Synthesis of a novel C-nucleoside, 2-amino-7-(2-deoxy-beta-D-erythro- pentofuranosyl)-3H,5H-pyrrolo-[3,2-d]pyrimidin-4-one (2'-deoxy-9-deazaguanosine).

A synthesis of the C-nucleoside, 2-amino-7-(2-deoxy-beta-D-erythro- pentofuranosyl)-3H,5H-pyrrolo[3,2-d]pyrimidin-4-one (9-deaza-2'-deoxyguanosine) was achieved starting from 2-amino-6-methyl-3H-pyrimidin-4-one (5) and methyl 2-deoxy-3,5-di-O-(p-nitrobenzoyl)-D-erythro-pento-furanoside (11). The anomeric configuration of the C-nucleoside was established by 1H NMR, NOEDS and ROESY. This C-nucleoside did not inhibit the growth of T-cell lymphoma cells.

Bicyclic monoterpene diols induce differentiation of S91 melanoma and PC12 pheochromocytoma cells by a cyclic guanosine-monophosphate-dependent pathway.

Previously, we showed that 5-norbornene-2,2-dimethanol (5-NBene-2,2-DM) is an effective inducer of melanogenesis in cultured cells and guinea-pig skin [Brown et al. (1998) J. Invest. Dermatol., 110:428-437]. This study shows that 2,3-cis/exo-pinanediol (2,3-cs/ex-PinD) is a more effective inducer of melanogenesis than 5-NBene-2,2-DM in S91 mouse melanoma cells. Furthermore, 2,3-cs/ex-PinD appears to penetrate guinea-pig skin better than 5-NBene-2,2-DM and to induce higher levels of pigmentation. Both 5-NBene-2,2-DM and 2,3-cs/ex-PinD induce synthesis of nitric oxide (NO) in S91 cells, and the melanogenic activity of both compounds is reduced by inhibitors of the NO/cyclic guanosine monophosphate (cGMP)/protein kinase(PK) G signaling pathway, but not by inhibitors of the PKC or PKA pathways. Thus, these bicyclic monoterpene diols appear to induce melanogenesis by the same pathway in S91 cells as that shown previously for ultraviolet radiation in melanocytes (Romero-Graillet et al. (1996) J. Biol. Chem., 271:28052-28056). These compounds also induce NO synthesis, neurite outgrowth, and tyrosine hydroxylase activity in PC12 pheochromocytoma cells. Neurite outgrowth in PC12 cells is blocked by the guanylate cyclase inhibitor, LY83583 (6-anilino-2,8-quinolinequinone), indicating that, similar to S91 cells, the induction of morphological differentiation of PC12 cells by bicyclic monoterpene diols is regulated by a cGMP-dependent pathway.

A pseudosquare knot structure of DNA in solution.

We report a high-resolution NMR structure of a homodimer formed by a synthetic 25 residue DNA oligonucleotide GCTCCCATGGTTTTTGTGCACGAGC. This structure presents a novel structural motif for single-stranded nucleic acids, called a pseudosquare knot (PSQ). The oligonucleotide was originally designed to mimic a slipped-loop structure (SLS), another "unusual" DNA structure postulated as an alternative conformation for short direct repeats in double-stranded DNA. The design of the sequence is compatible with both SLS and PSQ structures, both of which possess identical sets of base-paired and unpaired nucleotides but different tertiary folds. We used deuteration of the H8 positions of purines to ascertain that the PSQ is actually formed under the conditions used. The PSQ structure was solved based on homonuclear proton nuclear Overhauser effect data using complete relaxation matrix methods. The structure essentially consists of two side-by-side helices connected by single-stranded loops. Each of the helices is well-defined; however, the relative orientation of the two remains undetermined by the NMR data. The sequences compatible with the PSQ formation are frequent in single-stranded genomes; this structure may play a role as a dimerization motif.

Nuclear magnetic resonance structure of d(GCATATGATAG). d(CTATCATATGC): a consensus sequence for promoters recognized by sigma K RNA polymerase.

The three-dimensional structure of d(GCATATGATAG).d(CTATCATATGC), from the promoter region of a gene regulating sporulation in Bacillus subtilis mother cells, was determined utilizing two-dimensional nuclear Overhauser effect (2D NOE) and double-quantum-filtered COSY (2QF-COSY) spectra. To minimize the effect of methods used to obtain restraints and refine structure, several variables were studied. Interproton distance bounds were calculated very conservatively by running the complete relaxation matrix program MARDIGRAS hundreds of times using 2D NOE spectra for exchangeable and for nonexchangeable protons at different mixing times, assuming different overall correlation times and different starting structures. The 435 distance restraints were used with two different structural refinement methods: restrained molecular dynamics (rMD) and restrained Monte Carlo calculations (rMC). Refinement using different procedures and starting structures resulted in essentially the same structure (<0.8 A rmsd), indicating that the structure is defined by experimental restraints and not the refinement method or variables used. R factors indicate the structures fit the experimental NOE data very well. Some helical parameters, notably large negative X displacement, are characteristic of A-DNA, but others are characteristic of B-DNA. As with TG.CA steps in other duplex DNA sequences studied in our laboratory, the two TG.CA steps have a positive roll, with T6-G7 exhibiting the largest, and consequently a bent helix axis. The converged structure represents a time-averaged structure. However, multiple conformations, especially in deoxyriboses, were evident from vicinal coupling constants obtained from quantitative simulations of 2QF-COSY cross-peaks and from persistent inconsistencies in experimental distances due to nonlinear conformational averaging.

Aliphatic and alicyclic diols induce melanogenesis in cultured cells and guinea pig skin.

We have found that several aliphatic and alicyclic diols induce melanogenesis in cultured S91 mouse melanoma cells and normal human epidermal melanocytes (NHEM). In addition, these compounds induce melanogenesis when applied to guinea pig skin, with transfer of melanin to keratinocytes and formation of "supranuclear caps," as occurs in naturally pigmented skin. The relative order of potency of some of these diols in NHEM is 5-norbornene-2,2-dimethanol > 3,3-dimethyl-1,2-butanediol > cis-1,2-cyclopentanediol > 2,3-dimethyl-2,3-butanediol > 1,2-propanediol. Following treatment with these diols or 3-isobutyl-1-methylxanthine, melanin and tyrosinase activity are increased within S91 cells and NHEM; however, for cultured NHEM, the largest increases of melanin and tyrosinase occur in an extracellular particulate fraction, shown by electron microscopy to consist almost entirely of stage III and IV melanosomes. These results indicate that cultured NHEM treated with diols export melanosomes in a fashion that is commensurate with natural melanogenic processes. In contrast, S91 mouse melanoma cells exhibit aberrant melanosomal trafficking, in accordance with the known defect in myosin-V mediated melanosomal transport. Both S91 cells and NHEM exhibit morphologic changes and growth arrest indicative of differentiation following treatment with diols. The diols described in this report are candidates for use as cosmeceutical tanning agents.

Synthesis of a methylenebis(phosphonate) analogue of mycophenolic adenine dinucleotide: a glucuronidation-resistant MAD analogue of NAD.

Mycophenolic alcohol (MPAlc), obtained by reduction of the carboxylic group of mycophenolic acid (MPA), was coupled with 2',3'-O-isopropylideneadenosine 5'-methylenebis(phosphonate) (4) in the presence of diisopropylcarbodiimide (DIC) to give P1-(2',3'-O-isopropylideneadenosin-5'-yl)-P2-(mycophenolic alcohol-6'-yl)methylenebis(phosphonate) (8) in 32% yield. Deisopropy-lidenation of 8 with CF3COOH/H2O afforded the methylenebis(phosphonate) analogue 3 of mycophenolic adenine dinucleotide (MAD). Compound 3, beta-methylene-MAD, was found to be a potent inhibitor of inosine monophosphate dehydrogenase (IMPDH) type II (Ki = 0.3 microM) as well as an inhibitor of growth of K562 cells (IC50 = 1.5 microM). In contrast to MPA and mycophenolic alcohol, beta-methylene-MAD was not converted into the glucuronide when incubated with uridine 5'-diphosphoglucuronyltransferase.

Synthesis of nonhydrolyzable analogues of thiazole-4-carboxamide and benzamide adenine dinucleotide containing fluorine atom at the C2' of adenine nucleoside: induction of K562 differentiation and inosine monophosphate dehydrogenase inhibitory activity.

Thiazole-4-carboxamide adenine dinucleotide (TAD) analogue 7 containing a fluorine atom at the C2' arabino configuration of the adenine nucleoside moiety was found to be a potent inducer of differentiation of K562 erythroid leukemia cells. This finding prompted us to synthesize its hydrolysis-resistant methylenebis(phosphonate) and difluoromethylenebis(phosphonate) analogues 8 and 9, respectively. Since both TAD and benzamide adenine dinucleotide (BAD) are potent inhibitors of inosine monophosphate dehydrogenase (IMPDH), the corresponding fluorine-substituted methylenebis(phosphonate) analogue 12 of BAD was also synthesized. Thus, 9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)adenine (13) was converted in five steps into the corresponding methylenebis(phosphonate) analogue 18. Dehydration of 18 with DCC led to the formation of the bicyclic trisanhydride intermediate 19a, which upon reaction with 2',3'-O-isopropylidenetiazofurin (20) or -benzamide riboside (21) followed by hydrolysis and deprotection afforded the desired methylene-bridged dinucleotides 8 and 12, respectively. The similar displacement of the 5'-mesyl function of 2',3'-O-isopropylidene-5'-O-mesyltiazofurin (24) with the difluoromethylenebis(phosphonic acid) derivative gave the phosphonate 25 which was coupled with 13 to afford 26. The desired difluoromethylenebis(phosphonate) analogue 9 was obtained by deprotection with Dowex 50/H+. This compound as well as beta-CF2-TAD (4) showed improved differentiation-inducing activity over beta-CH2-TAD (3), whereas analogues containing the -CH2-linkage (8 and 12) were inactive.

The solid-phase synthesis of 2'-5'-linked oligoriboadenylates containing 8-bromoadenine.

To increase the accessibility of 8-bromo-2',5'-oligoadenylates, we developed a synthesis of 2'-5'-linked oligoriboadenylates containing varying numbers of 8-bromoadenosine residues based on the use of a CPG-LCA solid support and the phosphoramidite approach. Although N6-benzoyl protection was satisfactory for incorporation of nonmodified adenine residues into 2',5'-oligonucleotides, the effective incorporation of 8-bromoadenine into such 2',5'-linked oligomers required use of a non acyl protecting group. Amidine protection of the purine exocyclic amino function proved compatible with all aspects of the phophoramidite approach and with the hydroxyl protection groups employed.

The practical synthesis of a methylenebisphosphonate analogue of benzamide adenine dinucleotide: inhibition of human inosine monophosphate dehydrogenase (type I and II).

beta-Methylene-BAD (8), a nonhydrolyzable analogue of benzamide adenine dinucleotide (BAD), was synthesized as potential inhibitor of human inosine monophosphate dehydrogenase (IMPDH). Treatment of 2',3'-O-isopropylideneadenosine 5'-methylenebisphosphonate (15) with DCC afforded P1,P4-bis(2',3'-O-isopropylideneadenosine) 5'-P1,P2:P3,P4-dimethylenetetrakisphosphonate (17). This compound was further converted with DCC to an active intermediate 18 which upon reaction with 3-(2',3'-O-isopropylidene-beta-D-ribofuranosyl)benzamide (19) gave, after hydrolysis and deisopropylidenation, the desired beta-methylene-BAD (8) in 95% yield. In a similar manner, treatment of 18 with 2',3'-O-isopropylidenetiazofurin (21) followed by hydrolysis and deprotection afforded beta-methylene-TAD (5) in 91% yield. Compound 8 (IC50 = 0.665 microM) was found to be a 6-8 times less potent inhibitor of IMPDH than 5 (IC50 = 0.107 microM) and was almost equally potent against IMPDH type I and type II. Although TAD and beta-methylene-TAD were bound by LADH with the same affinity, the binding affinity of 8 toward LADH (Ki = 333 microM) was found to be 50-fold lower than that of the parent pyrophosphate 7 (Ki = 6.3 microM).

Efficient functionalization of 2',5'-oligoadenylates with sulfur.

To derivatize the 2'-terminus of 2',5'-oligoadenylates with a thiol group, the reaction of periodate-oxidized nucleotide and 2',5'-oligonucleotide with aminothiols was explored. Two separate synthetic approaches were employed, both of which relied upon the use of S-protected thiols. In one approach, 5'AMP was oxidized with sodium periodate to dialdehyde, which was reacted with cystamine hydrochloride. Sodium cyanoborohydride reduction of the unisolated intermediate animal gave compound 4. The second approach involved reaction of S-(2-tetrahydropyranyl)cysteamine with the dialdehyde obtained by periodate oxidation of 5'AMP to yield, after reduction with Na(CN)BH3, the S-protected adduct 3. Intermediate 3 could be oxidized with aqueous iodine to give disulfide 4. Disulfide 4, obtained by either of the above routes, was reduced with dithiotreitol (DTT) to the thiol 5. This same reaction sequence was applied to 2-5A tetramer monophosphate, p5'A2'[p5'A2']2p5'A (6a), to give via 6b the 2'-terminal-modified derivative 6c. Aqueous iodine oxidation of 6c provided the disulfide 7, which reacted with DTT to give quantitative conversion to product, the free thiol 8. Both the disulfide 7 and the S-tetrahydropyranyl-protected derivative (6c) were bound effectively to the 2-5A-dependent RNase L of mouse L cells with IC50 values of 1 x 10(-9) M for 7 and 8 x 10(-10) M for 6c, not significantly different from the corresponding value for the parent unmodified 2-5A (6a) itself.

Synthesis and characterization of composite nucleic acids containing 2', 5'-oligoriboadenylate linked to antisense DNA.

Composite nucleic acids, known as 2-5A antisense chimeras, cause the 2-5A-dependent ribonuclease (RNase L) to catalyze the specific cleavage of RNA in cell free systems and in intact cells. Such 2-5A antisense chimeras are 5'-monophosphorylated, 2,'5'-linked oligoadenylates covalently attached to antisense 3',5'-oligodeoxyribonucleotides by means of a linker containing two residues of 1,4-butanediol phosphate. Here we report a fully automated synthesis of 2-5A antisense chimeras on a solid support using phosphoramidite methodology with specific coupling time modifications and their subsequent purification by reverse-phase ion-pair and anion exchange HPLC. Purified 2-5A antisense chimeras were characterized by [1H]NMR and [31P]NMR, MALDIMS, and capillary gel electrophoresis. The synthetic 2',5'-linked oligoadenylate showed no phosphodiester isomerization to 3',5' during or after synthesis. In addition, we have developed facile methodologies to characterize the chimeras using digestion with various hydrolytic enzymes including snake venom phosphodiesterase I and nuclease P1. Finally, Maxam-Gilbert chemical sequencing protocols have been developed to confirm the entire sequence of these chimeric oligonucleotides.

Analysis of Neisseria meningitidis class 3 outer membrane protein gene variable regions and type identification using genetic techniques.

The class 3 porin proteins of Neisseria meningitidis stimulate bactericidal antibodies and express serotype-specific antigenic epitopes. Sequence analysis of porB genes for the class 3 proteins revealed regions of variability that map to surface-exposed loops. To evaluate the relationship between serotype and variable-region (VR) genotype, sequences from the 11 class 3-expressing serotype strains and 3 additional serotype 4 strains were analyzed by molecular techniques. Multiple-sequence alignment revealed a limited number of unique sequences at each of four VRs (VR1 to VR4), ranging from four unique sequences at VR1 to seven sequence patterns at VR2 and VR4. Serotype-specific VR sequences were found in each of the four VRs, suggesting that each VR has immunologic importance. Five serotypes had at least one VR sequence that was unique. Three serotypes which had sequences in common with other serotypes at each VR were distinguished by examining multiple VRs. Serotype 3 was identical to serotype 19 at each VR, and serotype 8 was identical to serotype 18 at each VR. Serotypes 4 and 21 were identical at VR1 and significantly different at VR3 and VR4. A subpopulation of serotype 4 strains with a unique VR2 sequence was identified. The serotypes which were grouped with closely related or identical sequences at one VR were grouped with different serotypes at other VRs consistent with the pattern of genetic mosaicism described for the porA (class 1 protein) gene. Hybridization assays demonstrated the ability to identify VR genotypes and distinguish serotypes using biotin-labelled oligonucleotide probes. This information may be useful in strain selection for vaccine development, in epidemiologic studies to determine the prevalence of the individual VR genotype (especially among nonserotypeable strains) and, combined with PCR, in the identification of culture-negative suspected meningococcal cases.

[Clinical and electrophysiological examination of brachial plexus in females after radiotherapy and surgical treatment for breast cancer]. / Kliniczna i elektrofizjologiczna ocena splotu barkowego u kobiet po zastosowaniu promieniowania jonizujacego w uzupelniajacym leczeniu raka sutka.

Clinical and electrophysiological examinations of the brachial plexus was carried out in 61 women after radiotherapy following operation for breast cancer. A number of clinical abnormalities were found such as hypeaesthesia, hyporeflexia, muscular atrophy, lymphoedema of the extremity which were confirmed by electrophysiological examination. The most common findings were of neurogenic muscular atrophy in the involved extremity, less frequent was slower nerve conduction on the affected side. The analysis of the results suggested mixed type of brachial plexus lesions diagnosed in these cases as late brachial plexopathy.

2',5'-Oligoadenylate:antisense chimeras--synthesis and properties.

We have synthesized a novel bioconjugate which joins an antisense oligonucleotide to a unique and potent inhibitor of translation,pn5'A2'(p5'A2')mp5'A(2-5A). Two residues of 4-hydroxybutyl phosphate were employed as linkers to attach the 2',5'-oligoadenylate moiety through its 2'-terminus to the 5'-terminus of the chosen antisense sequence, (dT)20. The syntheses were carried on a solid support according to the phosphite triester method of DNA synthesis (Letsinger, R.L., Lunsford, W.B. (1976) J. Am. Chem. Soc. 98, 3655-3661; Beaucage, S.L., and Caruthers, M.H. (1981) Tetrahedron Lett. 22, 1859-1862). The generated 2-5A antisense chimeras retained both the ability of the 2-5A molecule to activate the 2-5A-dependent RNase as well as the ability of the oligo(dT) moiety to hybridize to the complementary poly(A). Moreover, the chimera, when annealed to its target nucleic acid sequence, was still effectively bound to the 2-5A-dependent nuclease. The methodology described represents a new approach to the selective modulation of mRNA expression.

Targeting RNA for degradation with a (2'-5')oligoadenylate-antisense chimera.

Antisense oligonucleotides hold considerable promise both as research tools for inhibiting gene expression and as agents for the treatment of a myriad of human diseases. However, targeted destruction of RNA has been difficult to achieve in a versatile, efficient, and reliable manner. We have developed an effective strategy for cleaving unique RNA sequences with 2-5A-dependent RNase, an endoribonuclease that mediates inhibitory effects of interferon on virus infection and is activated by 5'-phosphorylated 2'-5'-linked oligoadenylates known as 2-5A [pn5' A2'(p5' A2')mp5'A], resulting in the cleavage of single-stranded RNA predominantly after UpUp and UpAp sequences. To direct 2-5A-dependent RNase to cleave unique RNA sequences, p5' A2' p5' A2'p5'A was covalently linked to an antisense oligonucleotide to yield a chimeric molecule (2-5A:AS). The antisense oligonucleotide component of 2-5A:AS bound a specific RNA sequence while the accompanying 2-5A component activated 2-5A-dependent RNase, thereby causing the cleavage of the RNA in the targeted sequence. This strategy was demonstrated by inducing specific cleavage within a modified human immunodeficiency virus type 1 vif mRNA in a cell-free system from human lymphoblastoid cells. Because 2-5A-dependent RNase is present in most mammalian cells, the control of gene expression based on this technology--including therapies for cancer, viral infections, and certain genetic diseases--can be envisioned.

A new and potent 2-5A analogue which does not require a 5'-polyphosphate to activate mouse L-cell RNase L.

In order to explore the possibility of supplanting the requirement of a 5'-triphosphate moiety for the activation of the 2-5A-dependent endonuclease (RNase L) of mouse L-cells, two new tetrameric analogues of 2-5A were synthesized. The first tetramer, obtained by both a modified prebiotic synthetic approach as well as a phosphite triester solid phase oligonucleotide synthesis method, was p5'A2'p5'A2'p5'(br8A)2'p5'(br8A). The second oligonucleotide was derived from the former by a sequence involving periodate oxidation, reaction with n-hexylamine, and cyanoborohydride reduction, resulting in conversion of the 2'-terminal adenosine residue to 9-(3'-aza-4'-hexyl-1',2',3',4'-tetradeoxyhexopyranos-1(1)-yl)-8-++ +bromoadenine. Both of these oligomers, bearing only 5'-monophosphate groups, were found to be as potent as 2-5A itself as activators of the RNase L of mouse L-cells.

Synthesis and biological activity of uronic acid analogues of 2-5A[5'-O-triphosphoryladenylyl(2----5')adenylyl-(2'----5')adenosine].

The oligonucleotide ppp5'A2'p5'A2'p5'A, known as 2-5A, is a potent translational inhibitor involved in some aspects of interferon action. To explore the specific function of the charged 5'-triphosphate moiety, we prepared a series of congeners in which the 5' region was hypermodified. Thus, uronic acid derivatives were substituted for the 5' terminal adenosine residue of 2-5A. Compounds 9, 10, 11 and 12 carried adenosine 5'-uronic acid, ethyl adenosine 5'-uronate, adenosine 5'-uronamide, and adenosine 5'-(N-ethyl)uronamide, respectively, in place of the 5' terminal adenosine triphosphate moiety of 2-5A. While all the analogues showed some weak interaction with the 2-5A-dependent endonuclease (RNase L), compound 9 showed the strongest binding ability, and while unable to activate the mouse RNase L, could activate human RNase at a concentration 100-fold greater than that required for the parent 2-5A. This result suggests that the function of the 5'(poly)phosphate moiety of 2-5A may be fulfilled by some other anionic moiety.

2',5'-oligoadenylates inhibit relaxation of supercoiled DNA by calf thymus DNA topoisomerase I.

DNA topoisomerases interconvert various topological isomers of DNA and play key roles in replication and gene expression. The possible involvement of the 2',5'-oligoadenylates (2-5A) system in cell growth, regulation, and cell differentiation led us to investigate the effects of 2-5A on mammalian topoisomerases. We found that the calf thymus type I topoisomerase was inhibited by a variety of 2-5A compounds. The level of inhibition was dependent upon the number of residues and the degree of phosphorylation at the 5' terminus. The 5'-triphosphorylated 2',5' hexamer, ppp(Ap)5A, was the most effective, strongly reducing relaxation at less than micromolar concentrations. These results raise the possibility that physiological concentrations of 2-5A of sufficient chain length may be capable of regulating gene expression by virtue of a direct inhibition of DNA topoisomerase I.

Mechanism of HIV reverse transcriptase: enzyme-primer interaction as revealed through studies of a dNTP analogue, 3'-azido-dTTP.

Primer and dNTP recognition by purified HIV reverse transcriptase have been investigated. Earlier kinetic studies suggested that the reaction pathway for DNA synthesis is ordered, with template-primer and free enzyme combining to form the first complex in the reaction sequence [Majumdar et al. (1988) J. Biol. Chem. 263, 15657-15665], and through use of a particularly high affinity template-primer analogue [r(I)n.Sd(C)28], rate values for formation of the first complex were calculated [Majumdar et al. (1989) Biochemistry 28, 1340-1346]. We now report rate values for first complex formation in the usual model replication system with poly[r(A)].oligo [d(T)] as template-primer. We find that 3'-azido-dTTP (AZTTP) is a linear competitive inhibitor of DNA synthesis against the substrate dNTP (dTTP) in the poly[r(A)].oligo[d(T)] replication system. This suggests that 3'-azido-dTTP and dTTP combine with the same form of the enzyme in the reaction scheme, i.e., the enzyme-primer complex. This is not trivial, since a second analogue, 3'-amino-dTTP, also is an inhibitor against dTTP, but the mechanism in this case is linear noncompetitive. Because the inhibition by 3'-azido-dTTP is linear competitive, the KD for physical binding to the enzyme is assumed to be the same as the Ki for inhibition (20 nM). Substrate kinetic studies of DNA synthesis using 3'-azido-dTTP as substrate revealed that the Michaelis constant is 3 microM. Therefore, the Km for this substrate analogue is 100-fold higher than the KD for binding of the analogue to the enzyme-primer complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation of alpha-deoxyadenosine in polydeoxynucleotides exposed to ionizing radiation under anoxic conditions.

When poly(dA), poly(dA-dT), and salmon testis DNA were gamma-irradiated under nitrogen, the major deoxyadenosine damage product (excluding liberated adenine) was identified as the alpha-anomer of deoxyadenosine. The yields of alpha-deoxyadenosine from poly(dA), poly(dA-dT), and salmon testis DNA irradiated with a dose of 500 Gy under anoxic conditions were 1.5, 1.3, and 1.3%, respectively. No alpha-deoxyadenosine was detected after irradiation under oxic conditions. The presence of nucleotides with the alpha-configuration at the anomeric carbon atom in the DNA chain may have a significant effect on its tertiary structure and possibly modify its biological activity.