2.2.1. Inhibition of PARP-1 and PARP-2 by ADP Conjugates

The effects of 16 compounds MorXppA **4** and **10** on the autopoly(ADP-ribosyl)ation of PARP-1 and PARP-2 were studied. The inhibitory properties of NAD+ analogs are summarized in Table 1. As it can be seen from the data presented in Table 1, phosphodiester dinucleotide pyrophosphates **4** containing morpholino nucleosides conjugated to ADP through the P–O bond have a little effect on the activity of PARP-1 and PARP-2 (residual enzyme activity in the presence of 1 mM compounds is 40%–90%). Among compounds **4** an inhibition efficiency of PARP-1 increases depending on the heterocyclic base of morpholino nucleoside in the order Cyt < Ura < Ade < 5-Cl-Ura < Gua < Thy < 5-Br-Ura < 5-I-Ura. In a case of PARP-2, this order has been changed, (Cyt, Ura) < 5-Cl-Ura < Gua < (5-Br-Ura, Thy) < Ade < < 5-I-Ura for conjugates **4.** The only compound that has a significant effect on the activity of both enzymes is the 5-iodouracil derivative **4IU**.

**Table 1.** Residual PARP-1 and PARP-2 activity (%) in the presence of 1 mM compounds **4** and **10** or IC<sup>50</sup> (µ)**.**



Analogs of these compounds with the P–N bond **10** generally have a more pronounced effect on the activity of PARP-1 and PARP-2. The residual activity of the enzymes in 1 mM concentration of compounds is from 10% to 90%. The 5-iodouracil derivative **10IU** is also active, with the IC<sup>50</sup> value for PARP-1 being equal to 126 µM. Close to **10IU** in effectiveness of inhibition of both enzymes is the thymidine derivative **10T** with IC<sup>50</sup> value for PARP-1 220 µM. Activity of conjugates **10** with the P–N bond against PARP-1 changes as Ura < Cyt < Gua < 5-Br-Ura < 5-Cl-Ura < Ade < <Thy < <5-I-Ura depending on the heterocyclic base. In a case of PARP-2, this order has been changed, 5-Cl-Ura < (Cyt, Ura) < (5-Br-Ura, Gua) < Thy,5-I-Ura < <Ade for conjugates **10**.

The most active compound in the series **4** against both enzymes is the 5-I-Ura-containing analog **4IU** with IC<sup>50</sup> 255 ± 5 µM for PARP-1 and 160 ± 10 µM for PARP-2. However, compounds **10** containing a P–N bond generally have a more pronounced effect on the activity of both enzymes.

It is interesting that the most active NAD+ mimetic among the **10A,G,C,U,T,IU** series is different for PARP-1 and PARP-2 in contrast to **4** series: for PARP-1 it is compound **10IU** with IC<sup>50</sup> 126 ± 6 µM, for PARP-2 it is compound **10A** with IC<sup>50</sup> 63 ± 10 µM. The influence of the 2<sup>0</sup> -aminomethyl group of

morpholino nucleosides is more pronounced in the inhibition of PARP-2 than of PARP-1 (see adenineand thymine-containing compounds **4A** and **10A**, and **4T** and **10T**). On the other hand, compounds **4IU** and **10IU** inhibit PARP-1 almost equally independently of the P–O or P–N bond presence.
