Cognitive consequences and central nervous system injury following treatment for childhood leukemia.

OBJECTIVES: To determine the relationship between membrane damage and intellectual and academic abilities in children with acute lymphoblastic leukemia (ALL) and pilot test a math intervention for children with ALL who were affected. DATA SOURCES: Research studies and review articles. CONCLUSIONS: Despite the prophylactic central nervous system (CNS) treatment for long-term disease-free survival, many children with ALL subsequently experience declines in intellectual and academic skills. IMPLICATIONS FOR NURSING PRACTICE: Improving academic abilities in children who have received CNS treatment is of high priority and may have longlasting implications on quality of life.

Design and synthesis of conformationally constrained glucagon analogues.

Glucagon was systematically modified by forming lactam bridges within the central region of the molecule to give conformationally constrained cyclic analogues. Six cyclic glucagon analogues have been designed and synthesized. They are c[Asp(9),Lys(12)][Lys(17,18), Glu(21)]glucagon-NH(2) (1), c[Asp(9),Lys(12)]glucagon-NH(2) (2), c[Lys(12),Asp(15)]glucagon-NH(2) (3), c[Asp(15), Lys(18)]glucagon-NH(2) (4), [Lys(17)-c[Lys(18), Glu(21)]glucagon-NH(2) (5), and c[Lys(12),Asp(21)]glucagon-NH(2) (6). The receptor binding potencies and receptor second messenger activities were determined by radio-receptor binding assays and adenylate cyclase assays, respectively, using rat liver plasma membranes. Most interestingly, analogues 1, 2, 3, and 4 were antagonists of glucagon stimulated adenylate cyclase activity, whereas analogues 5 and 6 were partial agonists in the functional assay. All of the cyclic analogues were found to have reduced binding potencies relative to glucagon. The structural features that might be responsible for these effects were studied using circular dichroism spectroscopy and molecular modeling. These results demonstrated the significant modulations of both receptor binding affinity and transduction (adenylate cyclase activity) that can accompany regional conformational constraints even in larger polypeptide ligands. These studies suggest that the entire molecular conformation, including the flexible middle portion, is important for molecular recognition and transduction at the hepatic glucagon receptor.

Synthesis of thiazole-4-carboxamide-adenine difluoromethylenediphosphonates substituted with fluorine at C-2' of the adenosine.

Synthesis of an analogue 3 of thiazole-4-carboxamide adenine-dinucleotide (TAD) in which the beta-oxygen atom of the pyrophosphate bridge is replaced by a difluoromethylene group has been achieved. Likewise, 2'-deoxy-2'-fluoroadenosine containing analogues of TAD (4) and its difluoromethylenediphosphonate congener (5) have been synthesized. Adenosine 5'-difluoromethylenediphosphonate (8) was prepared from 5'-O-tosyladenosine (6) and tris(tetra-n-butylammonium)difluoromethylenediphosphonate (7) by a modified procedure of Poulter's. Compound 8 was converted into the 2',3'-cyclic carbonate 9 by treatment with triethyl orthoformate. Treatment of 9 with 2',3'-O-isopropylidenetiazofurin (10) in pyridine in the presence of DCC gave a mixture of dinucleotide 11 and the isopropylidene-protected diadenosine tetraphosphonate 12. After deprotection of 11, the desired beta-difluoromethylene TAD (3) was separated by HPLC as the minor product. The diadenosine tetraphosphonate 12, an analogue of Ap4A, was obtained as the major component. Alternatively, 2',3'-O-isopropylidenetiazofurin (10) was tosylated, and the product 13 was further converted into the corresponding difluoromethylenediphosphonate 14 by coupling with 7. DCC-catalyzed coupling of 14 with 2'-deoxy-2'-fluoroadenosine (15) followed by deisopropylidenation afforded the analogue 5. Again the corresponding tetraphosphonate analogue of tiazofurin 17 was the predominant product. Dinucleotide 4 was obtained by coupling of the carbonyldiimidazole-activated tiazofurin 5'-monophosphate with 2'-deoxy-2'-fluoroadenosine 5'-monophosphate. 2'-Deoxy-2'-fluoroadenosine (15) was prepared efficiently from the known N6-benzoyl-3'-O-tetrahydropyranyladenosine (18), which was converted into 3'-O-tetrahydropyranyl-2'-O-triflyl-5'-O-trityladenosine (20) by tritylation and triflation. Treatment of 20 with sodium acetate in hexamethylphosphoric triamide, followed by deacetylation afforded 9-(3-O-tetrahydropyranyl-5-O-trityl-beta-D- arabinofuranosyl)-N6-benzoyladenine (22), which was then treated with DAST. After deprotection of the product, 15 was obtained in good yield.

Synthetic linear and cyclic glucagon antagonists.

The synthesis and biological activities of seven new glucagon analogues are reported. The design of compounds 2-5 is based on potent antagonists recently reported from this laboratory, where we have focused on modifications in the N-terminal region. In this report we have concentrated specifically on modifications to histidine-1. In addition we have prepared two cyclic compounds 7 and 8, related to a linear in vivo antagonist [Glu9]glucagon, reported by Merrifield (Unson et al. (1987) Proc. Natl. Acad. Sci. USA 84, 4083-4087). The N-terminal modifications involved substitution of His1 by the unnatural conformationally constrained residue (S)-5,6,7,8-tetrahydro-5-oxoimidazo(1,5-c)pyrimidine-7-carboxylic acid (Toc), desaminohistidine (dHis) and 3-(4-nitrobenzyl)histidine. The structures of the new compounds are as follows. [Toc1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon (2); [Toc1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon amide (3); [3-(4-nitrobenzyl)His1,D-Phe4,Tyr5,Arg12,Lys17,18,G lu21]glucagon (4); [dHis1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon (5); [dHis1,Glu9]glucagon (6); (desHis1)[Glu9,Lys12]glucagon amide (7); (desHis1)-[Glu9,Lys12,Asp15]glucagon amide (8). The binding potencies of the linear analogues, as expressed a percentage of glucagon binding, are 2.6 (2), 0.13 (3), 0.8 (4), 0.8 (5), 2.2 (6). Both cyclic analogues 7 and 8 show biphasic binding curves. The IC50 values for 7 at the high and low affinity sites are 1.5 and 167 nM, respectively (IC50 of glucagon = 1.3 nM). The IC50 values for 8 at the high and low affinity sites are 4.7 and 3451 nM, respectively. The cyclic analogues are characterized by fast atom bombardment mass spectrometry of endoproteinase ASP-N digests. The specificity of the enzyme used in these studies enables differentiation of isomers of the cyclic glucagon analogues which differ only in the position of cyclic amide bond. Analogues 2, 3 and 5-8 are glucagon receptor antagonists with respect to the glucagon receptor coupled to the adenylate cyclase (AC) system. Analogue 4 is a partial agonist (5.7% compared to glucagon) of AC. Introduction of unusual amino acids which do not contain a primary alpha-amino group such as Toc at the N-terminus is expected to increase in vivo metabolic stability by protecting against degradation by aminopeptidases.

Characterization of linear and cyclic glucagon analogs by fast atom bombardment mass spectrometry.

Fast atom bombardment mass spectral mapping of endoproteinase Asp-N digest mixtures is used for characterization of new synthetic linear and cyclic glucagon analogs. The results allow rapid identification of sequence modifications in linear glucagon analogs. For the cyclic compounds, the technique allows confirmation of the presence and position of the cyclic amide bond, as well as verification of the sequence of the modified glucagon analogs. The specificity of the Asp-N enables differentiation of isometric glucagon analogs which differ only in the position of the cyclic amide bond. Important information concerning the purity of the synthetic analogs is also available.

Chemical ionization mass spectrometry of valepotriates using isobutane as reactant gas.

A series of known valepotriates isolated from some VALERIANA species and their transformation products have been studied by CIMS (isobutane). The compounds have been characterized by molecular and protonated molecular ions and some typical fragments. Some information about the location of the acyloxy substituents, especially as regards monoene valepotriates, has been obtained.