Structure-activity relationships among substituted N-benzoyl derivatives of phenylalanine and its analogues in a microbial antitumor prescreen III: derivatives of p-fluoro-DL-phenylalanine.

Twelve substituted benzoyl derivatives of p-fluoro-DL-phenylalanine were prepared and tested for growth-inhibitory activity in a Lactobacillus casei system used as an antitumor prescreen. The 12 substituted benzoyl groups were the same as those attached to o-fluorophenylalanine and m-fluorophenylalanine studied earlier. The activity of these compounds was compared vertically among themselves and horizontally with the corresponding derivatives of o-fluorophenylalanine and of m-fluorophenylalanine. It was found that the derivatives of p-fluorophenylalanine, like those of o- and m-fluorophenylalanine, exhibited remarkable inhibition, all but one, i.e., the o-nitrobenzoyl derivative, showing inhibition that is considered to be positive in the prescreen. Particularly potent compounds in this group were the m-chlorobenzoyl-, p-chlorobenzoyl, m-nitrobenzoyl, and p-nitrobenzoyl derivatives. Comparison of the activity of the substituted benzoyl derivatives of all three structural isomers of fluorophenylalanine at equimolar concentrations showed that the derivatives of m-fluorophenylalanine were generally better inhibitors than those of o-fluoro- or p-fluorophenylalanine. Study of the ID50 values of the more active substituted benzoyl derivatives of the fluorophenylalanines showed that the most active of this group was m-chlorobenzoyl-p-fluoro-DL-phenylalanine.

Use of a Lactobacillus casei assay as a prescreen for potential anticancer agents: an update study.

Updating an earlier report, 15 known antineoplastic agents, 11 of which are commercially available for treatment of human cancers, were tested for growth-inhibitory activity in a Lactobacillus casei system to determine if this microbial system could select them as "active." Although we previously reported that over 160 compounds tested in this assay were inactive, 11 of the 15 known antineoplastic agents tested here were inhibitory. Because of this observation and the advantage that the procedure is rapid and inexpensive, this microbiological assay is recommended for consideration as a prescreen for anticancer agents.

The study of structure-activity relationships among substituted N-benzoyl derivatives of phenylalanine and its analogs in a microbial antitumor prescreen: II. Derivatives of m-fluoro-DL-phenylalanine.

The fluoro-, chloro-, methoxy- and nitro-substituted benzoyl derivatives of m-fluoro-DL-phenylalanine, substituted singly at the ortho, meta or para position of the benzoyl phenyl ring, were prepared and tested for growth-inhibitory activity in a Lactobacillus casei system used as an antitumor prescreen. The substituted benzoyl derivatives that were previously found to be the most active for o-fluoro-DL-phenylalanine were also the most active for the m-fluoro-DL-phenylalanine. The position of the fluorine substituent in the phenylalanine also appeared to be important for inhibitory activity as the derivatives of m-fluoro-phenylalanine were in general better inhibitors than those of the corresponding o-fluorophenylalanine.

m- And p-halobenzoyl derivatives of p-halo-DL-phenylalanine as inhibitors in a microbial antitumor prescreen.

Meta- and p-halobenzoyl-p-halo-phenylalanine compounds were prepared and tested for growth-inhibitory activity in a Lactobacillus casei system. The activity of 13 of the most active of these compounds, reported here, was greater than that of any other acyl derivatives of amino acid analogs previously studied in this system and was from 2 to 8 times greater than that of 6-mercaptopurine, a known antitumor agent.

Structure-activity relationships among substituted N-benzoyl derivatives of phenylalanine and its analogs in a microbial antitumor prescreen I: Derivatives of o-fluoro-DL-phenylalanine.

Twelve derivatives of 0-fluoro-dl-phenylalanine containing fluorine, chlorine, methoxy, and nitro radicals in various positions of the aromatic ring of the benzoyl group were prepared and tested in a Lactobacillus casei system. It was found that most substitutions in the benzoyl phenyl ring resulted in a compound exhibiting greater growth-inhibiting activity than the nonsubstituted benzoyl-o-fluorophenylalanine. The greatest activity was observed in the ortho-substituted fluoro compound and the meta- and para-substituted chloro and nitro compounds. With the methoxy group, the position of substitution appeared unimportant, since all three methoxy isomers exhibited essentially equal inhibition. Nitro substitution in the ortho position had a protective effect in that the product was less active than the unsubstituted benzoyl-o-fluoro-dl-phenylalanine.

Effect of chloroacetyl derivatives of para-substituted phenylalanines on microbial antitumor prescreens.

The chloroacetyl derivatives of four representative para-substituted phenylalanines, N-chloroacetyl-p-chloro-DL-phenylalanine, N-chloroacetyl-p-nitro-DL-phenylalanine, Na,Np-di(chloroacetyl)-p-amino-DL-phenylalanine, and N-chloroacetyl-O-methyl-methyl-L-tyrosine, were prepared and tested for growth inhibitory activity in Lactobacillus casei. The inhibition with these compounds approximated that of most other inhibitory chloroacetyl amino acids reported previously. However, N-chloroacetyl-p-chloro-DL-phenylalanine, the most active of these compounds, exhibited an activity approximately that of N-chloroacetyl-beta-hydroxy-D-norleucine B, the most active N-chloroacetyl derivative studied thus far. In view of this finding, the N-chloroacetyl derivatives of other para-halogenated phenylalanines were prepared and tested. The inhibitory capacity of the N-chloroacetyl derivatives of p-bromo- and p-iodophenylalanine was even greater than that of p-chlorophenylalanine, and the order of activity of these compounds increased from the chloroacetyl derivative of p-chloro- to that of p-bromo- to that of p-iodo-DL-phenylalanine. The activity of N-chloroacetyl-p-bromo- and N-chloroacetyl-p-iodo-DL-phenylalanine was a great as that of the ring-substituted N-benzoylphenylalanines, the most potent N-acyl derivatives observed.

N-Benzoyl derivatives of amino acids and amino acid analogs as growth inhibitors in microbial antitumor screen.

Twenty-seven N-benzoyl derivatives of amino acids and amino acid analogs were prepared and tested for growth-inhibitory activity in a microbial antitumor screen. Of these, 19 showed some inhibitory capacity, from a modest 13% to a potent 96% at 1 mg/ml. The activities of the "modest" inhibitors were comparable to those of most inhibitory chloracetyl and trifluoroacetyl derivatives reported earlier. The intermediate inhibitors were as active as N-chloroacetyl-beta-hydroxy-D-norleucine isomer B, the most active acyl derivative noted previously. The most active compounds in this study were N-benzoyl-p-chloro-DL-phenylalanine and N-benzoyl-m-fluoro-DL-phenylalanine, which inhibited the test organism almost completely under the assay conditions.

Effect of N-trifluoroacetyl derivatives of amino acids and amino acid analogs on microbial antitumor screen.

Eighteen trifluoroacetyl derivatives of amino acids and of amino acid analogs were prepared and tested for growth-inhibitory activity using a Lactobacillus casei system as a prescreen for antitumor activity. Of the compounds tested, the trifluoroacetyl derivatives of o-, m-, and p-fluorophenylalanine and of beta-3-thienylalanine showed modest activity; trifluoroacetyl derivatives of phenylalanine and of beta-2-thienylalanine showed marginal activity. The activity exhibited by the active trifluoroacetyl compounds was equal to that noted for most active chloroacetyl derivatives reported previously, as judged by comparison of their activity with that of chloroacetyl-m-fluorophenylalanine. No reversal of inhibition was noted when a representative of these inhibitors was challenged with a corresponding natural metabolite, both as a free amino acid and as a noninhibitory acylated compound.

Effect of acylated amino acids and acylated amino acid analogs on microbial antitumor screen.

A series of N-acetyl,-N-propionyl, and N-chloroacetyl derivatives of amino acids and amino acid analogs was tested for growth-inhibitory activity using a Lactobacillus casei system as a prescreen for possible antitumor activity. While none of the acetyl or propionyl derivatives of these amino acids and amino acid analogs caused any remarkable inhibition, certain chloroacetyl derivatives exhibited significant activity. The chloroacetyl derivatives, especially those of essential amino acids and of analogs of essential amino acids, showed modest, but pharmacologically significant, inhibition; those of nonessential amino acids exhibited no activity. When two such inhibitory acyl derivatives were combined in a single assay, the extent of inhibition was neither additive nor synergistic but was that of the more active of the two test components.