A pinboard by
Carolyn Ladd

I am a PhD candidate in Organic Chemistry who is passionate about drug design and development.


Discover how boron-incorporation is transforming drug design and related therapeutic uses.

Substituting boron for carbon within drug candidates is emerging as a promising strategy towards discovering an entirely new generation of drugs able to distinctly interact with the desired targets compared to carbon. Additionally, carboranes are attracting interest as pharmacophores. Aside from drug design, boron-derivatives and carboranes exhibit applications towards boron neutron capture therapy (BNCT), a promising alternative to conventional radiotherapy. The underexplored potential of boron is only starting to be exploited and will continue to change the face of drug design and therapeutics.


Synthesis and antiproliferative and antiviral activity of carbohydrate-modified pyrrolo[2,3-d]pyridazin-7-one nucleosides.

Abstract: Sugar-modified analogs of 4-amino-1-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyridazin-7-one (1) and 4-amino-3-bromo-1-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyridazin-7- one (3) were prepared in an effort to obtain selective antiviral agents. Treatment of ethyl 3-cyano-1-(2,3,5-tri-O-benzyl-1-beta-D-arabinofuranosyl)pyrrole-2- carboxylate (6) with hydrazine afforded 4-amino-1-(2,3,5-tri-O-benzyl-1-beta-D- arabinofuranosyl)pyrrolo[2,3-d]pyridazin-7-one (7). Treatment of 7 with bromine afforded 4-amino-3-bromo-1-(2,3,5-tri-O-benzyl-beta-D-arabinofuranosyl) pyrrolo[2,3-d]pyridazin-7-one hydrobromide (9). The benzyl ether functions of 7 and 9 were removed with boron trichloride to afford 4-amino-1-(beta-D-arabinofuranosyl)pyrrolo[2,3-d]pyridazin-7-one (8) and its 3-bromo analog 10. 4-Amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)pyrrolo[2,3-d]pyrida zin-7- one (13) was prepared by the sodium salt condensation of ethyl 3-cyanopyrrole-2-carboxylate (5) with 2-deoxy-3,5-di-O-p-toluoyl-alpha-D-erythro-pentofuranosyl chloride (11) followed by ring annulation with hydrazine. Deprotection of ethyl 3-cyano-1-(2-deoxy-3,5-di-O-p-toluoyl-beta-D-erythro-pentofuranosyl)pyrr ole- 2-carboxylate (12) using sodium ethoxide furnished ethyl 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-3-cyanopyrrole-2-carboxy late (14) which served as the starting material for the preparation of 4-amino-1-(2,3-dideoxy-beta-D-glycero-pentofuranosyl)pyrrolo[2,3-d] pyridazin-7-one (20). Selective protection of the 5'-hydroxyl group of 14 with tert-butyldimethylsilyl chloride followed by a Barton type deoxygenation sequence of the 3'-hydroxyl groups afforded ethyl 3-cyano-1-[2,3-dideoxy-5-O-tert-butyldimethylsilyl)-beta-D-glycero- pentofuranosyl]pyrrole-2-carboxylate (18). Deprotection of 18 with tetra-n-butylammonium fluoride and ring annulation with hydrazine afforded 20. The acyclic analog 4-amino-1-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3-d]pyridazin -7-one (24) was prepared via the sodium salt glycosylation of 5 with (1,3-dihydroxy-2-propoxy)methyl bromide (22) followed by a ring annulation with hydrazine. N-Bromosuccinimide treatment of 13, 20, and 25 afforded the 3-bromo derivatives 15, 21, and 25. Evaluation of these compounds in L1210, HFF, and KB cells showed that the sugar-modified analogs all were less cytotoxic than their corresponding ribonucleoside analogs. The compounds also were less active against human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1). The 3-bromo derivatives were much more active than the 3-unsubstituted analogs in both the cytotoxicity, and antiviral assays. However, there was only modest separation between activity against HCMV and cytotoxicity and there was virtually no selectivity for activity against HSV-1.

Pub.: 28 Feb '97, Pinned: 11 Apr '17

Synthesis of ethyleneoxide modified 3-carboranyl thymidine analogues and evaluation of their biochemical, physicochemical, and structural properties.

Abstract: Eleven 3-carboranyl thymidine analogues (3CTAs) containing highly hydrophilic and flexible ethyleneoxide moieties were synthesized as potential agents for boron neutron capture therapy (BNCT) and their biochemical and physicochemical properties were evaluated. Based on specific structural features, this library of 3CTAs was divided into three subgroups. The first group contained 3CTAs with 1-4 ethyleneoxide units between the thymidine (Thd) scaffold and a carborane cluster. The second group of 3CTAs contained a pentylene spacer between Thd and the carborane and 2-4 ethyleneoxide units additionally attached to the carborane cluster. The third group contained three 3CTAs all with pentylene spacers and four ethylene units but with different carborane cages. The ethyleneoxide modified 3CTAs were good substrates of thymidine kinase 1 (TK1) and poor substrates of human mitochondrial thymidine kinase 2 (TK2) as determined in phosphoryl transfer assays. In the first group of 3CTAs, all the compounds were efficiently phosphorylated regardless of varying spacer lengths (37-42% of the activity of Thd). The second group of 3CTAs was less effectively phosphorylated (17-26% of the activity of Thd) probably due to a less favorable sterical orientation of Thd within the active site of TK1 and/or an increased lipophilicity compared with the first group. In the third group of structural isomers, no significant differences in phosphorylation rates were observed (17-25%). A structure-function hypothesis explaining these results is presented.

Pub.: 01 Sep '04, Pinned: 11 Apr '17

Carbonic anhydrase inhibitors. Synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, and IX with boron-containing sulfonamides, sulfamides, and sulfamates: toward agents for boron neutron capture therapy of hypoxic tumors.

Abstract: A library of boron-containing carbonic anhydrase (CA, EC inhibitors, including sulfonamides, sulfamides, and sulfamates is reported. The new compounds have been synthesized by derivatization reactions of 4-carboxy-/amino-/hydroxy-phenylboronic acid pinacol esters with amino/isothiocyanato-substituted aromatic/heteroaromatic sulfonamides or by sulfamoylation reactions with sulfamoyl chloride. The new derivatives have been assayed for the inhibition of three physiologically relevant CA isozymes, the cytosolic CA I and II, and the transmembrane, tumor-associated isozyme CA IX. Effective inhibitors were detected both among sulfonamides, sulfamates, and sulfamides. Against the human isozyme hCA I the new compounds showed inhibition constants in the range of 34-94nM, against hCA II in the range of 3.1-48nM, and against hCA IX in the range of 7.3-89nM, respectively. As hypoxic tumors highly overexpress CA IX, the design of boron-containing inhibitors with high affinity for the tumor-associated CA isozymes may lead to important advances in boron neutron capture therapy (BNCT) applications targeting such tumors, which are non-responsive to both classical chemo- and radiotherapy.

Pub.: 24 May '05, Pinned: 11 Apr '17

Promising carboranylquinazolines for boron neutron capture therapy: synthesis, characterization, and in vitro toxicity evaluation.

Abstract: Novel classes of structurally different boronated quinazolines were designed bearing 22-37% boron by weight for potential application in BNCT of tumors. Firstly, the o-carborane cage was linked to quinazoline at C-2 position via thioether linker: 2-S-(1,2-dicarba-closo-dodecaboran(12)-1-ylmethyl)-3-phenylquinazolin-4(3H)-one. Secondly, the o-carborane cage connected to quinazoline moiety at C-4 position through an ether linkage: 4-O-(o-carboran-1-ylmethyl)-2-methylquinazoline. Finally, carborane moieties were also linked to the C-6 position of quinazoline: 6-[N-{3-(2-methyl-1,2-dicarba-closo-dodecaboran(12)-1-yl)methyl}benzylidinamino]quinazolin-4(3H)-one and 6-[N-{3,5-di(2-methyl-1,2-dicarba-closo-dodecaboran(12)-1-yl)methyl}benzylidinamino]quinazolin-4(3H)-one. The water solubility was achieved by the degradative conversion of the o-carboranylquinazolines to the corresponding potassium nido-carboranyl quinazolines: 2-S-(1,2-dicarba-nido-undecacarborate-1-ylmethyl)-3-phenylquinazolin-4(3H)-one, 4-O-(1,2-dicarba-nido-undecacarborate-1-ylmethyl)-2-methylquinazoline, 6-[N-{3-(2-methyl-1,2-dicarba-nido-undecacarborate-1-yl)methyl}benzylidinamino]quinazolin-4(3H)-one and 6-[N-{3,5-di(2-methyl-1,2-dicarba-nido-undecacarborate-1-yl)methyl}benzylidinamino]quinazolin-4(3H)-one. The products were confirmed by NMR, elemental analysis, IR, and mass spectrometry. In vitro toxicity was performed with B16 melanoma cells and showed that the connection of hydrophilic nido-carborane to quinazoline moiety decreases the compound's toxicity. This cytotoxicity effect was not observed in the nido-carborane containing two cluster units which was relatively nontoxic and did not inhibit colony formation up to concentrations of 300microg boron ml(-1). The compounds described here can be considered as new candidates for BNCT.

Pub.: 15 Apr '08, Pinned: 11 Apr '17