Yoshinari Wakiyama

Synthesis of novel lincomycin derivatives and their in vitro antibacterial activities

INTRODUCTION Macrolide antibiotics are active against Gram-positive bacteria, especially Streptococcus pneumoniae, and their safety as an oral agent has already been proved. Therefore, macrolide antibiotics are regarded as very important chemotherapeutic agents against bacterial respiratory infections as in the case of b-lactam antibiotics or new quinolones. Although clarithromycin and azithromycin, which are representatives of widely used macrolides, exhibit enhanced antibacterial activities and characteristic pharmacokinetics compared with those of erythromycin, they are not active enough against resistant bacteria of S. pneumoniae with erm gene. Recently these resistant bacteria have widely spread, especially in European and Asian countries, and caused severe social problems. Chemical modifications of erythromycin provided the clinical site with two novel ketolides, telithromycin and cethromycin, which are effective against resistant bacteria of S. pneumoniae with erm gene. No oral antibiotic, however, has been launched so far, which is effective against the resistant bacteria of S. pneumoniae and does not have any problems in safety or taste. Lincomycin (LCM) isolated as a secondary metabolite from fermentation broth of Streptomyces lincolnensis was chemically transformed to a useful oral antibiotic, clindamycin (CLDM) (Figure 1), which inhibits bacterial protein synthesis in a similar manner to macrolides. Although telithromycin is still influenced by efflux pumps of resistant S. pneumoniae with mef gene, CLDM is not influenced by efflux pumps. We focused not only on its safety and effectiveness against efflux pumps but its possibility of switch therapy by CLDM analogs, and planned to generate a novel oral antibiotic, which is effective against resistant bacteria of S. pneumoniae with erm gene or mef gene by chemical modifications of LCM.

Synthesis and antibacterial activity of novel lincomycin derivatives. I. Enhancement of antibacterial activities by introduction of substituted azetidines

The synthesis and antibacterial activity of (7S)-7-sulfur-azetidin-3-yl lincomycin derivatives are described. Modification was achieved by a simple reaction of (7R)-7-O-methanesulfonyllincomycin and the corresponding substituted azetidine-2-thiol. Several compounds first showed moderate antibacterial activity against Streptococcus pneumoniae and Streptococcus pyogenes with erm gene as lincomycin derivatives.

Synthesis and structure–activity relationships of novel lincomycin derivatives. Part 2. Synthesis of 7( S )-7-deoxy-7-(4-morpholinocarbonylphenylthio)lincomycin and its 3-dimensional analysis with rRNA

Lincomycin derivatives, which possess a hetero ring at the C-7 position via sulfur atom, were synthesized by three types of reactions: (1) Mitsunobu reaction of 2,3,4-tris-O-(trimethylsiliyl)lincomycin (1) with the corresponding thiol, (2) SN2 reaction of 7-O-methanesulfonyl-2,3,4-tris-O-(trimethylsiliyl)lincomycin (2) with the corresponding thiol and (3) Pd-catalyzed cross-coupling reaction of 7-deoxy-7-epi-7-mercaptolincomycin (35) with the corresponding aryl halides. As a result, compound 28 had potent antibacterial activities against major pathogens, which caused respiratory infections, even compared with clindamycin. On the other hand, compound 38 showed most potent activities against a variety of Streptococcus pneumoniae with erm gene.

Synthesis and structure–activity relationships of novel lincomycin derivatives. Part 1. Newly generated antibacterial activities against Gram-positive bacteria with erm gene by C-7 modification

We synthesized 7(S)-7-deoxy-7-arylthiolincomycin derivatives possessing a heterocyclic ring at the C-7 position via sulfur atom by either Mitsunobu reaction of 2,3,4-tris-O-(trimethylsiliyl)lincomycin or SN2 reaction of 7-O-methanesulfonyl-2,3,4-tri-O-trimethylsiliyllincomycin. As a result, 7(S)-7-deoxy-7-arylthiolincomycin derivatives 16, 21 and 27 exhibited antibacterial activities against respiratory infection-related Gram-positive bacteria with erm gene, although clindamycin did not have any activities against those pathogens. Furthermore, 7(S)-configuration of lincomycin derivatives was found to be necessary for enhancing antibacterial activities from the comparison results of configurations of 16 (S-configuration) and 30 (R-configuration) at the 7-position.

Synthesis and antibacterial activity of novel lincomycin derivatives. II. Exploring (7S)-7-(5-aryl-1,3,4-thiadiazol-2-yl-thio)-7-deoxylincomycin derivatives

The synthesis and antibacterial activity of (7S)-7-(5-aryl-1,3,4-thiadiazol-2-yl-thio)-7-deoxylincomycin derivatives are described. These derivatives were mainly prepared by the Mitsunobu reaction of 2,3,4-tris-O-(trimethylsilyl)lincomycin and the corresponding thiols. Exploring structure–activity relationships of the substituent at the 5 position of a thiadiazole ring revealed that compounds with the ortho substituted phenyl group showed improved antibacterial activities against Streptococcus pneumoniae and Streptococcus pyogenes with erm gene compared with the reported compound (1) that had an unsubstituted benzene ring.

Synthesis and structure-activity relationships of novel lincomycin derivatives part 3: discovery of the 4-(pyrimidin-5-yl)phenyl group in synthesis of 7(S)-thiolincomycin analogs.

Novel lincomycin derivatives possessing an aryl phenyl group or a heteroaryl phenyl group at the C-7 position via sulfur atom were synthesized by Pd-catalyzed cross-coupling reactions of 7(S)-7-deoxy-7-thiolincomycin (5) with various aryl halides. This reaction is the most useful method to synthesize a variety of 7(S)-7-deoxy-7-thiolincomycin derivatives. On the basis of analysis of structure–activity relationships of these novel lincomycin derivatives, we found that (a) the location of basicity in the C-7 side chain was an important factor to enhance antibacterial activities, and (b) compounds 22, 36, 42, 43 and 44 had potent antibacterial activities against a variety of Streptococcus pneumoniae with erm gene, which cause severe respiratory infections, even compared with our C-7-modified lincomycin analogs (1–4) reported previously. Furthermore, 7(S)-configuration was found to be necessary for enhancing antibacterial activities from comparison of configurations at the 7-position of 36 (S-configuration) and 41 (R-configuration).

Synthesis and antibacterial activity of novel lincomycin derivatives. III. Optimization of a phenyl thiadiazole moiety

Lincomycin derivatives that have a 5-(2-nitrophenyl)-1,3,4-thiadiazol-2-yl thio moiety at the 7-position were synthesized. 5-Substituted 2-nitrophenyl derivatives showed potent antibacterial activities against Streptococcus pneumoniae and Streptococcus pyogenes with erm gene. Antibacterial activities of the 4,5-di-substituted 2-nitrophenyl derivatives were generally comparable to those of telithromycin (TEL) against S. pneumoniae with erm gene and clearly superior to those of TEL against S. pyogenes with erm gene. Compounds 6 and 10c that have a methoxy group at the 5-position of the benzene ring exhibited activities comparable to TEL against Haemophilus influenzae. These results suggest that lincomycin derivatives modified at the 7-position would be promising compounds as a clinical candidate. We would like to dedicate this article to the special issue for late Professor Dr. Hamao Umezawa in The Journal of Antibiotics.

Synthesis and structure–activity relationships of novel lincomycin derivatives. Part 4: synthesis of novel lincomycin analogs modified at the 6- and 7-positions and their potent antibacterial activities

To modify lincomycin (LCM) at the C-6 and the C-7 positions, we firstly prepared various substituted proline intermediates (7, 11–15 and 17). These proline intermediates were coupled with methyl 1-thio-α-lincosamide and tetrakis-O-trimethylsilylation followed by selective deprotection of the TMS group at the 7-position gave a wide variety of key intermediates (23–27, 47 and 50). Then, we synthesized a variety of novel LCM analogs modified at the 7-position in application of the Mitsunobu reaction, an SN2 reaction, and a Pd-catalyzed cross-coupling reaction. Compounds 34 and 35 (1′-NH derivatives) exhibited enhanced antibacterial activities against resistant pathogens with erm gene compared with the corresponding 1′-N-methyl derivatives (3 and 37). On the basis of reported SAR, we modified the 4′-position of LCM derivatives possessing a 5-(2-nitrophenyl)-1,3,4-thiadiazol-2-yl group at the C-7 position. Compound 56 showed significantly potent antibacterial activities against S. pneumoniae and S. pyogenes with erm gene, and its activities against S. pneumoniae with erm gene were improved compared with those of 34 and 57. Although we synthesized novel analogs by transformation of a C-7 substituent focusing on the 1′-demethyl framework to prepare very potent analogs 73 and 75, it was impossible to generate novel derivatives exhibiting stronger antibacterial activities against S. pneumoniae with erm gene compared with 56.

Synthesis and SARs of novel lincomycin derivatives Part 5: optimization of lincomycin analogs exhibiting potent antibacterial activities by chemical modification at the 6- and 7-positions

In order to modify lincomycin at the C-6 and C-7 positions, we prepared target molecules, which have substituted pipecolinic acid at the 6-amino group and a para-substituted phenylthio group at the C-7 position, in application of palladium-catalyzed cross-coupling as a key reaction. As the result of structure-activity relationship (SAR) studies at the 6-position, analogs possessing 4′-cis-(cyclopropylmethyl)piperidine showed significantly strong antibacterial activities against Streptococcus pneumoniae and Streptococcus pyogenes with an erm gene. On the basis of SAR, we further synthesized novel analogs possessing 4′-cis-(cyclopropylmethyl)piperidine by transformation of a C-7 substituent. Consequently, novel derivatives possessing a para-heteroaromatic-phenylthio group at the C-7 position exhibited significantly strong activities against S. pneumoniae and S. pyogenes with an erm gene even when compared with those of telithromycin. Finally, in vivo efficacy of selected two derivatives was evaluated in a rat pulmonary infection model with resistant S. pneumoniae with erm + mef genes. One of them exhibited strong and constant in vivo efficacy in this model, and both compounds showed strong in vivo efficacy against resistant S. pneumoniae with a mef gene.

Synthesis and antibacterial activity of novel lincomycin derivatives. IV. Optimization of an N -6 substituent

The design and synthesis of lincomycin derivatives modified at the C-6 and C-7 positions are described. A substituent at the C-7 position is a 5-aryl-1,3,4-thiadiazol-2-yl-thio group that generates antibacterial activities against macrolide-resistant Streptococcus pneumoniae and Streptococcus pyogenes carrying an erm gene. An additional modification at the C-6 position was explored in application of information regarding pirlimycin and other related compounds. These dual modifications were accomplished by using methyl α-thiolincosaminide as a starting material. As a result of these dual modifications, the antibacterial activities were improved compared with those of compounds with a single modification at the C-7 position. The antibacterial activities of selected compounds in this report against macrolide-resistant S. pneumoniae and S. pyogenes with an erm gene were superior to those of telithromycin.