplication; on removal and 

 addition of methionine, multiplication proceeds as in control membranes 

 (Ackermann, 1951a). The results obtained with DL-methoxinine support the 

 view that some phase-specific reactions exist and that one of these involves 

 methionine. The function of this reaction appears to be completed before 

 the appearance of the infectious property of the virus (Ackermann and 

 Maassab, 1954b). 



Methoxinine also inhibits the multiplication of vaccinia virus in chick 

 embryo tissue in vitro (Thompson, 1947). The relation of the inhibitory effect 

 to steps in the cycle of vaccinia virus multiplication is not known. 



4. 5, 6-Dichloro-l-(3-D-ribofuranosylbenzimidazole (DRB) 



a. Inhibition of Influenza Virus Multiplication. This compound, designated 

 DRB, was synthesized during a systematic investigation of the inhibitory 

 activity of glycosides of benzimidazoles in relation to their chemical structure 

 (Tamm et al., 1954). It inhibits the multiplication of influenza B virus in the 

 chorioallantoic membrane of the chick embryo in vitro (Tamm et al., 1954). 



In single-cycle multiplication experiments (Tamm and Tyrrell, 1954), the 

 compound at 0.018 mg. per milliliter inhibited reproduction markedly when 

 added at 1 or 2 hours but had little or no effect at 3 hours after inoculation. 

 It also inhibited the production of soluble complement-fixing antigen, though 

 less markedly than that of virus particles, when added at 0.5 hours, but not at 

 1 hour. Both as regards virus multiplication and production of soluble 

 antigen, the later the compound was added during the latent period the 

 smaller was the degree of inhibition. The latent period of influenza B virus in 



