Getting started with webchem

The lc50 dataset provided with webchem contains acute ecotoxicity of 124 insecticides. We’ll work with a subset of these to obtain chemical names and octanal/water partitioning coefficients from PubChem, and gas chromatography retention indices from the NIST Web Book.

Getting Identifiers

Usually a webchem workflow starts with translating and retrieving chemical identifiers since most chemical information databases use their own internal identifiers.

First, we will covert CAS numbers to InChIKey identifiers using the Chemical Translation Service. Then, we’ll use these InChiKeys to get Pubchem CompoundID numbers, to use for retrieving chemical properties from PubChem.

lc50_sub$inchikey <- unlist(cts_convert(lc50_sub$cas, from = "CAS", to = "InChIKey", match = "first", verbose = FALSE))
head(lc50_sub)
#>        cas        value                    inchikey
#> 4  50-29-3    12.415277 YVGGHNCTFXOJCH-UHFFFAOYSA-N
#> 12 52-68-6     1.282980 NFACJZMKEDPNKN-UHFFFAOYSA-N
#> 15 55-38-9    12.168138 PNVJTZOFSHSLTO-UHFFFAOYSA-N
#> 18 56-23-5 35000.000000 VZGDMQKNWNREIO-UHFFFAOYSA-N
#> 21 56-38-2     1.539119 LCCNCVORNKJIRZ-UHFFFAOYSA-N
#> 36 57-74-9    98.400000 BIWJNBZANLAXMG-UHFFFAOYSA-N
any(is.na(lc50_sub$inchikey))
#> [1] FALSE

Great, now we can retrieve PubChem CIDs. All get_*() functions return a data frame containing the query and the retrieved identifier. We can merge this with our dataset with dplyr::full_join()

x <- get_cid(lc50_sub$inchikey, from = "inchikey", match = "first", verbose = FALSE)
library(dplyr)
lc50_sub2 <- full_join(lc50_sub, x, by = c("inchikey" = "query"))
head(lc50_sub2)
#>       cas        value                    inchikey  cid
#> 1 50-29-3    12.415277 YVGGHNCTFXOJCH-UHFFFAOYSA-N 3036
#> 2 52-68-6     1.282980 NFACJZMKEDPNKN-UHFFFAOYSA-N 5853
#> 3 55-38-9    12.168138 PNVJTZOFSHSLTO-UHFFFAOYSA-N 3346
#> 4 56-23-5 35000.000000 VZGDMQKNWNREIO-UHFFFAOYSA-N 5943
#> 5 56-38-2     1.539119 LCCNCVORNKJIRZ-UHFFFAOYSA-N  991
#> 6 57-74-9    98.400000 BIWJNBZANLAXMG-UHFFFAOYSA-N 5993

Retrieving Chemical Properties

Functions that query chemical information databases begin with a prefix that matches the database. For example, functions to query PubChem begin with pc_ and functions to query ChemSpider begin with cs_. In this example, we’ll get the names and log octanol/water partitioning coefficients for each compound using PubChem, and the number of aromatic rings within the chemical structure using ChEMBL.

y <- pc_prop(lc50_sub2$cid, properties = c("IUPACName", "XLogP"))
y$CID <- as.character(y$CID)
lc50_sub3 <- full_join(lc50_sub2, y, by = c("cid" = "CID"))
head(lc50_sub3)
#>       cas        value                    inchikey  cid
#> 1 50-29-3    12.415277 YVGGHNCTFXOJCH-UHFFFAOYSA-N 3036
#> 2 52-68-6     1.282980 NFACJZMKEDPNKN-UHFFFAOYSA-N 5853
#> 3 55-38-9    12.168138 PNVJTZOFSHSLTO-UHFFFAOYSA-N 3346
#> 4 56-23-5 35000.000000 VZGDMQKNWNREIO-UHFFFAOYSA-N 5943
#> 5 56-38-2     1.539119 LCCNCVORNKJIRZ-UHFFFAOYSA-N  991
#> 6 57-74-9    98.400000 BIWJNBZANLAXMG-UHFFFAOYSA-N 5993
#>                                                                      IUPACName
#> 1                  1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene
#> 2                                 2,2,2-trichloro-1-dimethoxyphosphorylethanol
#> 3 dimethoxy-(3-methyl-4-methylsulfanylphenoxy)-sulfanylidene-lambda5-phosphane
#> 4                                                           tetrachloromethane
#> 5                    diethoxy-(4-nitrophenoxy)-sulfanylidene-lambda5-phosphane
#> 6                    1,3,4,7,8,9,10,10-octachlorotricyclo[5.2.1.02,6]dec-8-ene
#>   XLogP
#> 1   6.9
#> 2   0.5
#> 3   4.1
#> 4   2.8
#> 5   3.8
#> 6   4.9

The IUPAC names are long and unwieldy, and one could use pc_synonyms() to choose better names. Several other functions return synonyms as well, even though they are not explicitly translator type functions. We’ll see an example of that next.

Many of the chemical databases webchem can query contain vast amounts of information in a variety of structures. Therefore, some webchem functions return nested lists rather than data frames. chembl_query() is one such function.

To look up entries in ChEMBL we need ChEMBL ID-s. These can be found on the PubChem page of each compound within the ChEMBL ID section and can be programmatically retrieved using pc_sect().

lc50_sub3$chembl_id <- pc_sect(x$cid, "ChEMBL ID")$Result
out <- chembl_query(lc50_sub3$chembl_id, verbose = FALSE)

out is a nested list which you can inspect with View(). It has an element for each query, and within each query, many elements corresponding to different properties in the database. To extract a single property from all queries, we need to use a mapping function such as sapply().

lc50_sub3$aromatic_rings <- sapply(out, function(y) {
  # return NA if entry cannot be found in ChEMBL
  if (length(y) == 1 && is.na(y)) return(NA)
  # return the number of aromatic rings
  y$molecule_properties$aromatic_rings
})
lc50_sub3$common_name <- sapply(out, function(y) {
  # return NA if entry cannot be found in ChEMBL
  if (length(y) == 1 && is.na(y)) return(NA)
  # return preferred name
  ifelse(!is.null(y$pref_name), y$pref_name, NA)
})

#tidy up columns
lc50_done <- dplyr::select(lc50_sub3, common_name, cas, inchikey, XLogP, aromatic_rings)
head(lc50_done)
#>            common_name     cas                    inchikey XLogP aromatic_rings
#> 1     CHLOROPHENOTHANE 50-29-3 YVGGHNCTFXOJCH-UHFFFAOYSA-N   6.9              2
#> 2          TRICHLORFON 52-68-6 NFACJZMKEDPNKN-UHFFFAOYSA-N   0.5              0
#> 3             FENTHION 55-38-9 PNVJTZOFSHSLTO-UHFFFAOYSA-N   4.1              1
#> 4 CARBON TETRACHLORIDE 56-23-5 VZGDMQKNWNREIO-UHFFFAOYSA-N   2.8              0
#> 5            PARATHION 56-38-2 LCCNCVORNKJIRZ-UHFFFAOYSA-N   3.8              1
#> 6            CHLORDANE 57-74-9 BIWJNBZANLAXMG-UHFFFAOYSA-N   4.9              0