**3. Concluding remarks**

In summary, the coupling of a arylsulfonyl and benzenesulfonamido moiety to the 9a position of 15-membered azalide scaffold *via* carbamoyl linker has indicated improvement in antibacterial activity of novel azalides.

Antibacterial activity increased

Fig. 5. Antibacterial activities of urea and thiourea derivatives of 15-membered azalides in comparison to sulfonylurea analogues.

ribosome. In spite of the knowledge gained so far on macrolide binding, (Novak et al., 2006; Novak et al., 2009; Auerbach et al., 2009; Schlunzen et al., 2003; Hansen et al., 2002; Berisio et al., 2003) an understanding of the mode of their interactions with ribosome still remain incomplete with many issues unresolved. Therefore, it can only be speculated about the possible binding mode of the compound **35a** but it is likely that the additional interaction involving 1-naphthyl-propyl- side-chain, attached at the 9a position, might lead to a further

In summary, the coupling of a arylsulfonyl and benzenesulfonamido moiety to the 9a position of 15-membered azalide scaffold *via* carbamoyl linker has indicated improvement

> O O

> > O OH

O O

> O OH

O

N

O

HO OH

O

O O

> O OH

O O

> O OH

O

N

O

HO OH

CN

O

N

R'

O

HO OH

CN

O O

> O O

HO

N

OH

**13 X=O 14 X=S**

N N H X

R'''

HO

N

OH

N N H O

SO2

N

R'

O

Antibacterial activity increased

HO OH

O O

**3 5 7**

O O

HO

N

OH

**11 X=O 12 X=S**

NH N H X

R'''

HO

N

OH

NH N H O

SO2

Fig. 5. Antibacterial activities of urea and thiourea derivatives of 15-membered azalides in

Antibacterial activity increased

stabilization of a complex with ribosome (Bukvić Krajačić et al., 2011a).

**3. Concluding remarks** 

O O

> O OH

O O

> O OH

O

N

O

O

N

R'

O

OH HO OH

O O

> N H X

R'

N

HO HO OH

OH

O O

> **8 X=O 9 X=S**

HO

O

N

N H SO2

in antibacterial activity of novel azalides.

comparison to sulfonylurea analogues.

Hence, newly synthesised sulfonyl ureas of azalides **3b**-**3f**, and azalide-sulfonamide conjugates **10a** and **10b** displayed significantly improved activity against inducible resistant *S. pyogenes* strain when compared to azithromycin.

In addition, the introduction of carbamoyl and thiocarbamoyl group at the 9a position of azithromycin like azalide skeleton *via* propyl linker proved to be promising method to tackle the resistance problems.

As a result of a preliminary optimization of an alkyl/aryl moiety attached at the carbamoyl and thiocarbamoyl group all prepared and tested compounds had high *in vitro* activity against erythromycin susceptible Gram-positive aerobes and Gram-negative microorganisms and especially resistant *S. pyogenes* and *S. pneumoniae strains.* It was also, shown here that urea and thiourea derivatives of 3-decladinosyl-3-hydroxy azalides, although lacking a cladinose sugar, showed noticeable antibacterial activity.

Overall mutual comparison of obtained results can be summarized in three items:

• The observed increase of antibacterial activity in the series of ureas and thioureas **11, 12, 13** and **14** (Bukvić Krajačić et al., 2009) in comparison with those of their analogues **8** and **9**  (Kujundžić et al., 1995), was opposite to the results obtained for the sulfonylcarbamoyl derivatives **3, 5** and **7** (Bukvić Krajačić et al., 2005) where a decrease of activity was found when sulfonylcarbamoyl moiety was further away from the azalide ring (Fig. 6)

Fig. 6. Antibacterial activity of selected novel sulfonylureas, ureas and thioureas of 15 membered azalides on *S. Pneumoniae efflux-mediated* (Bukvić Krajačić et al., 2009) and *S. pyogenes* iMLS (Bukvić Krajačić et al., 2005) resistant strains in comparison to azithromycin

• Several novel sulfonylureas (Bukvić Krajačić et al., 2005), ureas and thioureas (Bukvić Krajačić et al. 2009) of 15-membered azalides showed same or significantly better activity

Antibacterial Activity of Novel Sulfonylureas, Ureas and Thioureas of 15-Membered Azalides 101

In general, novel sulfonylureas, ureas and thioureas of 15-membered azalides and their 3 decladinosyl-3-hydroxy derivatives showed their potential to serve as a good platform for further investigation in order to discover new derivatives having an improved overall

The Ministry of Science, Education and Sports of the Republic of Croatia is acknowledged

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Alihodžić, S.; Fajdetić, A.; Kobrehel, G.; Lazarevski, G.; Mutak, S.; Pavlović, D.; Štimac, V.;

Allen, N., (1977). Macrolide Resistance in *Staphylococcus aureus*: Inducers of Macrolide

Andersen, S. L.; Ager, A. L.; McGreevy, P.; Schuster, B. G.; Ellis, W.; Berman, J. (1994).

Andersen, S. L.; Ager, A.; McGreevy, P.; Schuster, B. G.; Wesche, D.; Kuschner, R.; Ohrt, C.;

Anonymous (2000) Heroes of Chemistry Recipients, American Chemical Society Portal, http://portal.acs.org/portal/acs/corg/content?\_nfpb=true&\_pageLabel=PP\_SUP ERARTICLE&node\_id=1464&use\_sec=false&sec\_url\_var=region1&\_\_uuid=91e8ce

Auerbach, T.; Mermershtain, I.; Bashan, A.; Davidovich, C.; Rozenberg, H.; Sherman, D. H.;

Yonath, A. (2009). Structural basis for the antibacterial activity of the 12-memberedring mono-sugar macrolide methymycin *Biotechnologia,* Vol.1, (January 2009), pp.

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Dussarat, A.; Fromentin, C.; D'Ambrieres, S. G.; Lachaud, S.; Laurin, P.; Martret, O. L.; Loyau, V. & Tessot, N. (1998). Synthesis and Antibacterial Activity of Ketolides (6-*O*-Methyl-3-oxoerythromycin Derivatives): A New Class of Antibacterials Highly Potent Against Macrolide-Resistant and -Susceptible Respiratory Pathogens. *Journal of Medicinal Chemistry*, Vol. 41, No. 21, (September 1998) pp.

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biological profile with a special emphasis on resistant bacterial strains.

for the financial support (Project No. 006-0000000-3216).

4080-4100, ISSN 0022-2623

769, ISSN 0021-8820

24-35, ISSN 0860-7796

ISSN 1098-6596.

1098-6596

**4. Acknowledgements** 

**5. References** 

on *S. pneumoniae efflux-mediated and S. pyogenes* iMLS resistant strains in comparison to azithromycin (Fig 7). Among them, new ureas with naphtyl substituents (**11f, 11g** & **11h**) showed better activity against inducible resistant *S. pyogenes* in comparison to azithromycin. Ureas **11f** & **11g** and thioureas **12c, 12d, 12e** and **12f** possess good activity against efflux-mediated resistant *S. pyogenes*, comparable to azithromycin.

Fig. 7. Antibacterial activity of 3-decladinosyl-3-hydroxy ureas and thioureas on *S. pneumoniae* efflux-mediated resistant strain (Bukvić Krajačić et al., 2011) in comparison to their parent 3-cladinosyl analogues (Bukvić Krajačić et al., 2009) and test standards azithromycin (**1**) and 3-decladinosyl azithromycin (**16**).

• Contrary to the well known fact (LeMahieu, et.al., 1974; Kaneko et.al., 2006; Pal, 2006; Tanikawa, et.al., 2001; Mutak, 2007) and previous results (Bukvić Krajačić et al., 2005, Bukvić Krajačić et al., 2007; Marušić Ištuk et al., 2007), that simple removal of cladinose sugar from macrolides significantly decreases antibacterial activity, unexpectedly, some of the newly discovered 3-decladinosyl-3-hydroxy ureas **33** & **34**, and thioureas **35** & **36** (Bukvić Krajačić et al., 2011) maintain good antibacterial activity against panel of key respiratory Gram-positive and Gram-negative pathogens. Against efflux-mediated resistant *S. pneumoniae* strain they posses comparable or better activity (MIC 2 -16 µg/ml) to their 3-cladinosyl parent analogues **11** & **13** (MIC 4 -16 µg/ml) (Bukvić Krajačić et al., 2009) and azithromycin (**1**) (MIC 8 µg/ml), and significantly better in comparison to the inactive 3-decladinosyl azithromycin (**16**) (MIC >64 µg/ml) (Fig. 7) (Bukvić Krajačić et al., 2011). Also, some 3-decladinosyl-3-hydroxy ureas **33** & **34**, and thioureas **35** & **36**, maintain antibacterial activity against Gram-negative pathogens *H. influenzae* and *M. catarrhalis* in comparison to their parent 3-cladinosyl derivatives (Bukvić Krajačić et al., 2009), and comparable to azithromycin, but demonstrate a large improvement in comparison with inactive 3-decladinosyl azithromycin **16** (Bukvić Krajačić et al., 2011) and other 3-decladinosyl derivatives reported in literature. These small library of 3-decladinosyl-3-hydroxy ureas and thioureas of 15-membered azalides we termed *"decladinosylides."*

In general, novel sulfonylureas, ureas and thioureas of 15-membered azalides and their 3 decladinosyl-3-hydroxy derivatives showed their potential to serve as a good platform for further investigation in order to discover new derivatives having an improved overall biological profile with a special emphasis on resistant bacterial strains.
