Allow fragments of aromatic rings to match in RascalMCES (rdkit#8088)

* Allow fragments of aromatic rings to match.

* Use existing code for checking bond is in ring.

---------

Co-authored-by: David Cosgrove <[email protected]>

Code/GraphMol/RascalMCES/RascalMCES.cpp

@@ -350,8 +350,17 @@ bool checkAromaticRings(const ROMol &mol1,
   if (!mol1Bond->getIsAromatic() || !mol2Bond->getIsAromatic()) {
     return true;
   }
+
+  // If neither bond was in a ring, but they were marked aromatic, then
+  // the two mols are fragments so it's ok to match these bonds.
   const auto &mol1BondRings = mol1.getRingInfo()->bondRings();
   const auto &mol2BondRings = mol2.getRingInfo()->bondRings();
+  bool mol1BondInRing = mol1.getRingInfo()->numBondRings(mol1BondIdx);
+  bool mol2BondInRing = mol2.getRingInfo()->numBondRings(mol2BondIdx);
+  if (!mol1BondInRing && !mol2BondInRing) {
+    return true;
+  }
+
   for (size_t i = 0u; i < mol1BondRings.size(); ++i) {
     if (std::find(mol1BondRings[i].begin(), mol1BondRings[i].end(),
                   mol1BondIdx) == mol1BondRings[i].end()) {
@@ -419,15 +428,17 @@ bool checkRingMatchesRing(const ROMol &mol1, int mol1BondIdx, const ROMol &mol2,
   return true;
 }
 
-// Make the set of pairs of vertices, where they're a pair if the labels match.
+// Make the set of pairs of vertices, where they're a pair if the labels
+// match.
 void buildPairs(const ROMol &mol1, const std::vector<unsigned int> &vtxLabels1,
                 const ROMol &mol2, const std::vector<unsigned int> &vtxLabels2,
                 const RascalOptions &opts,
                 std::vector<std::pair<int, int>> &vtxPairs) {
   std::vector<std::string> mol1RingSmiles, mol2RingSmiles;
   std::vector<std::unique_ptr<ROMol>> mol1Rings, mol2Rings;
   // For these purposes, it is correct that n1cccc1 and [nH]1cccc1 match - the
-  // former would be from an N-substituted pyrrole, the latter from a plain one.
+  // former would be from an N-substituted pyrrole, the latter from a plain
+  // one.
   static const std::regex reg(R"(\[([np])H\])");
   if (opts.completeAromaticRings) {
     extractRings(mol1, mol1Rings, mol1RingSmiles);
@@ -660,7 +671,8 @@ RWMol *makeCliqueFrags(const ROMol &mol,
   return molFrags;
 }
 
-// Calculate the shortest bond distance between the 2 fragments in the molecule.
+// Calculate the shortest bond distance between the 2 fragments in the
+// molecule.
 int minFragSeparation(const ROMol &mol, const ROMol &molFrags,
                       std::vector<int> &fragMapping, int frag1, int frag2) {
   auto extractFragAtoms = [&](int fragNum, std::vector<int> &fragAtoms) {
@@ -758,7 +770,8 @@ void updateMaxClique(const std::vector<unsigned int> &clique, bool deltaYPoss,
   }
 }
 
-// If the current time is beyond the timeout limit, throws a TimedOutException.
+// If the current time is beyond the timeout limit, throws a
+// TimedOutException.
 void checkTimeout(
     const std::chrono::time_point<std::chrono::high_resolution_clock>
         &startTime,
@@ -924,8 +937,8 @@ void explorePartitions(
 bool deltaYExchangePossible(const ROMol &mol1, const ROMol &mol2) {
   // A Delta-y exchange is an incorrect match when a cyclopropyl ring (the
   // delta) is matched to a C(C)(C) group (the y) because they both have
-  // isomorphic line graphs.  This checks to see if that's something we need to
-  // worry about for these molecules.
+  // isomorphic line graphs.  This checks to see if that's something we need
+  // to worry about for these molecules.
   const static std::unique_ptr<ROMol> delta(SmartsToMol("C1CC1"));
   const static std::unique_ptr<ROMol> y(SmartsToMol("C(C)C"));
   return (hasSubstructMatch(mol1, *delta) && hasSubstructMatch(mol2, *y)) ||
@@ -1126,8 +1139,8 @@ std::vector<RascalResult> findMCES(RascalStartPoint &starter,
   return results;
 }
 
-// calculate the RASCAL MCES between the 2 molecules, provided it is within the
-// similarity threshold given.
+// calculate the RASCAL MCES between the 2 molecules, provided it is within
+// the similarity threshold given.
 std::vector<RascalResult> rascalMCES(const ROMol &mol1, const ROMol &mol2,
                                      const RascalOptions &opts) {
   auto starter = makeInitialPartitionSet(&mol1, &mol2, opts);

Code/GraphMol/RascalMCES/mces_catch.cpp

@@ -1412,3 +1412,19 @@ TEST_CASE("Atom aromaticity match") {
     check_smarts_ok(*m1, *m2, res.front());
   }
 }
+
+TEST_CASE("Aromatic fragment match") {
+  v2::SmilesParse::SmilesParserParams params;
+  params.sanitize = false;
+
+  auto m1 = v2::SmilesParse::MolFromSmiles("[1*]c([3*])nc[2*]", params);
+  REQUIRE(m1);
+  auto m2 = v2::SmilesParse::MolFromSmiles("[1*]c([3*])nc[2*]", params);
+  REQUIRE(m2);
+
+  RascalOptions opts;
+  auto res = rascalMCES(*m1, *m2, opts);
+  REQUIRE(res.size() == 1);
+  CHECK(res.front().getAtomMatches().size() == 6);
+  CHECK(res.front().getBondMatches().size() == 5);
+}