Mass spectral method gives fast DNA analysis With the appearance of machines to mechanize production of synthetic DNA sequences, genetic engineers will need faster methods to analyze products to be sure they have made the right sequence. Plasma desorption mass spectrometry may fill this need [J. Am. Chem. Soc, 103, 1609 (1981)], Chemistry professor Ronald D. Macfarlane and research scientist Catherine J. McNeal of Texas A&M University report they have used the method to study sequences up to 18 bases long. Because they observed ions having a molecular weight of 12,637 ± 10, which they conclude was the dimer of a dodecanucleotide, they suggest that the method may be use ful for sequences as many as 25 bases long. Fragmentation patterns resemble those from enzymic breakdown of DNA strands from both ends. Their mass spectrometric method thus can be used to determine sequences of bases in DNA chains containing phosphotriester linkages. DNA strands with protecting groups or unnatural DNA analogs linked by methanephosphonate rather than phosphate esters, which are not amenable to analysis by enzymic techniques, also may be analyzed by mass spectrometry. In plasma desorption mass spec trometry, the ionization 252 source is californium-252. When a Cf nu cleus fissions into two fragments of roughly equal mass, one flies "for ward" to strike a layer of sample de posited on aluminized polypropylene film. The other recoils "backward," and its detection starts a clock. The first fragment transfers about 1013 watts per sq cm to the sample within one picosecond. This sudden energy transfer vaporizes and ionizes part of the sample before any heating effect decomposes the molecules. Resulting ions accelerate through a time-offlight mass spectrometer. A computer calculates ion masses from times needed to reach the detector in com parison with the time when the 252Cf recoil fragment starts the clock. The DNA sequence that yielded the high-molecular-weight dimer was in a form that commonly results from synthesis on gene machines. Adenine and cytosine were protected by ben zoyl groups, guanine by isobutyryl groups, and phosphate hydroxyls by ρ -chlorophenyl groups. Macfarlane and McNeal suggest
For sale. Research laboratories, offices and workshops complex in the neighbourhood of Arnhem, The Netherlands. The site within which the complex is situated is 35 ha. of which 32 ha. is in agriculture use. The buildings where designed as laboratories, offices, pilot plant, warehouses and workshops but can easily be adapted for other purposes. The buildings are designed and constructed to a high standard and are well maintained. The services which include air conditioning are technic.ally of a high quality. Floor loadings offices 500 kg/m 2 . Floor loadings pilot plant, workshops 1.000/1.500 kg/m 2 . The restaurant is fully equipped. Car parking for approximately 100 cars. There are facilities within the complex for the extension of the buildings. Totally 9 buildings with gross areas 10.530 m2 and net areas 7.715 m2, 2.100 m2 greenhouses and a farm house. Detailed report is available.
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April 27, 1981 C&EN 23
Announcing . .. An ACS Summer Institute for College Teachers
Science plore the upper limits of detection by their technique, although larger se quences may be amenable to analysis. They say they would accept samples from academic investigators and private firms for such sequence analyses. Their work in this field has been supported by the National Institute of General Medical Sciences, the National Science Foundation, and the Robert A. Welch Foundation. D
that the 12,637 ± 10 mass ion they detected was a dimer of the dodecanucleotide they used, associated with four sodium atoms. In addition to the parent dodecanucleotide mass 6301 ± 3 ion, they also saw a mass at 8709 ± 8, which they conclude is a fragment of the dimer. The Texas A&M workers say no one has yet sent them a synthetic sequence longer than 18 bases, so they have not had a chance to ex
Aldol modification yields high optical purities June 21-30,1981 At Syracuse University, Syracuse, New York Partially supported by a grant from the ACS Education Commission The Institute will feature lec ture and hands-on laboratory experience with microcompu ters and related devices. Regis tration will be limited to the first 39 applicants. WHO SHOULD ATTEND The Institute is designed for col lege chemistry teachers who are computer novices—particular ly faculty of two- or four-year colleges or university faculty whose primary responsibility i$ undergraduate teaching.
Asymmetry in mandelic acid derivative
COSTS The tuition fee is $50.00. All meals, at a cost of $119.00 per participant, will be provided at a Syracuse University dining facility. Lodging is available either at a university dormitory or at a nearby motel.
For example, in work with post doctoral students William Choy and Francis A. J. Kerdesky and graduate student Barbara Imperiali, Masamune hydrogenated an optical isomer of majidelic acid to the cyclohexylhydroxyacetic acid, which gave 1cyclohexyl-l-hydroxy-2-butanone with ethyllithium, and then a 1-tertbutyldimethylsilyloxy derivative on silylation. To activate the propionyl group in these compounds for the aldol reac tion, the MIT workers treated the compounds with dicyclopentylborinyl or 9-borabicyclo[3,3,l]nonan-9-yl trifluoromethanesulfonates (triflates) to form dialkylborinylenolates. They carried out the aldol condensation with such aldehydes as propionaldehyde, desilylated the adduct with hydrogen fluoride, and oxidized to /3-hydroxy-a-methyl acid products. Yields were 70 to 85%, and optical purities ranged from 93 to more than 99%. D
Optical purities of almost 100% result from a method of carrying out aldol reactions developed by organic chemistry professor Satoru Masamune and his coworkers at Massa chusetts Institute of Technology [J. Am. Chem. Soc, 103, 1566 (1981)]. Their technique could ease laboratory production of such natural products as large-ring antibiotics. The group already has applied the method to making the erythromycin derivative 6-deoxyerythronolide B, whose total synthesis had been achieved earlier by collaborators of organic chemistry professor Elias J. Corey of Harvard University (C&EN, July 10,1978, page 25). In work supported by the National Institutes of Health, the MIT group made a dialkylborinylenolate of a mandelic acid derivative. The com mercial availability of either optical isomer of mandelic acid at $1.35 to $1.75 per gram adds attraction to the synthesis.
?(CH )
3 3
CH 3 CH,
Hs
CH,3s
J3Si(CH 3 ) 2
(Or ΥΌ C
+
OS02CF3—*
Active ketone
Borinyl trifflate
H'
~HO) V - ' H T)Si(CH 3 ) 2 C(CH3)3 Borinylenolate
gives almost 100% optical purity in products TO REGISTER For a descriptive flyer and reg istration form, write or call the Education Department, Ameri can Chemical Society, 1155 Six teenth Street, N.W., Washing ton, DC 20036; telephone 202872-4508.
24
C&EN April 27, 1981
Ç(CH3)3 CH3
CH3CH2CHO «
Propionaldehyde
w
CH3CH2
Η V C
OH
Ο
CH,
OSi(CH3)2 C
CH,CH
» C \ !/ iv C A C0 2 H OH
Active acid 70 to 85% yield >99% optical purity
